Over a Barrel (BGM187)
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Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sat Mar 21, 2020 10:06 pm quote
I'm off out shortly to see if yesterday's tweaks have sorted my gear issue.
Before I do, I thought you chaps should probably see this, and be wary of strangers approaching you – no one is safe now.

https://youtu.be/o8slcU6i2gw
Molto Verboso
1980 P125X, 1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 1979
Location: Staten Island, NY
Sun Mar 22, 2020 1:40 am quote
Lol. That's normal in nyc without these circumstances. Love the Avatar update!
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sun Mar 22, 2020 2:35 am quote
We have lift off!
(No sexual favours were exchanged during this zero-social-contact outing).

I don't think I've been off the clock up the back lane before, so that's encouraging; when she's going, she's really quick and lively; keeping her going is a little tricky - just teething troubles I hope.
I'm not too disappointed not to have had a longer run, I was only going to strobe and measure compression anyway today, (had planned my session to be productive whether she rode or not), I started early to avoid people, and didn't want to make too much noise too early on a Sunday morning. I'll venture further afield when I'm warm starting reliably; just don't need the extra aggro.
Spending an hour on clutch and gears on Saturday sorted that problem; just a final small tweak of clutch still needed to stop it dragging/stalling, so that's done and forgotten as an issue.
I still have that odd kick-back, popping or back fire when kicking over; I thought it was a one off last week starting for the first time, but is now noticeable and persistent.
Still lots of kicks to start, then with throttle open, and warm starting is not happening, she bump started OK though. Seems either flooded or rich; had a look at the plug after a fruitless long warm kick-starting work-out – looks wet and rich (pic at bottom of post).
I'd made too much noise for too long by this time, so canned the strobe because it wasn't quite idling anyway and needed bump starting, and I forgot about the compression until I was back indoors – doh!

I guess for now I'll still have to panic buy my toilet rolls on foot, but not bovvered.

Some sounds, vids and pictures below as I sort them:
Videos direct linked here aren't working at present in Edge or Chrome - there's a message on Youtube that things aren't quite normal, and they're only processing in SD - the URL links are still working though.

The Maiden Voyage:
I've left the multi-kick starting in the video because I'm more aware of this kick-back pop. The stall when turning at the end is just a clutch tweak, but restarting is difficult, more of which can be seen in second clip.

https://youtu.be/gFk9Lj8K_Tk

Maiden voyage SOUND:
https://youtu.be/Ru6UJ78evLM

Fruitless kicking:
...Sometimes with a kick-back and that pop again; paused for a breather, to look at plug, and to let flooding clear (pic of plug at bottom)

https://youtu.be/_oeEjsEOC0M

Bump and twice up the lane – bit of revving on stand – stall and pop:
Particularly notice the popping when it stalls pulling away after the revving on stand.

https://youtu.be/D8kT3Qs1kCs

Twice up the lane SOUND– with stand rev and stall with pop:
https://youtu.be/3EigMcOxK_U

Twice up the lane SOUND– acceleration USED FOR DYNO:
https://youtu.be/AKaw30EvjV8


Probable next jobs; another tiny clutch tweak, leaner Pilot, and maybe loose the carb spacer for now. Priority is to just get her starting, running, idling, then strobe. I won't be tearing around for fun for the foreseeable, but it would be good to have her usable for local runs.

Bear in mind, for the sound recordings, this is still completely 1st best guess jetting; no tweaks yet:
45-140, AC120-BE3-MJ140

Plug when don't want to warm start; rich and wet:

No Warm Start Wet Plug.jpg



Last edited by sime66 on Mon Mar 23, 2020 2:19 am; edited 4 times in total
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1972
Location: London UK
Sun Mar 22, 2020 3:01 am quote
Sounds nice. When running. Float spacer is too thick and expect mixture screw is too far out. Mostly float spacer though. Shouldn't flood that bad.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sun Mar 22, 2020 4:23 am quote
I'm going to lose the float bowl spacer for now; just get it starting easier, running and the timing checked.
I'd turned the mix in ¼ turn to lean it a bit, and idle in ½ turn to get it idling for strobing, so if it's still giving starting problems I guess I'll go to 42/140.

You're not bothered about the popping sound?

I know this is wildly premature; jetting in particular is all over the place, and the bumpy lane doesn't give me a decent run, but curiosity got better of me, so I clipped my best 3rd gear .wav and put it into GSF Dyno.
I did it twice, with and without the extra run after I'd missed 4th gear, and both times I'm getting about 19PS/HP, so when jetting is sorted, and on my normal test (slip) road, with a full rev-range 3rd gear run, I reckon I'll break through 20PS/HP.

These are only quick, rough graphs, but still encouraging:
18.9PS @ 6790rpm, 19.72Nm @ 6672rpm, 8837rpm max.
Bear in mind I'm not revving out in 3rd; just riding as quick as the bumpy lane allows.

Jack, you've sometimes referred to your own power estimation calcs; is this something we could do too? Is it something you could share while we might be stuck indoors, or maybe you could just say if you feel that about 20PS/HP sounds likely.

GSF Cleaned Wav.jpg
Cleaned Wav from best 3rd gear recording in previous post

GSF Results.jpg
Looks like there's a 20PS/HP barrier to break through....

Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1208
Location: california
Sun Mar 22, 2020 7:21 am quote
Nice!
Suspect the spacer as well - gas dumping in randomly as you kick - however - suppose you could be getting some kytronic weirdness?
Was this same ignition as on the DR - and was it recently run before coming off if yes?

(going from memory that you are using a kytronic. going for second cup of coffee now).
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sun Mar 22, 2020 8:15 am quote
Same CDI and Kytronik as final DR test runs; no reason at all to suspect them.
Newly rewired and tested stator (by me, and I do mainly trust me to do a decent job).
Timing unchecked still, currently 3mm past 'A' for 26°; it won't be significantly far out, though I wondered whether the popping might be timing slip due to woodruff key damage. I'll check all that when I strobe and adjust timing - all marked up ready for strobing.
I'm still focusing my trouble-shooting attention on carb tweaks and jetting really.
She ain't running bad for maiden voyage!
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1972
Location: London UK
Sun Mar 22, 2020 8:04 pm quote
Wouldn't rule anything out, could be electrics but I doubt it. Being really overrich can damage the plug. Might need a new one already.

There is no reason starting should be bad because of the jetting. For starting only mix screw and pilot are working. If the choke is not shutting off fully this issue happens. Most likely though is the spacer. Reduce to less gaskets and get it starting better. Timing checked and get WOT checked.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7559
Location: Victoria, Australia
Sun Mar 22, 2020 10:43 pm quote
Sime I assume you got the sound recordings from a different device than the one that did the video? On the video all I can hear is wind noise.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sun Mar 22, 2020 11:46 pm quote
Recording:
Ginch: I've gone back and edited my post to make it clearer which ones are ^^ SOUND ^^ recordings; they are below the videos, and generally clipped a bit to concentrate on the relevant parts.

swa et al: (I can't afford a GoPro). I use a cheap and cheerful Chinese headcam, which I try to point at my speedo, GPS (when fitted), gauges and handlebars (rather than the lovely Cornish scenery). On a good day, if I've pointed it correctly, I can see all I need to see, and read the revs and temp. The sound on this is shite; it's in the wind, and just picks up me heavy breathing or swearing at motorists.
For sound recordings (wavs for GSF Dyno) I use a simple voice recorder app on my 'phone, in my pocket. The downside is that the sound I use and the video aren't in sync, so I have to watch the video and make notes which bits of sound I want to clip for dyno.
In addition to that minor extra step in the process, I also haven't worked out if/how you can post a .wav to play on here, so I use Youtube, and overlay an image describing what it is and save it as .mp4, which I can load up on youtube; that's what Ginch was asking about above.

Edit:
swa, you've moved your post whilst I was writing; I'm leaving mine here, but will go and see if you've started a thread; we will need one soon enough.

For anyone reading, the new discussion is here:
http://modernvespa.com/forum/post2392299#2392299
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7559
Location: Victoria, Australia
Mon Mar 23, 2020 2:10 am quote
Sorry Sime, I did see which were which but was initially amazed at the audio you were able to extract from that video! Then realised of course that you must have had a separate recorder.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Mon Mar 23, 2020 2:28 am quote
Ginch, I've just nipped back and highlighted ^^ USED FOR DYNO ^^ to make it clear. Though previous caveats aplly; I'm not jetted properly yet, just got her going, and this isn't a full rev-range (circa 2500-9000) run anyway, so the Dyno exercise was just because doing that was time better spent than watching the porn channel when I was sad and isolated yesterday.

I see also that the direct videos still aren't working, but each one has the URL under it, which does work.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1972
Location: London UK
Mon Mar 23, 2020 2:57 am quote
I see no reason this won't be about 20bhp. For sure it will end up more powerful than the DR. Timings and set up will be better this time around.

If its beaten the max up the lane speed with the spluttering and popping, its going to get exciting quite soon.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Tue Mar 24, 2020 1:53 am quote
Lockdown.....
Yes it's already matched pre-detune DR for revs & speed and exceeded the power, as you say, whilst still spluttering and popping, and just up the lane not on a good road.

20bhp will do me really; otherwise it'll be getting into the realms of needing to upgrade stuff, or it breaking itself every few months.

I'd done a little list for an hour of mid-week car park BGM jobs prior to doing more runs on the weekend, but Bojo says I can't play with me scoot outside now, so progress is pretty much stalled on it for now.

I might have to dig Old Faithful out from under the bed; I could quickly do a measure-up and use the skimmed DR head I have, and make a base packer, fiddle with the Exhaust, open the Transfers and do the Inlet timing. Do it pretty much for zero cost whilst stuck indoors for the foreseeable......

It's either that, or get my kicks from following those who can carry on in their own private spaces; I'm glad there's so much interesting stuff going on here – well done chaps, keep it up.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1972
Location: London UK
Tue Mar 24, 2020 4:30 am quote
Surely you can use your old scooter for getting the shopping as was intended. If it breaks down at the supermarket you have to work on it to get home.
Few trips doing shopping runs and it will be jetted in in no time. Lets hope it's faster than the virus.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Thu Mar 26, 2020 4:58 am quote
Jack221 wrote:
Surely you can use your old scooter for getting the shopping as was intended. If it breaks down at the supermarket you have to work on it to get home.
Few trips doing shopping runs and it will be jetted in in no time. Lets hope it's faster than the virus.
Yes, it's Ok to ride, needs a couple of jobs, and I'll do some 'stealth-tweaking' when the opportunity arises, just isn't that important right now.

To business:

Stuck inside, and decided to do some non-destructive tests and measures; I know it's not as exciting as your Hollywood breaking stuff for science, but take it or leave it; it's going in my build thread for reference to the current on-the-road ponderings.

There will be words and pictures, and I'm not going to skimp on them because scrutiny is good and critical comments are welcome.

We know that Hibbert's scoot doesn't like a 3mm spacer, Jack's likes a 2mm spacer, and I'm undecided, but highly suspicious of my 2mm spacer.

I think we agree that a spacer needs two gaskets, and that they add a minimum of another 1mm.

The first problem was to establish at what level, relative to the outlet pipe in the venturi, the needle valve shuts off; you can't see it inside the carb.

This morning, I rigged up a carb lid with fuel supply in a glass, so that I could mark the level *relative to underside of float lid* the fuel shuts off. I used petrol, not water this time. The float is a Dellorto 4567 "Gr3.7", which weighs 3g on my scales; the needle is a Dellorto 4559 3.6mm, which weighs 1g - scales don't do fractions of 1g. I know my scooter is rarely under these flat, level, still conditions, but it's a number we needed to proceed, and the need to be aware of variables becomes plenty-apparent as I get to the punch line......

That dimension is 17.5mm from fuel level to underside of float bowl lid – I wouldn't bet my life on it, but I repeated experiment three times, and I'm as happy with the number as I'm going to be for this session – though I'll be very happy to hear if others can confirm or dispute it.

I then needed to know where the fuel outlet pipe in the venturi was relative to this level, so measured the venturi height, the dimension from bottom and top to pipe, thus establishing its centreline, then tried to measure its OD, wall thickness and ID to confirm, and establish a dimension to bottom of pipe. I get OD5.2mm, ID3mm, (they do sell them, so someone might have one to measure more acurately, but anyway, there's enough other variables for that to be useful as my best measure.

I also measured the top of the venturi to be 11mm higher than the top of the float bowl.

With a few sketches and calcs I came to the dimensions from top of venturi to be 22.8 to cl, and 24.3mm to bottom of fuel pipe. Bear in mind that I'm sure not all will be identical to even within 10ths of a mm, so nothing is gospel for any other carb (including the one on my scooter; this is a spare Si26 I'm measuring - possibly from a different mould in a different factory in a different country).

So then, taking a carb with just a 0.5mm gasket as an example:
Closed valve fuel level to top of float bowl = 17.5 – 0.5 = 17mm
Closed valve fuel level to top of venturi = 17 + 11 = 28mm
Fuel level to bottom of tube = 28-24.3 = 3.7mm.

As that example already uses one gasket, the following can be estimated for the following float bowl spacer sizes (which raise the fuel level and reduce the 3.7mm dimension):

1.5mm = 3.7 – 1.5 – 0.5 = 1.7mm bottom of fuel pipe to fuel level.
2mm = 3.7 – 2.0 – 0.5 = 1.2mm bottom of fuel pipe to fuel level.
3mm = 3.7 – 3.0 – 0.5 = 0.2mm bottom of fuel pipe to fuel level.


Photos of test, sketches, measures and calcs; I may do a pretty Cad picture or two, if I'm feeling sad and isolated again, but, even with the shabby worktop-quality of the test, it's pretty clear to see how tight the tweaks of the spacer need to be, especially when this info is transferred to a bumpy road, sloshing fuel, a vibrating engine, - and fairly obviously when you think about it, even the fact that kicking it over probably disturbs and tilts it enough to give an embarrassing tell-tale dribble.

-

Fuel Level test - 1 of 3.jpg
Makeshift fuel level, at valve shut-off, test.

Fuel Level test Conclusion.jpg
Conclusion: Fuel shuts off 17.5mm from u/s float bowl lid.

Measuring Fuel Tube.jpg
'Non-Destructive' measuring of fuel tube.

Carb Dims using fuel level from test.jpg
Dims and first calcs - might Cad it up, but serves the purpose as is.



Last edited by sime66 on Thu Mar 26, 2020 9:56 am; edited 2 times in total
Addicted
Honda elite
Joined: 19 Jun 2007
Posts: 972
Location: California
Thu Mar 26, 2020 6:41 am quote
Thank you Sime66!
Molto Verboso
1980 P125X, 1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 1979
Location: Staten Island, NY
Thu Mar 26, 2020 6:46 am quote
uhh.. this is amazing. ha! You are like that tech ingredients guy on youtube! Now the question is at what level is best for the flow without causing flooding? After your little mockup, im pretty surprised that adding a spacer to float really doesn't add much extra fuel, so its crazy how little extra fuel in the float helps with the flow or hurts the flooding. Delicate balance to get it right. I think your results here with some future testing I suspect you will share with us will determine the spacer thicknesses printed up in the future order!
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Thu Mar 26, 2020 7:51 am quote
I don't think it really gives us any answers; just confirms and, for me anyway, gives a better picture, with some numbers, of quite what a fine balance it is between optimum fuel level and flooding problems.
I am also convinced that there will not be one answer for everyone (too many variables); no single cure-all spacer thickness, which is why a set (not including a 3mm) will be needed – say 1.0, 1.5 & 2.0mm. (Or just experiment with stacked-gaskets to get your ideal thickness, and then 3D-print/laser-cut/make/order one).
For me, to absolutely confirm this as my current problem, I am going to start with no spacer, just a gasket, to make sure the problem goes away, and only then to reintroduce a 1.5mm spacer, and tweak from there if necessary.
I'm also going to change my Pilot to 42/140; I can do a lot more with it when I can start it, take it somewhere quiet and have a fiddle, tweak my mix and idle, and check my timing, without this dozen-kicks bollocks to get rolling – that's not OK and must be sorted, first job.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7559
Location: Victoria, Australia
Thu Mar 26, 2020 6:20 pm quote
Wow Sime, you do really have a lot of time on your hands!

What I would be very very interested to see your take on is this test - normal vs Cosa type lid/needle. I don't think this test was fully explored... let me know what you think.

https://youtu.be/opZXBGud3vw

Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1972
Location: London UK
Thu Mar 26, 2020 9:31 pm quote
Some fine experimentation there. So on a standard PX SI carb 3mm is out. 2mm might work (as mine does) but 1.5mm really should be ok for everybody.

Interesting to see that the float level really isn't that high. Guess about 20mm from the level to the main jet hole. Every mm counts. Add 1.5mm and 7.5% richer. Sure the science isn't quite so simple but seems to work that way.

Once your right into the shopping runs you can decide how much you need.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Fri Mar 27, 2020 12:58 am quote
Wow that 2T mix really gives a thumping hangover; I only had the three small glasses.

Ginch, the best way to consolidate test results is for someone to repeat the test and get the same result, so I'm sure FMP wouldn't mind, but I don't have the larger-valve float bowl to test. I've also never had fuel starvation problems, so have never given fuel flow rate into float bowl much detailed thought. What I have always done is the carb float bowl lid mods, to make sure fuel gets from banjo, through slot into filter chamber, through filter, and down to needle valve, and I think without those mods a larger needle might well give no better flow; maybe that's the reason for FMP's conclusion. I see his point that fuel will take the easy path past the needle and the holes are wasted, but if that's so just open the holes too. If, as he seems to suggest, a larger needle makes no difference because there isn't enough flow to use all the holes, then the restriction must be further up the line, hence my comment about float lid mods. Flow rate into bowl is another subject really, and needs different taps and lids I don't have.

Jack, you got me thinking over coffee this morning, so I had another quick measure to follow up your train of thought.
See scribbled sketch below, but I agree with a 1.5mm spacer, which is a 2mm increase with the second gasket – see sketch for clarification, there is (roughly) a 9.1% increase in fuel depth, and a 11.8% increase in depth above hole into MJ well. If you have five minutes, I, and others who have asked this and I've tried to fumble through an answer, would like to know how this can be stated as “X% richer”; my guess, some pages back, is because of the greater head contributing to the vacuum pressure in the venturi, but is there even a bit of basic science you can share to enlighten your followers?

Of course, if it's just more fuel height above the hole we need, we can achieve that without raising the fuel level, by lowering the hole!! Where's me JB weld and drill..................

fuel depth percentage increase with spacer.jpg

Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Fri Mar 27, 2020 2:05 am quote
...and another thing; when I was writing up my quick blurb about cameras the other day, I nipped onto Ebay for some links in case anyone asked, and I stumbled on a listing for one of those older (better quality) one's, new in box, for £6 + p&p (bloke having a clear out). Thinking that at worst, if it was duff, I could transplant the battery and 'O' rings into my old one I grabbed it, and it arrived today. The new spec says it's 1080p, and it works on my PC, has updated the date like it's supposed to, and I've done a quick recording round my flat. So it looks like I've upgraded my future recordings for a tenner! (or three bog rolls in the new currency). I've also stuck a sliver of foam over the mic, which I recall helped with the old one; it'll cut wind noise, but will it still record the engine enough to use it in GSF Dyno? We'll have to wait for Bojo** to let me out to play...............

(Stop Press: Bojo** has tested positive for coronavirus, so now over to Cummings without further pretence of who's calling the shots in No.10).

1080p.jpg

Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1208
Location: california
Fri Mar 27, 2020 6:42 am quote
Quote:
I've upgraded my future recordings for a tenner! (or three bog rolls in the new currency).
I'm not sure about all the math(s) but there is ample evidence that this virus is having a positive effect on your sense of humor.
🙂

Last sketch was also down right understandable.
Was also curious about the "x% richer" that Jack posted.
Assuming your system can feed the chamber at the same or better rate than it drains - you would maintain this slightly improved head pressure.
Jack was doing head pressure calc (20mm +1.5mm is 7.5% higher).
Does this translate directly to richer?

Unrelated - related - not sure: When I re-assembled yesterday with the chamber well hole enlarged - scoot seemed to run very differently - as if it had gotten much leaner or much richer on lower end of revs/throttle. Wouldn't have thought that should effect low end based on understanding of the science here regarding head pressure.
Which then of course raises the question - am I understanding the science here...
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Fri Mar 27, 2020 8:05 am quote
Let me make the maths simple for you.
Say I've got myself a stockpile of 20 bog rolls, and during the week I use half a bog roll, but buy two more:
20 - 0.5 + 2.0 = 21.5br; that's 7.5% richer!
Addicted
2007 Stella 150
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Fri Mar 27, 2020 3:09 pm quote
sime66 wrote:
Let me make the maths simple for you.
Say I've got myself a stockpile of 20 bog rolls, and during the week I use half a bog roll, but buy two more:
20 - 0.5 + 2.0 = 21.5br; that's 7.5% richer!
What's a bog roll?
Enthusiast
Joined: 22 Jul 2018
Posts: 73

Fri Mar 27, 2020 3:51 pm quote
Pretty sure it means toilet paper.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1972
Location: London UK
Fri Mar 27, 2020 6:55 pm quote
Nice comparison. Calculating exactly how much about as pointless as panic buying. Too many formulas involved and who knows how it works anyway.

The extra head pressure would be fairly linear but the flow through the jet hole and main jet is a curve. The higher level at the atomiser will emulsify more fuel and being closer to the exit more will mixture will be drawn in for less vacuum; also another delivery curve.

We know it works. Higher float level on any carb on any engine makes it richer. How much exactly, we can judge by the size of the jets. With our situation need to be rich enough to keep the main jet down. Less than 140 and target near 130.

Now Bojo is not watching, time to go for a ride.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Fri Mar 27, 2020 10:19 pm quote
OK, so we're not going to put numbers into it and predict results; too many variables and unknowns, but I had a thought overnight, before I'd seen your reply saying that trying calculate it is pointless, and which I'm going to record anyway, though it does seem the subject has exhausted itself for now.
We have %ge change in fuel height (approximately linear with head); if/when we have some spaced and jetted carbs, it might be interesting to know by what %ge we dropped the MJ. We also need the drill hole orifice too, although I think mostly we're on Ø2.1mm, but I will increase mine if I need to reduce my MJ more.

If later we can say, just as an example: “Increasing the fuel height 10% enabled me to drop from MJ140 to MJ132, which is 11% smaller in area.” It might be interesting to have a few of those different results recorded.

(Or maybe, I have just had too much time on my hands this last week).

MJ well drill hole:
Ø1.8mm = 2.54mm²
Ø2.1mm = 3.46mm² = +36.1% area
Ø2.5mm = 4.91mm² = +92.9% area (and 41.9% area increase on Ø2.1mm)

Main Jet:
130 (Ø1.3mm) = 1.33mm²
132 (Ø1.32mm) = 1.37mm² = +3.1% area
135 (Ø1.35mm) = 1.43mm² = +7.8% area
138 (Ø1.38mm) = 1.50mm² = +9.3% area
140 (Ø1.40mm) = 1.54mm² = +16.0% area

140 (Ø1.40mm) = 1.54mm²
138 (Ø1.38mm) = 1.50mm² = -2.8% area
135 (Ø1.35mm) = 1.43mm² = -7.0% area
132 (Ø1.32mm) = 1.37mm² = -11.1% area
130 (Ø1.30mm) = 1.33mm² = -13.8% area

We know it works, we know the extra head pressure will make it richer, which will enable the MJ to be smaller, which we need it to be because this carb is easier and more likely to be jetted correctly if the MJ is nearer 130 than 140.

7.5% increase in fuel depth is richer, but unlikely to be precisely 7.5% richer.

Maybe later we can record some results to see if we can make more sense of it. For now; just two jobs arising from it (which we all already knew before all this malarkey above):

1) Get a float bowl spacer that doesn't cause flooding and starting problems.
2) With that spacer (after the pre-amble setting up of timing, Pilot, mix etc) ensure there is a WOT splutter – hopefully somewhere near MJ140, then drop MJ a couple of sizes, before going back to Pilot.
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Sat Mar 28, 2020 5:45 am quote
sime66 wrote:
OK, so we're not going to put numbers into it and predict results; too many variables and unknowns, but I had a thought overnight, before I'd seen your reply saying that trying calculate it is pointless, and which I'm going to record anyway, though it does seem the subject has exhausted itself for now.
We have %ge change in fuel height (approximately linear with head); if/when we have some spaced and jetted carbs, it might be interesting to know by what %ge we dropped the MJ. We also need the drill hole orifice too, although I think mostly we're on Ø2.1mm, but I will increase mine if I need to reduce my MJ more.

If later we can say, just as an example: “Increasing the fuel height 10% enabled me to drop from MJ140 to MJ132, which is 11% smaller in area.” It might be interesting to have a few of those different results recorded.

(Or maybe, I have just had too much time on my hands this last week).

MJ well drill hole:
Ø1.8mm = 2.54mm²
Ø2.1mm = 3.46mm² = +36.1% area
Ø2.5mm = 4.91mm² = +92.9% area (and 41.9% area increase on Ø2.1mm)

Main Jet:
130 (Ø1.3mm) = 1.33mm²
132 (Ø1.32mm) = 1.37mm² = +3.1% area
135 (Ø1.35mm) = 1.43mm² = +7.8% area
138 (Ø1.38mm) = 1.50mm² = +9.3% area
140 (Ø1.40mm) = 1.54mm² = +16.0% area

140 (Ø1.40mm) = 1.54mm²
138 (Ø1.38mm) = 1.50mm² = -2.8% area
135 (Ø1.35mm) = 1.43mm² = -7.0% area
132 (Ø1.32mm) = 1.37mm² = -11.1% area
130 (Ø1.30mm) = 1.33mm² = -13.8% area

We know it works, we know the extra head pressure will make it richer, which will enable the MJ to be smaller, which we need it to be because this carb is easier and more likely to be jetted correctly if the MJ is nearer 130 than 140.

7.5% increase in fuel depth is richer, but unlikely to be precisely 7.5% richer.

Maybe later we can record some results to see if we can make more sense of it. For now; just two jobs arising from it (which we all already knew before all this malarkey above):

1) Get a float bowl spacer that doesn't cause flooding and starting problems.
2) With that spacer (after the pre-amble setting up of timing, Pilot, mix etc) ensure there is a WOT splutter – hopefully somewhere near MJ140, then drop MJ a couple of sizes, before going back to Pilot.
I'm in the middle of jetting my 20.20, waiting on a idle jet a bit smaller than a 55-160, it is a bit rich low-midrange rpm, 1/8 to 1/4 throttle ish, low 11's high 10's on my AFR. Do you think adding more fuel will richen up the mid range?

While still assembled and mounted on the scooter. Do you think it would be worth removing the main jet stack, measuring the fuel depth? You could record that, then drip fuel into the main jet well until fuel comes out of the holes. Measure what that fuel depth is from the top of the main jet well, record that depth. This would allow you to determine how far you are below the point where fuel is just going to drip out.

This would remove variation from setup to setup, some of us maybe at 2mm from overflowing already while some are at 4mm or more. That would explain why different spacers work better for some than others. The question I have is how do we reliably measure fuel depth in the main jet stack well? Kind of hard to see in there and know when you are touching the fuel. Those are my miscellaneous ramblings for the moment.
Molto Verboso
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Sat Mar 28, 2020 8:08 am quote
Sime - tho some may say about my maths - that some perfectly good village is missing their idiot - both Hebbert and I experienced MJ size drop due to hole size.
Let's stay focused here please boys.

On my set up, with 24/24 SI, once broken in, I was able to run WOT at nice temps and max speed somewhere around 135MJ (BE3/AC120).
132MJ starved the motor at WOT (ask me how I know - see note above about village).
SI carb had a 1.8mm hole and no spacer at the time - though it did have larger needle in it that is supposed to allow more volume flow I believe.

I drilled the float chamber hole from 1.8 to 2.3.
My jetting immediately needed to drop - splutter at 138 and well rich at 135.
Carb now wants to be at 130 ~132.

Simple math - increase in hole size drives me down about 1-2 MJ sizes.
Hebbert can comment on what his numbers were for float bowl hole, and MJ sizing were, before and after - though I think he included the spacer addition?
Hooked
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Sat Mar 28, 2020 10:03 am quote
Christopher: If by 'adding more fuel' you mean increasing the bowl fuel level with a spacer, then yes, I think it will richen both jets, so the whole range, because of the raised height (for same vacuum pressure) in both jet wells. Jack's just covered it on CM's sidecar thread.

I don't think I'd find much joy in trying to measure the fuel level in the jet well whilst carb was still on the scooter; I didn't even think it was worthwhile trying that indoors, which is why I took the float bowl lid off and measured it in a glass (the depth the fuel cuts off – see above a few days ago). Having said that, I'm wondering if some sort of graduated float might work, (I've just tried lots of pen inners, the tube off a can of WD40, a cut-off wooden skewer, a coffee stirrer, and a strip of foam – which worked best, but isn't ideal) where you could mark the level, which wouldn't have to be precise, then fill until you get a drip and mark it again; That could be fairly accurate with the right float.

....I just had a quick go, and I think it's too imprecise; I could say I marked a 4mm rise, when by measurement the other day (without a gasket 'cos I've nicked it), I should have got 4.2mm. - But the marks I managed to make on a soggy bit of foam floating in the well are about 1.5mm thick anyway, and the float has to be so light to float that it sticks to the well wall too – far from satisfactory method.

Think I'd take the carb off If I really had to know, but maybe adding gaskets 'till it floods is the simplest way to go.

-
-
sime66 wrote:
Stuck inside, and decided to do some non-destructive tests and measures; I know it's not as exciting as your Hollywood breaking stuff for science, but take it or leave it; it's going in my build thread for reference to the current on-the-road ponderings.
(Bad form to quote myself really, but needed to here I think):

CM: Surely measuring stuff, adding and subtracting, doing a couple of sketches and calculating some areas & percentages isn't big maths if you slow down long enough to follow. I'm methodical, you seem to want the punchline without the process; we're different in how we do things, and I'm not claiming to be right or wrong; just doing what I do, which I have also acknowledged might not be very entertaining to follow.

We all already know an increase in well hole drill will enable a reduction in MJ size; following on from Jack's comment the other day I was exploring whether the fuel level's effect on the MJ size can be quantified at all, but it seems not, certainly not without some labourious exploration of a complex subject.

This recent discussion, which is now pretty much wrapped up anyway except for any results as they come in***, was primarily concerning float bowl fuel level, though this morning I also reiterated that the well hole drill size was relevant too – which has been previously discussed at length on several threads.

The line: “Simple math: increase in hole size drives me down 1-2 MJ sizesis not news, is not strictly on-topic, nor does it really make for any usable result*** – so "lets stay focused here please boys".

I know what I'm doing on mine when I can; I was just trying to make best use of my down time, and sharing my thoughts and findings in case they're relevant to others too, but as I said last Thursday, anyone can take it or leave it, (refer above).

I think I've exhausted this topic until I'm back on the road, but will continue to enjoy following your progress, when I can keep up with it! ......

Last edited by sime66 on Sat Mar 28, 2020 11:22 am; edited 1 time in total
Addicted
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Sat Mar 28, 2020 11:03 am quote
Thank you for all of the efforts, maths, sketches, scientific experiments and debate. Was suspicious the spacer was dumping fuel and think it is in my case almost livable if on flat ground. Looking forward to trying the 2mil spacer if it ever arrives. If there was a 1 or 1.5 I'd get one but like the stainless steel quality. My main jet passage is 2mm.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sat Mar 28, 2020 11:36 am quote
Cheers Hibbert, I see you making progress with your P200 Malossi and PHBH carb too, but those clips and needles tweaks is a subject I've never tackled, so find it difficult to follow the detail with that one. I watched your recordings though, and your last post looks like you're getting there.
Molto Verboso
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Sat Mar 28, 2020 2:07 pm quote
Quote:
CM: Surely measuring stuff, adding and subtracting, doing a couple of sketches and calculating some areas & percentages isn't big maths if you slow down long enough to follow.
Actually - that was my way of complimenting your work in self deprecating fashion.

Hole size - I thought my real life data was complementary to your calcs - given that I had the unique baseline number of exploding my engine - giving us a hard number to start from on MJ.

My point was: I was surprised by the magnitude of change going from 1.8 - 2.3 brought. Remember - my 1.8 was pre-drilled by DRT who have significant experience and rate it up to 208CC.
I considered that there must be diminishing returns on hole size - and that I might already be at or near optimal
Your post made me think about that.
5+ points was more significant to me than expected.
More method to the madness then it may appear sometimes...
Veni, Vidi, Posti
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Sat Mar 28, 2020 5:25 pm quote
sime66 wrote:
The line: “Simple math: increase in hole size drives me down 1-2 MJ sizesis not news, is not strictly on-topic, nor does it really make for any usable result*** – so "lets stay focused here please boys".
Actually for me this was the most important thing of all (thanks CM). I know it's not about spacers but was very clear.
Sime, you appear to know what you're doing - I have to assume this because, not unlike Charlieman, I was sick the day we had maths at school.
You have lots of numbers and anwers to the numbers and my brain just glazes over. To a person who struggles with this type of thing, nothing is simple. So conclusions are the only part I can read with confidence, if it's clear.
+++++++++++++++++++++++++++++++

What Jack said regarding the higher level of fuel meant the atomiser would "emulsify more fuel" doesn't really make sense to me, although I may have taken it out of context... I think the main point here is that the higher level of fuel in the jet well means simply that more fuel and less air leaves the mixer tube. Therefore the higher level creates a richer condition by itself and the main jet becomes a little less important... hence the drop in size of the main jet.
Think that brings the main jet size discussion back on track!

++++++++++++++++++++++++++++++++

I've just seen this old thread on another forum by Vespasco (pretty sure this guy is Bholinath on the old Stella Speed forum for those who were around then), he did a lot of experimentation to arrive at his results. Sime I know you've seen it because you posted a reply in 2015! I've collected a few of his comments throughout the thread to keep it pertinent.
Vespasco wrote:
EDIT:
CAUTION:
after several experiments i found that...

Drilling your carb could make it over rich and very difficult to jet!!!
Do not drill the carb passageways too large or the carb will be very rich in mid, lean at WOT and a pita to dial in.
Although by drilling out the fuel supply holes it did actually improve fuel flow some what BUT ....
I also found the problems ive had recently with trying to dial it all in. It was near impossible as the carb was now soooo rich, especially between 4000-6000rpm i couldn't do much to get it running smooth.
Before, I spent a lot of time swapping jets, atomizers, slides and have learnt that you CAN drill out si carb and it WILL Supply more fuel to the sysytem...BUT.....!
If you drill too large...(from my guesstimations that would be anything bigger than the needle valve hole, which is around 2.3mm) if you drill too large it WILL cause problems!

Ive ran the carb for years, running smoothly but with the main jet feed hole drilled out to only 2mm...this seemed to work ok.
What ive found in the past few days is that drilling it out to 3mm causes very rich mid range.
Jet Eye Master
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Sat Mar 28, 2020 8:28 pm quote
All we are really interested in is the size of the main jet, so it is the most relevant point. Increasing level and drilling over 2.0mm until the final main jet is around 130 is where we need to be.

Ginch, what I was meant was there is more fuel emulsified for the same air. There is no less air. The air from the air corrector is at the same pressure and flows the same as before. If the level in the well has increased it will take more rpm for the level to drop and this draws more fuel out for the same air as before.

Once CM, Hibbert and Sime are set up and running smooth it should be easier to analyse.
Hooked
1984 PX(BGM187)EFL
Joined: 14 Apr 2017
Posts: 361
Location: Cornwall UK
Sun Mar 29, 2020 2:31 am quote
I do think we've all said what there is to say on this subject for now, but it's rude not to reply, so I'll do one more careful post on it; no offence is intended at all, and after that I'll take the feedback about my presentation on board and say no more, but hope others consider my point of view too. I do love this forum, all the different projects and different approaches to them; time spent here reading lots of different threads, (and contributing on the very few of those where I can), is really worthwhile for me.

To my point:

There are two factors, and two discussions going on about how to keep the MJ size down, whilst related they are not the same:
* The drill hole size (that we enlarge between float chamber and MJ well – an old, much discussed subject), and
* The fuel level in the float chamber (that we control by adding spacers where the gasket goes – a relatively new subject, to me anyway).
This last few days stuck indoors I've been talking about the spacers, though couldn't ignore the relevance of the drill size, which has been discussed several times previously, and we know we can increase to reduce the MJ. That distinction is getting muddied here, which means those just reading the punchline are missing the point. At this stage in my thread, as I said yesterday, it's got to where I better understand it for myself, and why the spacer tweak has to be so tight, but I've gone as far with it as I can for now; whether it's been of any use to others is out of my hands.

If the punchline now is just, as said here and repeated elsewhere this morning “All we are really interested in is the size of the main jet”, and that's all anyone wants from it then that's OK with me, but read the second sentence too, maybe.

Ginch, it's interesting you mention Vespasco; I miss him on the forums, we used to bounce a lot of ideas about, and sometimes go into stuff too deep until we got ourselves totally off-topic and confused, and bored everyone else to distraction with it, but we were learning. Some of those who didn't follow, or want to follow, were down right obnoxious and obstructive, and it became a real chore to continue; that doesn't happen here where it's much more positive and constructive. You're right, he is Bholinath on here and elsewhere, and he is also the Scott I referred to on this thread on p6, March 12, when I said to Jack that “I keep in mind the aggro Scott had when he drilled several Si26s too big and scrapped them”. That was when I was hesitant (yes, I accept that I'm hesitant) about drilling my 1.8mm hole larger before I knew I needed to because I believed it to cause other problems. You'll probably also have already found from old posts that we learned the Dyno stuff by bouncing it around together too; lots of other subjects too where we talked a lot of nonsense, swapping ideas before making any progress or conclusions.

All the measures, calcs and tests aren't much real use unless they can be checked by someone else, (a point I made to you a couple of days ago when you mentioned FMP's flow/valve tests), so the working has to be shown; I do genuinely feel that here stuff is being accepted without scrutiny. It's something I'll get used to, but me and Vespasco would always check each other to keep each other straight before going deeper down whatever hole we were exploring. That isn't really happening here, whether that's because it's too hard (which surely is unlikely, since we can all measure well enough to build engines and other complex stuff that needs all sorts of calcs), or just pretty boring compared to messing about in the garage or on the road, I don't know, but I will be conscious in future not to bloat posts with too much data, but bear in mind I'm also making a record of this build for myself for reference later, so if I want something in it I will post it. (I have all my threads from that forum on a CD of .pdfs, taken before Photobucket removed all the photos, sketches, calcs, etc.). All I've just been doing last week is some thinking and testing (and sharing it) until I can do the fun stuff again; it's pretty irritating for someone to dip in, gloss over all the background, take the punchline, tell me I'm making it too complicated, and give the 'stay focused' team talk, whilst missing the point and, by doing so, inadvertently steering it back to an old safer subject. That was the matter I felt needed addressing yesterday, but this morning I'm more of the opinion that looking at the subject has served its purpose (which, I concede, was partly me understanding it better and partly just making use of my idle time) and it can die a natural death now.

I'm itching to make a point about the difference in area and %ge area as you increase a circle (hole size/jet size) in 0.1mm increments, because it explains what you're talking about CM. If you picture that you're adding 0.1mm as a band around the edge, so the larger the hole, the greater difference each 0.1mm change makes (that depends on whether you're considering area or %ge area though) – it isn't a straight line. Should I show a table? A graph? Or keep my thoughts to myself?
This morning I've compared a 1.8mm to 2.1mm drill mod, with a 2.1mm to 2.4mm drill mod; both 0.3mm bigger, but not the same change in area or %ge area – (or perimeter come to think of it, which I didn't until now, and can't be arsed to go back and look at, but might be relevant to friction though), so why would they be expected to have the same effect on MJ? That's that point without the numbers; is that better to read? To me it would be better to show how I got to thinking it was worth making the point and had checked myself before making it, actually share the data, and then have someone check and confirm – or to say, yeah but that's bollocks because it's so small it's not relevant; I'm learning too. Anyone want to check the point and tell me whether or not it's bollocks? Thought not.

So to summarise:

“All we are really interested in is the size of the main jet”.

Have a nice day everyone; glad to say I've got plenty of work to do next week to keep my focus on other stuff, so won't be 'flooding' (ha ha) my build thread more for now, but will be back soon – with numbers (in the form of results, and for my record if nothing else).......

Lets move on now.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
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Sun Mar 29, 2020 1:42 pm quote
Sime - please, please don't think I was trying to discourage you from recording/posting all your calculations - I think it's great, and what you're doing is useful. The point I think I was trying to make is that not everyone understands it - me in particular - so I skip over it. Yes I'll definitely miss stuff, useful stuff, but that's on me. If your intention was to relay your findings to as many people as possible then maybe a summation would help, but if it's just to record and bounce ideas off people who can follow, then just carry on! I'll still follow and see where it leads.
But I still think the rise in richness is mainly due to the height of fuel within the mixer.
Hooked
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Mon Mar 30, 2020 12:10 am quote
The chaos in the mixer tube around the atomiser remains a mystery to me; one that I'm not sure anyone knows for sure. I'm not good at chaos; it unsettles me.

In fact I try hard not to say I have answers - just ideas and clues, so the second scenario fits better, where ideas are being explored, rather than firm conclusions offered. You'll recall that I was very careful, when Hibbert and CM were building, to show or tell them what I had done, rather than tell them what they should do; I don't claim to be right about stuff, just doing my best with what I'm learning. We're fortunate to have a premier league expert helping us all here; I'm Sunday morning old-boys knock-about by comparison.

Anyway, it's all good; everyone is stressed/bored, worried/couldn't give a damn, stocked-up/starving, stir-crazy/loving the great outdoors, and dealing with things as best they can. This just isn't important.

Today's summary:

Keep calm and carry on

Or for those old enough to remember:

You've all done very well

(Going quiet on this one 'til the scoots buzzing again, but following and looking forward to seeing how dyno goes elsewhere - might need some maths).......
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