Stella 2T highway/performance upgrades
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Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Tue Jun 02, 2020 11:50 am quote
Todays tests involved changing the ignition timing from 24 degrees on the T mark to 23 degrees, going down the next leaner main to 135 and going a few sizes down on idle jet from 55/160 (2.91) to 45/140 (3.11). I was able to kill the engine idling by closing the air mix screw completely. After dialing in the air mix screw its settled at 2.5 full turns out now.

Oddly enough, going down to 135 mj on a 1 degree more retarded ignition setup, I thought it would be more peaky and yet it felt alot like the 138 at 24 degrees. The main difference was everything is cleaner throughout, but the spluttering and bogging changed slightly. Overall I think it is very close to dialed in as quick accelerating from stop up the gears it barely splutters, except that now it feels like there is a slight dead bogging spot at full throttle during mid rpms until it gets to very high rpm which it finally clears up. low rpm doesn't have any bogging anymore but holding mid throttle has spluttering that doesn't seem to affect the acceleration or deceleration much. Plug is looking much closer to correct starting to turn brown now, but still looks a little rich.

I might even say that 135 MJ on this 1 degree more retarded timing is now too rich and could possibly go down to 132 MJ (125 measured).

As far as temps, going from 24 to 23 seems to have settled the temps more stable they really are solid around 220-250 at casual city driving with lots of lights. Holding for longer at WOT it will climb to 275-300. It might hold at 300 for long wot runs or it might just slowly climb up a little above 300F, not sure. It feels like it is really close in terms of solid cruising temps. Even with the drastically leaner idle jet from my initial starting jet size the idle settles really fast and temps go down at red lights. Its amazing how this thing can take a much smaller idle jet now despite being more displacement and larger carb than when it was stock.

The finish line feels visible in the distance finally! Now its just a matter of cleaning up the slight spluttering at mid throttle and the little bit of bogging at WOT. I am also wondering if Jack is right and maybe 1 more degree retarded timing will really solidify the stable temps. After reviewing the SIP vape timing diagram again, I realize that 23 on the T mark is actually 24 at 4000 rpm and 17 at 8000 rpm so it might still have a little more room to go down to 22 on the T mark which would be 23 at 4000 rpm and 16 at 8000 rpm. I also have a few smaller idle jets he suggested on order waiting to ship and try those out to see if those would clear up the low end splutter. 45/160 and 48/160 idle jets.

Audio files of two parts of my run. you can hear now if i hold mid to 3/4 throttle at cruising speed for long it does not sound spluttery much anymore and just sounds like a consistent healthy engine.
https://soundcloud.com/sean-simpson-231097141/sets/malossi-177-rebuild

plug photos below all on 45/140 idle. 2.5 full turns air mix. 120/be3/135MJ (128 measured).

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Ossessionato
05 Stella, '62 VBB, 76 Sprint V, 63 GL
Joined: 16 Jun 2011
Posts: 2567
Location: Chicago. Well, Evanston, but that's almost Chicago
Tue Jun 02, 2020 6:47 pm quote
You'll find 70 MPH on a Stella is overrated, especially if you haven't upgraded your suspension and put tubeless rims & tires on it.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Tue Jun 02, 2020 6:50 pm quote
luckily everything is upgraded on this over the past 25 pages! Complete new sip performance shock set and tubeless rims! at this point the only things left stock are the frame components and the wiring harness.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2134
Location: London UK
Tue Jun 02, 2020 9:12 pm quote
Getting closer. Timing needs to go down another degree and main jet down another two sizes.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 10:31 am quote
One degree retarded to 22 on the T which is 23 at 4k and 16 at 8k. Went down cautiously one jet size to 132 (125). Runs fast and strong. Still some slight stuttering with a little bogging at 3/4 throttle. Low end still minimal stuttering that doesn't affect the Accel decel. Compared to yesterday it's improving. Temps even more stable and stay below 250 city consistent.. Wot run it finally feels like it peaks out at the top rpm and bounces up and down at that limit as opposed to not quite getting all the way up there before losing steam yesterday. Plug still looks a little too gray and not enough Brown but I'll go with that as is because it runs well and temps are safe for breaking in city driving.

I think beta testing jetting is over and it gets the safety stamp for city driving on this jetting to call it V001. I'm going to continue with this and more slowly make changes to solve the remaining issues over time by running with one jetting for a week or more and just make some minor tweaks to air mix screw to see if i can dial this idle jet in. I may also try a 130 mj as Jack suggested to see if that solves the 3/4 throttle bogging, but i want to wait to finish breaking in around 500 miles on city driving. Once i get 500 miles on this rebuild I'll start taking it on highway to test wot runs on highway and see what the true top end heat response is and make some finer mj decisions based on that whether it's down to 130 or up to 135 based on temps at those speeds. Idle jet may still be able to go a little leaner but i think this might be the correct one now with some air mix screw fine tuning.

I have currently gotten it up to 60 in third on back roads without even trying and it feels like a rocket. Shifting into 4th at that rpm range and i can tell it wants to go fast but I'm being patient and holding back a true top speed run for at least 500 miles. I'm at about 175 miles on this rebuild now with about 100 of it in close to correct jetting. Fuel economy is greatly improved from all this leaning out and fixing the flooding. Haven't kept track of the fuel economy during this beta testing but starting now i will track that and see where it lands. Hoping it's in the mid 40s. Would be very happy if it was in the mid 50s.

Photos are 45-140 idle. 2.5 turns air mix. 120/be3/132(125). 23-16 timings (22 on the T mark)

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Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 10:44 am quote
Now take this with a pinch of salt, as I say been away from scooters for 3 years.
Your main jet set up is very very rich is there a reason?
I take it you have an electronic variable ignition add on?
On your blogging issue, what slide do you have in the carb?

On my scooter I have blocked the Oval hole on the carb as this is a second air passage that bypasses the Ventura and adds atmosphere under the slide, if you have the type with groove cut.

Ps at work, on a collection, I'm going to have to read this thread backwards on my laptop, too much to do on a phone

Pps
Scooterhelp gearing calc is out I have found. My Sip speedo said I hit 8300 rpm in fourth, Max Speed 73 mph, according to scooterhelp I was hitting plus 80mph with a 22/68 setup, not true
The Stella LML speedo on my mates UK version was way way way over. Plastic back, tape phone to scooter, I used Ulysse pro app, I bought it, still dont really know how to use it!
My max temp pre heat seize 328F, I have my heat coupler within a rubber tube at spark plug ring, I found that if I didnt insulate it from the air flow it gave very low readings
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 11:18 am quote
Darren.H wrote:
Now take this with a pinch of salt, as I say been away from scooters for 3 years.
Your main jet set up is very very rich is there a reason?
I take it you have an electronic variable ignition add on?
On your blogging issue, what slide do you have in the carb?

On my scooter I have blocked the Oval hole on the carb as this is a second air passage that bypasses the Ventura and adds atmosphere under the slide, if you have the type with groove cut.

Ps at work, on a collection, I'm going to have to read this thread backwards on my laptop, too much to do on a phone

Pps
Scooterhelp gearing calc is out I have found. My Sip speedo said I hit 8300 rpm in fourth, Max Speed 73 mph, according to scooterhelp I was hitting plus 80mph with a 22/68 setup, not true
The Stella LML speedo on my mates UK version was way way way over. Plastic back, tape phone to scooter, I used Ulysse pro app, I bought it, still dont really know how to use it!
My max temp pre heat seize 328F, I have my heat coupler within a rubber tube at spark plug ring, I found that if I didnt insulate it from the air flow it gave very low readings
I have done some work to this got a long stroke crank, a lot of opening up of the ports widened the exhaust to 68% with some more profiling to the exhaust port. No air filter so its the equivalent of a venturi. This is why it is much richer. Jack still thinks it is a little rich and I am inclined to think he is right from this run, but at this point it is running well enough that I feel it is a good foundation to very slowly work down over time to get some real world riding experience before making more moves leaner.

slide is cutout underneath with dimples on top. I have also noticed teh scooterhelp estimates are a little off but generally close enough. Currently my real world mph mentions are stella speedo which is known to be approx 5-8mph faster than gps, but that hasn't concerned me yet as I was effectively just getting the carb set up in the correct ballpark. Now that I am close, I will actually start using the phone gps to get confirmed speed numbers.

BTW, the 2nd gear WOT run I just tested at 132 mj with the plug photos previously show this on the GFS dyno. Tried to be very accurate with the weight, temp and air pressure settings to hopefully get it a little more accurate. So I am getting close to the peak RPM jack targeted for the timings this top end is set up for. Power I think will increase slightly with slightly leaner MJ. I will try to get a good range of dyno graphs at these bracketed main jets now to see where is the ideal target in terms of power, within temp ranges.

CHT/EGT I have a westach dual gauge with westach probes built for aeronautics use. It seems to be very accurate, my only problem is I installed it below the ignition key and my tachometer on the handlebar so I've got some obstructions to viewing it currently. Gonna move the tachometer to the other handle to get that out of the way. I've also gotta get my tach connected to ignition pulse as it's not reading anything now that my electronics are DC. And yes I'm on a sip vape variable ignition.

22Tmark_132mj_45-140idle.png

Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2134
Location: London UK
Wed Jun 03, 2020 11:57 am quote
Plug looks too hot. Take the main jet back up one size. Grey is not a good colour and that is an 8 or 9 plug? So should be darker. Preferred the plug colour before but a shade lighter.

You mentioned slide. You have something fancy? Will go better with the stock 04, cut out under and pockets on the top. That might be the mid splutter fixed.

Dyno chart still not so good. This would really fly with a real fat expansion (think pipedesign).
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 12:06 pm quote
I believe this is the same slide you are suggesting. Cutout underneath with pockets on the top. It's listed as #4 side. Will try back 2 sizes up mj to 138 and compare.

I've thought about a pipedesign pipe but am not sure i want to go that route yet. I'm concerned about the volume. I do have a pm tuning pm20 exhaust i can try, but need to get the mounting hardware and silencer for it. My exhaust choices really center around trying to get as much performance with least invasive sound for neighborhood late night driving. I do realize this is nearly impossible to solve on a tuned two stroke so the road xl is kinda the middle ground.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2134
Location: London UK
Wed Jun 03, 2020 12:24 pm quote
If you are confident in your CHT gauge and have a stock 04, try an experiment. Reduce the main until the 3/4 splutter goes. Might still be so rich it's overheating at the plug. See how it feels but don't go thrashing it. Just to see what jet stops the splutter.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 12:44 pm quote
I think i need to bracket it. This was basically my plan of attack next. Gonna try 2 up at 138 to see if it gets better or worse to confirm going down is the correct direction, then try one down 130 and see if it gets better or worse.

I'm trying to adopt a method of confirming leaner is the correct direction before doing it by going richer first to make sure it gets worse not better before going leaner.
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1422
Location: california
Wed Jun 03, 2020 1:03 pm quote
Swiss - yours is a good approach in my view.
However would highlight one thing from Jack's comments.
Don't thrash.
Instead - focus attention to worst sputtery spot (3/4 throttle I think?) and see what happens there when you make changes up and down - rather then revving it out as hard as you can in second...

Also - throttle position can be tricky to identify when you are riding.
SoCal gave me a great one.
I am posting it here. You can look at your slide and confirm that the positions match - and it will allow you to report back much more accurately once riding.

IMG_1949.jpeg
Courtesy of SoCal Image Studios

Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 1:42 pm quote
Just read your page 1
Are you still running the Malossi 166 kit and si24?????
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 1:44 pm quote
Yes. 1st oversized.
Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 1:55 pm quote
swiss1939 wrote:
Yes. 1st oversized.
Ok what plug is that, looks es type, cant tell from photos but should be hs, it's the oil on the threads I'm looking at.
If you havnt read my setup here it is from my memory. All just bolt on.

Vespa px125 2009
Sip fast flow tap Mk1

Malossi 166 kit
22 tooth cosa clutch
Mazzi race cut std length crank
Sip flywheel
Sip race flywheel bearing
Sip road xl exhaust
Ngk short reach resistor 7 plug (HS)
Si24 carb
127 be3 160
Std malossi idle jet
Air filter drilled no gauze
Ovel hole blocked
Ducati cdi
Matching stator
Timing 18 degrees

Rides a tad rich bit superbly well.

I've been looking at variable ignition not convinced at moment. Still researching.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 2:04 pm quote
It is an es. Somewhere about page 10-15 we went through this someone suggesting it is supposed to be a short reach not a long reach. I've confirmed it is a long reach from the manual and visually checking with the head off. Short reach plugs are buried inside the plug hole. Long reach plugs are correctly seated just at the end of the plug hole without sticking out into the squish. Which malossi 166 head are you using? This is a mkii head. I'm wondering if the older malossi 166 kit heads used short reach plugs.

You are on rotary valve cases right? I see you are on a 160ac which is good for the rotary engines. Jack has suggested that lml reed valve engines have more draw of air due to reed valve, hence the need to go to a 120ac on the jetting.

Regarding variable ignition, I'm still a noob with all this but my understanding is it runs cht a little cooler overall because the timing is corrected for each rpm range which means the compression is adjusted for that rpm and by nature the temps get a little more stable. With that said, make a mistake in the wrong direction on this and you will have a paper weight fast!
Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 2:19 pm quote
swiss1939 wrote:
It is an es. Somewhere about page 10-15 we went through this someone suggesting it is supposed to be a short reach not a long reach. I've confirmed it is a long reach from the manual and visually checking with the head off. Short reach plugs are buried inside the plug hole. Long reach plugs are correctly seated just at the end of the plug hole without sticking out into the squish. Which malossi 166 head are you using? This is a mkii head. I'm wondering if the older malossi 166 kit heads used short reach plugs.

You are on rotary valve cases right? I see you are on a 160ac which is good for the rotary engines. Jack has suggested that lml reed valve engines have more draw of air due to reed valve, hence the need to go to a 120ac on the jetting.

Regarding variable ignition, I'm still a noob with all this but my understanding is it runs cht a little cooler overall because the timing is corrected for each rpm range which means the compression is adjusted for that rpm and by nature the temps get a little more stable. With that said, make a mistake in the wrong direction on this and you will have a paper weight fast!
I've no idea to be honest what Mk my kit is. I have 2 heads which I swap over from a decoke point of view, with my kit its definitely a HS plug, are you sure? Those threads look oily as if sticking out.
I'll have a look when I finish work.

The bit of research I have done on the ignition suggests that It increases heat. My draft conclusion is variable adds nothing to the top end on cdi scooters as I'm sure the curve i chose that suited my scooter riding style said 18 degrees was the optimum at speed. The benefits where tick over and acceleration but the down side was more heat as the engine was always at optimum burn.
Could be wrong only spent an afternoon on it.

Been out of the scene too long, your talking to a person who only discovered recently that malossi make a 177 kit now🤣
Enthusiast
Px125 2009
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Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 2:22 pm quote
I just recently read regarding reed verses rotary that rotary is better as a reed valve has a lag and are quicker to close.
Forgot to add that
It's all very interesting to see different approaches.

Time for me to work!
Night
🖐👍

Oh I suppose the surface area will be greater on reed valves
I'll post more when home
Lots of info regarding atmospheric speed comes into play.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 2:24 pm quote
Here i found the posts regarding plug length.
http://modernvespa.com/forum/post2343037#2343037

Yes the heat doesn't disappear, it just shifts more towards the exhaust. So with more advanced timing that i started with, the cht reading was higher but the egt readings never even got on the scale my gauge starts at. After shifting the timing two degrees, my cht has lowered about 20-40 degrees and the egt readings finally start to show up on the gauge at the appropriate times.
Enthusiast
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Wed Jun 03, 2020 2:45 pm quote
....

Last edited by Darren.H on Wed Jun 03, 2020 3:22 pm; edited 1 time in total
Enthusiast
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Wed Jun 03, 2020 2:47 pm quote
....

Last edited by Darren.H on Wed Jun 03, 2020 3:23 pm; edited 1 time in total
Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 3:08 pm quote
Well confusion over.

So I've read your post and found you have the MK111

Ive then checked some UK reference sites and found only one that has a definitive statement.

So I would say you have an out of date or badly translated manual as its says short reach for all kits except the 210's.

But I found this from a UK supplier called Beedspeed.
Extract from:-
Head centering dowls and a long reach plug fitment optimise combustion chamber geometry.

Should be working, but that was really interesting!
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 4:35 pm quote
Like I said.. visually confirmed it with the head off by screwing the plug in and checking to make sure the threads don't extend beyond the threaded hole. I didn't trust the manual was accurate and since I had seized it and had it apart, it was an easy visual confirmation!

Appreciate the effort tracking down some legitimate confirmation though! You had me questioning it for a second.
Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Wed Jun 03, 2020 4:37 pm quote
swiss1939 wrote:
Like I said.. visually confirmed it with the head off by screwing the plug in and checking to make sure the threads don't extend beyond the threaded hole. I didn't trust the manual was accurate and since I had seized it and had it apart, it was an easy visual confirmation!

Appreciate the effort tracking down some legitimate confirmation though! You had me questioning it for a second.
All part of the fun
👍
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Wed Jun 03, 2020 4:49 pm quote
In the same way that the CHT and EGT are a pendulum we are trying to even out, I believe my jetting is slightly off balance. MJ I feel like is a little too lean and idle jet is still a bit rich. Plug on a short low throttle run down the block shows way rich. So I have the 138 MJ back in waiting for curfew to end tomorrow morning to go run with it and see if it clears up the top quarter throttle bog. If it clears up a bit then i'll start working upwards instead of downwards.

I am planning on doing a series of bracketed jets and see what the dyno results are.. bearing in mind not to thrash it. I've been good about it so far as the memory of it still burns.

IMG_20200603_200939.jpg

Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2134
Location: London UK
Wed Jun 03, 2020 10:30 pm quote
Thinking 138 is going to be even richer but give it a try. That is seriously rich low down, which must follow on to the top.

Won't know if the timing is correct until the plug has a better colour but moving it the correct way so far.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 9:28 am quote
I believe my hunch that main too lean idle too rich pendulum in the middle needs to swing higher was right.

Yesterday: 45-140 idle 2.5 full turns out air mix. 120AC be3 132MJ

Today: 45-140 idle 2 full turns out air mix. 120AC be3 138MJ (1st run). Felt more powerful up top, but has a decent bog spot at 3/4 throttle which gets a little sluggish but clears up at high RPM. Tested the choke pull at WOT trick that MJ reminded me of and it slowed down a bit but didnt bog to a halt. removing choke and it took off faster again. Although there was cleaner acceleration throughout, there was a decent splutter at mid rpm on acceleration.

This led me to leave the 138MJ in and turn the air mix screw down some more from 2 full turns to 1.75 full turns.

Today: 45-140 idle 1.75 full turns out air mix. 120AC be3 138MJ (2nd run)

This woke up the bike more and seemed to clear up both the mid rpm and 3/4 throttle bog. The 3/4 throttle bog is still there but cutting the air mix screw leaner seemed to help. Bike runs stronger on the 138 MJ than on the 132.. albeit not as peaky rpms.. but close. It feels like it needed the extra gas up top.

Left it at that setting and drove around for over an hour another 40-50 miles then pulled the plug to check. I believe the 138MJ is the correct MJ but the idle now that air mix screw is sub 2 full turns is telling me the idle is still too rich. I think if I go down the next idle size (maybe and a BIG maybe 2 idle sizes) and get it to hit the air mix screw target of 2.25-2.5 full turns then this should clear up the stutter mid rpm and the bog at 3/4 throttle. I believe this is the way to proceed because the temps really stay sub 250F on city driving now and higher rpm longer runs that I am starting to test the waters with it stays around 275F and shifting to neutral for idle at red lights it still drops relatively fast. not super fast but noticeable cooling which is good. So this makes me believe the idle still has some wiggle room to go slightly leaner while still providing appropriate cooling. That and the plug at WOT still looks a little grey but moving slowly towards a more appropriate color at 138mj. So I feel the way forward is to creep the idle leaner and stay at 138MJ or creep it slightly richer as the idle gets leaner to 140MJ. Temps really feel are under control at this point as idling it cools, pulsing the throttle without taxing the engine cools it off, etc. Right now this jetting hypothesis seems more about fine tuning to remove the little bit of stutter/bog and hitting the correct plug color!

Just got a bunch of new plugs BR9ES for those who were wondering. So I will start anew with fresh plug now on this next bracket:

38-120 idle (3.15). hopefully 2.25-2.5 full turns air mix. 120 AC be3 138MJ.

If doing this pendulum swing leaner idle doesn't clean up the 3/4 bog then i know 138 is just sightly rich and 135 is the target.

As a sidenote, fuel economy has greatly improved! Im thinking it might be around back to normal if the jetting lands in close proximity to where it is now or next step mentioned above.. possibly mid to high 40's or low 50s fuel economy. This scoot had a 40-130 idle jet when I first got it before doing any work to it. So right now it looks like I am only 2 sizes richer, and going down to 38-120 would only end up 1 size richer than stock if that works out correctly.

22tmark_138mj_45-140idle_1.75turnsairmix.jpg
pretty positive these gsf dyno graphs are more ballpark than accurate. this one says I have more power but less rpm than before. I guess that could be right the way its less peaky but felt stronger.

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Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Thu Jun 04, 2020 10:25 am quote
So the idle jet doesnt really effect anything above say quarter throttle.
The fuel passes from the float bowl, through the main jet then through the idle jet, down to the progressive hole ( in the slide groove) then to the idle mixer.
At higher air speeds the flow of fuel reduces from both as its drawn from the brass tube poking into the venturi as that's the easier passage

As atmospheric speed increases the quantity of air decreases. Big hole in the ac slows the atmospheric speed down, increases the air content runs leaner.
Ruffly for every part atmosphere drawn over the fuel puddle 1 part fuel is drawn. So the mixer tubes if you look at the size and placement of holes the higher up requires a greater airflow to influence fuel drawn. The larger the holes the greater the fuel that allows a person to work out which one to use, but just about everyone except T5 owners runs 160 ac Be3 then chosen mj.

Tbh with that main jet stack being so so rich and showing optimum colour on plug it would point me to look for an air leak.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 10:29 am quote
My 138 mj is a measured 131mj. Labeled is off from actual. And this engine was pressure tested.
Enthusiast
Px125 2009
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Location: UK West Yorkshire
Thu Jun 04, 2020 10:40 am quote
I hear what your saying but you are incredibly rich. You couldnt do much more to make it anymore so.

Unless your atmospheric flow is incredibly slow through the carb and into the crank its pointing to an air leak.

Usual suspects are carb base to tray, then tray to engine.did your pressure tests happen with these items removed?
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 11:34 am quote
I didn't like the 38-120 idle. 138 maybe too large still boggy. Gonna go back to 135mj and either 45-140 or 40-120 idle to see if i can clear that low end stutter up. 38-120 felt too lean. 45-140 felt just right with some air mix screw fiddling. You may be right I'm too rich but I'd rather test these by going too far to confirm its rich which is what I was trying to do.

Pressure test was done with a rubber toilet bowl gasket sandwiched between the reed plate and carb box.
Jet Eye Master
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 2134
Location: London UK
Thu Jun 04, 2020 12:00 pm quote
You're starting to do what you did last time. One thing said was correct, the pilot jet has nearly no affect on 3/4 throttle, so stop thinking about it. And the mixture screw only effects the beginning of the pilot, so even more irrelevant.

Focus only on the main jet. Main jet and nothing else. When there is no splutter above 3/4 the main jet is close. Looking at that plug and how it's performing, it's way too rich. Maybe 10 points. Put in a 122 and see how it goes, without holding open for too long.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 12:53 pm quote
Ha yeah you know me too well now. Will be extremely careful with that one and see where we land.
Molto Verboso
Honda elite
Joined: 19 Jun 2007
Posts: 1036
Location: California
Thu Jun 04, 2020 1:08 pm quote
In my case sputtering with a 135MJ gone with 132MJ currently testing with 122.

If you focus your testing to a WOT in 2nd gear beginning at a low RPM you should quickly discover which jet runs clean.

The as measured stuff seems irrelevant and difficult to follow. Stick with a brand set/range the size printed might only serve as reference.

DE25ADA3-7110-42E7-8E35-89D4DD09D191.jpeg

Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1422
Location: california
Thu Jun 04, 2020 1:19 pm quote
Swiss - for what its worth:
Mine too landed at about 120 MJ (120AC/BE3).
Cylinder is a skeleton of its original small holed self.
Inlet is opened in all directions - tho not reed like yours.
Pipe is a box pipe (SIP Road II)
Carb is almost identical, and had a 2.0 hole in it (I have another with a 2.3)

If I am following - you currently have both CHT and EGT gauges - so certainly keep an eye on them and don't go for a 2 minute WOT uphill with a back pack on 4th gear run...

yet...

but if Jack is right on richness, hang on to your hat - cause it is gonna make a whole different kinda noise and pull with a leaner jet in there.

-CM

Edit: Hibbert - what jet did you run going up the hill before you went to the leaner one when we were climbing?
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 1:30 pm quote
hibbert wrote:
In my case sputtering with a 135MJ gone with 132MJ currently testing with 122.

If you focus your testing to a WOT in 2nd gear beginning at a low RPM you should quickly discover which jet runs clean.

The as measured stuff seems irrelevant and difficult to follow. Stick with a brand set/range the size printed might only serve as reference.
Hibbert, I've seen that graph and my measurements contradict it. Sip on that graph are same labeled and measured. Mine are . 07mm smaller. I have been sticking with labeled sizes when talking jets unless i specifically say measured. Will avoid mentioning measured from now on and stick to manufacturer labeled.

Cm, yes when i go down to the much leaner size Jack suggests i will most certainly not run it hard but be extremely nervous about it and baby it. I've been avoiding going leaner to be extra cautious but Jack has continually been suggesting it's over heating from being too rich main and throwing the plug color off. The reason I've been hesitant to go lower is the temps are very close now which makes me want to believe the main Jet is close at the much richer size.

I guess there is no more avoiding it and it is time to go leaner on the main.
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1422
Location: california
Thu Jun 04, 2020 1:38 pm quote
I was just trying to bolster some confidence to follow where Jack is leading you.
I have a not dissimilar build, and nearly identical carb.
The biggest effect on mine for MJ size was hole size in carb.
At 2.3mm, I was down around 114MJ!
At 2.0mm, I was at 120MJ

So go rev it out!
Start at 10MPH and open it up and let it roar.
Just don't sit on it at WOT when you get to max RPM for too long without keeping close tabs on those temps you have gauged.

My guess. It will actually stay quiet cool at WOT - its the 3/4 throttle under lots of load that will raise temps. Thus my uphill with a backpack comment.

Caveat emptor: you have reeds - which perhaps make it more thirsty than mine - but your build is otherwise similar - so 138 seems mighty large.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 1:47 pm quote
Yes the encouragement of you guys swearing your similar setups are much leaner is making it less daunting. Appreciated.
Enthusiast
Px125 2009
Joined: 31 May 2020
Posts: 57
Location: UK West Yorkshire
Thu Jun 04, 2020 1:49 pm quote
Can anyone explain the logic behind a 120 ac?

And to nail the idle jet,
It feeds the progressive circuit which opens very early once above that the idle jet adds very little to nothing as the fuel flow wont go two ways.
It's as simple as knowing water takes the easiest path, so the fuel leaves float bowl then into main jet, rises then passes into the idle jet base, once the effect on the brass tube within the venturi is starting, the fuel follows the easiest path.
On tapered needle carbs once the main kicks in the flow of fuel in the progressive circuit is reversed, so fuel doesnt flow out, air flows in.
Just thought I'd chuck that in.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Thu Jun 04, 2020 2:04 pm quote
I'll let one of these other guys try to explain the 120ac stack. I'm just along for the ride. And very hesitant to lean this out.
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