Modern Vespa

I am still getting this "four stroking" at bottom quarter throttle which seems to happen on the transition exactly between the transition of bottom quarter throttle and everything above that. It happens both on throttle up and throttle down past that line. Is this just a normal carb that happens even when perfectly dialed in?

I've attached an audio file I clipped off a few examples separated by silence to get some opinions. First sound bit is me holding throttle exactly on that spot for about 8 seconds, next two short bites are when it happens at throttle up, first really quick throttle up, then slower throttle up. Final bite after the last silence spacer is 30 seconds of somewhat normal driving where i am holding throttle at the four stroking spot to exaggerate the sound for you to hear the "four stroking" every time I throttle up or down past that first quarter line.

Am I even using the right term of "four stroking"?

https://drive.google.com/open?id=1mrcjXFfoV06O_Fp_u8GORuXfLSHACufe

This was all recorded with the current jetting of 40/120 idle at 3.75 half turns out and 120/be4/97MJ.

Along those same lines, this is what I experience currently on 40/120 and more pronounced at 45/140 idle jets. When I hold throttle at the exact spot where I get that "four stroking" sound for extended time, then jam on the throttle to wot as fast as possible, the bike sort of hiccups with a quick loss of acceleration then a fast surge forward. I'm thinking it may be fuel tap related? Maybe because I do not have a fast flow fuel tap, that four stroking sound is the fuel tap struggling to provide enough flow, and the sudden surge of throttle pushes the tap to its limit so there is a moment where there is not enough flow from the tap, and it catches up after a second?

Here is a sound clip of it.. where I jam on the throttle is where the bike kinda dips in power for a split second then surges forward where my theory is the fuel flow catches up with the throttle change.

Again, its probably just normal functionality of these bikes, but I am trying to understand if it is that or something else not right about the jetting.

https://drive.google.com/open?id=1eXmzM5lzX9oIbZLx8lpbxnlUXnzn96Gx

Finally for today, here is the plug after a not so long WOT run.. held it at full WOT once it reached its max for probably 2-3 seconds.

EDIT: I actually decided to go back down to 45/140 after this to run it for a while and check plug again cause I felt it was running better with better idle than the 40/120. Strangely enough, when I went to change the idle jet back to 45/140 I just happened to notice that one of the two screws for the float top half was completely loose. Tightened that down and then also tightened the other one down in case it was thinking about wiggling out. I don't think anything was affected in jetting from that cause I couldn't see any leaking at the seam where the gasket edge is. It was too late to go running around with the tightened screw and new idle again, so I will take it for a ride tomorrow and see if anything changed as a result of the tightening.


WOT Plug check: 40/120 with 3.75 half turns out. 120/be4/97 MJ.

WOT Plug check: 40/120 with 3.75 half turns out. 120/be4/97 MJ.

WOT Plug check: 40/120 with 3.75 half turns out. 120/be4/97 MJ.

I think I finally set up GSF Dyno settings correctly as I found tech doc for the SIP tires I have with specific tire circumference, and also calculated the correct gear ratio for my current setup with 22 tooth clutch.

Just under 15 HP from PNP Malossi 166 MK III kit with 40/120 idle and no O-tuning, which lines up with Malossi's brochure listing this kit as having a power range between 14-22 HP. That's about a 60% increase in power from stock.

14.41 PS / 7117.59 RPM
14.81 Nm /6645.5 RPM

Max RPM 9718.86

This was in 2nd gear as I can't run a test to record the audio in higher gears on back roads anymore cause I'd be flying way too fast! I should theoretically top out at 69-70MPH from the scooterhelp calculator, but I have yet to get there.

Current stella setup:

166 Malossi MK III PNP
SIP Road XL Pipe
Boyesen reeds
22 Tooth Clutch


Malossi 166 MK III PNP. 40/120 idle. 120/be4/97 MJ.

I have the same 4-stroke issue at low RPM. Never could get it figured out 100%

When I switched to boysen reeds and a cut out carb slide it seemed to help.

I have boyesen reeds in this, but not a cut out carb slide. I do have a 24/24 SIP carb with the fuel supply hole drilled wider and a cut out carb slide waiting to be installed, but I am gonna keep that for when I finally o-tune the cylinder and case. Also have a fast flow tap waiting for then.

After about 60 miles running with this 45/140 idle jet I had in it before the upgrade and I've mostly gotten rid of it except for very tiny bit of it right at the transition point. The 45/140 idle jet is the winner for now. I think it may still be just slightly too rich as the air mix screw is 1.3 full turns out, under what it should be at, but I'm gonna leave it there cause it is the closest ive gotten it to perfect so far, and I'd rather be slightly rich for a while. I may even need to come down 1 or 2 points on the main jet like Jack suggested originally, to a 96MJ. I think going to 96 would bring the air mix screw setting up into good range and probably take care of that last tiny bit of four stroking.


45/140 idle. 1.3 full turns out air mix. 120/be4/97 MJ.

45/140 idle. 1.3 full turns out air mix. 120/be4/97 MJ.

I think it may be slightly rich on the main jet, thinking it could go down to 96 or 95, but it runs great the way it is now so i'll leave it.

The updated dyno results with 45/140 idle jet that is pretty close to on point shows a slight increase of almost 1 HP.

15.14 HP @ 7122.68 RPM
15.08 Nm @ 7018.36
Max RPM @ 9740.91

Got it up to 67 MPH again.

When I took the plug out to check and get a photo after that 67mph extended WOT run, the blazing sun was at the right angle to shoot straight through the plug hole into the cylinder so I could see it easily. What a nice amber beer color the cylinder walls have with this jetting!


the cylinder walls look like this with the glaring sun beaming into the plug hole!

45/140 Idle. 1.3 turns out air mix. 120/be4/97MJ. Strong WOT run.

45/140 Idle. 1.3 turns out air mix. 120/be4/97MJ. Strong WOT run.

Pilot jet is too weak. Thats what the hiccup at 1/4 is. If the Malossi supplied 52/140 is too rich on the screw, then 45/120 is the jet you need. Often guys think this is too rich and 4 stroking but its actually weak.

Are you running with an air filter? Might be time to get a Vortex.

So what you are suggesting is to provide way more air to lean out the correct idle jet, then adjust main jet appropriately? Cause 52/140 is way rich right now and 45/120 would be even more rich in terms of air mix screw. I'd barely be turned out at all. Thing wont stall with the screw completely closed at 52/140.

It does not do the hiccup right now at current jetting, but there is the slightest four stroking on the transition point.

It seems what you are saying is that the idle jet is what everything else should conform to.. so keep that as close to manufacturer spec as possible, and then conform everything else to that. What about changing to a 160 AC? We went down to 120 AC which made the main jet stack more rich, then down on the MJ to compensate. But if its still too rich and interfering with my ability to use the correct idle jet, then shouldn't I be going to 160 AC or 185 AC to really lean out the main stack. Then I would be going up to what seems to be the suggested 105-115 MJ, and probably be able to go up to the correct richer idle jet since the main stack won't be flooding it?

If I were to go to a 160 AC, it seems that I would need to use a 128 or 130 MJ to get back to approximately the same richness level (solely on the MJ stack) that I have now, and if I were to hit the same overall richness of both jets, then a 115-120 MJ would get me close.

So that would be trying this in order to potentially use the correct idle jet and correct for the low end fuel flow issue causing hiccup/four stroking (instead of spending more money and buying a vortex just yet):
52/140 idle
160/be4/120

I am also inclined to think this 160 ac may be correct as the Malossi instructions say 52/140 idle and 105-115mj with "original" air corrector. I assumed that original meant the original one to my bike. Stella has 140, but px has 160. So I think they may have meant 160 AC.

Give it a try. Might blow up, might not

45/120 is going to be about right about right. If not exactly right.

This is at 52/140 1.25 full turns out and 160/be4/107. I started at 120 and worked down to this. Gonna go to 105 now. It runs almost exactly the same as the best before with maybe sightly less four stroking in lower third. It does seem to putt putt better at idle speed now.. More consistent.

And with the 160/be4/105 the bike finally dies when the air mix screw is closed all the way. It's at 1.3 full turns out now. Going to check plug now.

I can see you want to try this yourself. Just keep your hand over the clutch.

This is it at 105mj. I have been keeping my hand over the clutch this whole process as I'm not sure about anything. Just responding to what the bike and plug shows me while trying to digest what you are telling me to do into understanding on why and how to make these changes which I definitely appreciate. Just not ready yet to throw another variable into the mix with a vortex instead of air filter.

Tell me if I am wrong that I cannot make the richer idle jets work without making equal and opposite changes to the main stack which affects how the idle jet and air mix screw are set. I just don't see how going to the idle you say I need to be at can be done without leaning out the main. Going richer on one thing while staying the same is only going to make everything too rich and flood the plug as I was doing originally.

52/140 1.5 full turns out. 160/be4/102 WOT run.

At this setting the 52/140 idle dies at less than half turn out and more than 5 turns out. This was never the case with any other idle jet and mj settings before on this. Could not get it to die with this rich of an idle jet previously in either direction.

I mistook Jack's suggestion to use a larger carb for a suggestion to use a Venturi adapter on the current carb instead of the air filter. Which is why I took that to mean go leaner on the main jet to get a richer idle to work.

It may be time to stick the 24/24 carb I have on this bike.

If you do long WOT runs on that 102 it's going to seize. The AC160 and BE4 are not supposed to go together. There is too much air for the atomiser.

An LML is not a Vespa. The stock rotary inlet is not open for so long compared to LML reed duration. The jetting will end up different because of this.

Put the 24/24 on when you do the 60 crank. Jetting will not be so much different form the 20/20. This work won't be wasted.

If you leave the air filter off and run without one while getting the jetting to work it will save time.

Good to know about the reed vs rotary differences in terms of jetting requirements. I was thinking about leaving the air filter off to save time, but was not sure if that would mess with the mixture of the jetting. Will do that from now on.. as I have probably removed everything and put everything back in the carb to change jetting around 100 times in the past 3 weeks now. I feel like a pit stop crewmember.

Regarding the 160 AC with be4 atomizer, how does the larger ac affect the be4? Is there a chart somewhere that shows which atomizers go well with which AC's and which do not work together? I would never have known that if you did not mention it, which is why I figured it was no different to go up on AC to move the pivot point of the seesaw of richness between both jet stacks closer to the idle jet in order to bring the MJ up higher, since I have main jets up to 128 that I could work down from. In that case, I've ordered the idle jet you suggest is best for reed valves and a bunch of smaller main jets down to 84 so I can work down with the 120 AC.

Hey Man, sorry im so late to the party but what stack are you running in this sound clip?

Here is my setup.
This is the famous "Bald John jetting" that is supposed to be the best main stack to run on many kitted bikes, minus the main. that's the one to play with for full throttle.)

160 Air Corrector
BE3 Mixer
120 main!<-- Which seems insane for my setup.


Stock stella long block
Sip sport 2.0 with the long chrome pipes.
px200 filter (pre drilled heart)
GGR Hot Reeds, (Polini red carbon with gutted center bar)

I have Zero 4 stroking, Great response, great idle, great mid range.. and im a big fat fuck so im almost pulling a Euro Pillion weight wise. lol

The only issue I have is if I start the bike up to warm up for like 5 minutes while i get my helmet and gloves, etc.. It seems to load up a little bit and at the end of grabbing 2nd gear out of the driveway it cleans right up and runs really great.

What stack are you currently running?

Hey deathshead, because I am not on a stock cylinder anymore that jetting won't work for me. Appreciate the suggestion though! I've been trying to get the jetting correct based on the malossi instructions and with the help of everyone here. Best I've got so far where it ran great although I'm told the idle was too lean so now I'm trying to work the main down to match the idle. I've got it running well on both ends of the spectrum after today, with the idle too lean and main just right, and then also with the idle just right but the main too lean, neither will do long distance highway driving safely. When it runs great at either end of the spectrum it has plenty of torque and revs to 8-9500 under load with around 14-18 hp, so I know it will be good when the jetting is worked out appropriately.

I've got richer idle and a bunch of smaller main jets on way to hopefully nail down the correct settings where both stacks are just right. Expecting everything next week due to holiday this week.

I hear ya 100% - But if you look up Bald John's jetting on google even when he was doing alot of dynoing on alot of different kits, he still reccomended that basic main stack, - just minus the main jet changes.. Lemme see if i can find some of his info for ya real quick.

"What your jetting should be on a "stock" Stella:
160 Air Corrector
BE3 Mixer
100 Main Jet

Also, this is not surprising. This is the main Stack Vespa used before emission regs. Get it?
__________________________________________

This jetting is for stock Stellas and fully tuned and hotrodded engines. The only thing you need to change is the Main Jet and the adjustment of your Idle Fuel screw found behind the teflon plug at the rear of your carb box."



Edit: this was just a copy/paste from the ggr reeds Facebook as one of their suggestions for stock and also kitted bikes.

Last edited by Deathshead on Tue Jul 02, 2019 1:03 pm; edited 2 times in total

https://drive.google.com/file/d/0B_DPw3uQ-pu-WWhaek94d3BxQmM/view?fbclid=IwAR1zRoH7ciM-jTE7yzGooiPK-wPqg7mQPqdpaSwNYE_Kvkqcue5i3RQKN2I

Just pointing out something I noticed.. on page 50 of that article, He is comparing his reeds to stock and boyesen reeds, and you are provided an image of all 3 reed blocks upside down. The GGR hot reeds block has the middle bar ground out and the opening widened, so obviously there would be better performance of ggr hot reeds when the other two do not have the center bar ground out or port widened, thus affecting airflow. I know the stock reed pedals can't have that bar ground out, but you can do that with the boyesen reeds, and I bet if you did a fair comparison of the boyesen reeds using the same optimized reed block as the GGR, they would be equal. So its not really a testament to those pedals being better, just the block being optimized on that one.

I'm in too deep in my process. Almost there with what I got. Not starting over with another jetting style when this one is almost there.

But I will leave you with this for now:
https://www.youtube.com/watch?v=XcATvu5f9vE

I am looking at Bald John's theory of jetting and I can see how it could work and makes sense as an alternative to the standard jetting on si carbs in that you are using 2 variables instead of 3 (controlling the correct flow of fuel between the idle mix and main jet to work across the whole spectrum). I'm sure it works if I took the time to work through it and set it up right, and I may try that some day. But right now, I am trying to learn how to jet the way that SI carbs seem to be intended to be jetted, given that they have various sized idle jets. I'm gonna assume they knew what they were doing and there is a reason you want to change the idle jets, and if they intended 55/160 to be the only idle jet, then there would be no others.

Jack seems to have suggested reasoning for that being different idle jets provide different fuel flow rates or something like that when he mentioned that reed valves have a stronger "pull" or flow rate requirement than rotary valves due to the less restriction at the crankshaft inlet from the carb.

I'm sure this is already a hotly debated topic with proponents and detractors on both sides. I'm pretty willing to go in any direction as I can see both methods working. My choice simply comes down to the fact that I have spent so much time getting it close and am starting to slowly see/understand how it all works in this current method, that to completely change the process would be unnecessary.

I think If I can dial it in correctly with this current process I am almost done with, then I bet I could work out the equivalent jetting in bald john's method using the known factors from my final version in this method! I've got an extensive excel spreadsheet recording every change I make and the results. It would only take some excel functions to compare the differences between one style to the other.

I may even just try it for a quick run, once I finish this, to test that theory!

Regardless, as I wait for the jets I ordered to continue with this current process, I finally got a replacement temp sensor and stuck it back on the spark plug. I am currently at 48/140 idle and 120/be4/95 MJ and the bike rides between 230-270 F and at red lights it starts to cool off almost immediately and pretty fast compared to my jetting on stock engine.

Now the temperature gauge is working again, if you are only getting to 270F at WOT then it confirms what you are seeing at tickover with the mixture screw closed. The main jet is still too big. 95MJ is quite small but this is an LML with a 20/20 carb and reeds. Plug is still dark, mixture screw doesn't cut out and the temp is low. Main jet is too big. Go down another 5 to 90 and cautiously see what happens. The 48/140 will be too small at 1/4 but 45/120 should fix that.
Are you running without the air filter now? Some of those fine mesh filters are really restictive. If you have one of those new type ones it will be causing this entire issue.

That was not temps at wot, but City driving mid range, although I expect it should be cool at wot. If I give it a ton of gas the temps drop, it's only when I hold mid throttle where temps slowly climb and not even that high.

I do have the blue air filter. I will remove it when the rest of my jets come and I work down from 95. I just threw this jetting on for not so I could ride in meantime, cause it's closest and safest jetting I have available.

Some think no filter is as good as a vortex. Should improve your situation.

Need some temp data from a wot run when you're ready. If you do it with the air filter off it will be more accurate.

^ I’m in this camp ^

hello,
i dont know if you've tried or may consider having a go with a BE3,...????
when trying to sort my 166, i found when using the BE4 it was always a pig,..
mine is fine with the BE3 ,..but likes a fat idle jet,....
I believe malossi really wanted to cover there asses regarding the BE4,..
sorry for butting in,...
pek

Swiss - good stuff. Jetting excersize has been interesting to follow.

You probably already know - but felt worthy of posting: if you deblue or remove air filter - it will be like jumping down 1-2 jet sizes I would think.

U might want to do that with current jetting prior to dropping in the new smaller main. Otherwise you maybe taking a larger than expected step leaner.

Think of it like a free new main jet.
Total removal of air filter might lean further. [/quote]

Ok so I keep getting confused by what you mean of vortex. Originally I thought you meant this:
https://www.sip-scootershop.com/en/products/air+intake+system+polini+ve_20301520

then I thought maybe I was wrong and you were talking about just a specific carb.

Now I realize you were talking about the first thing, a venturi adapter to create better flow into the carb.

I will definitely remove the air filter and run without it if that is considered the same thing as one of those venturi adapters. Saves spending $45 on something apparently not necessary! And yes, chandlerman, I will do this before going down from 95MJ.

I was out of town for the past 5 days and am working the next two. All the jets i've been waiting on were delivered while out of town and I am hoping I get out of work early tomorrow to work on the jetting some more before dark. I will run a WOT test with no air filter and report back the temps for you guys.

Took off the air filter, went up to the 45/120 idle (1.2 full turns out) and changed main stack to 120/be4/92. I maybe shouldn't have done the MJ at the same time as the air filter like suggested. I meant to change it to only 94 MJ instead of 95 but put the 92 in by accident. I think it is too lean as when i took it out on the highway connector I use to test wot runs, the 2.5 mi out to the other end it got up to about 360F. Then I got off the connector waited at light to turn around and it went down to 330F. When I got back on the connector for another 2.5 mi back it climbed up to high 360s and probably low 370s.. seemed like it was gonna keep going up so I backed it off. When I got off the connector at the return of the 2.5 mi run (5 mi back and forth), I pulled the plug to check. The first 4 photos are after the WOT run. It looks to me like it is too lean. I did get it up to 69mph which is the fastest I've ever gotten it.

The last 2 photos are of it after city riding back to my garage about 10 miles.. so mostly middle throttle. City driving it hovers around 250-270F, and drops pretty quickly at red lights after a very short increased blip in temp.

It's gotten a little more sluggish again in the low RPM range, not bogging, just not insane acceleration like when I had lean idle.


AFTER WOT RUN... 45/120 idle. 2.25 half turns out. 120/be4/92 MJ. No air filter

AFTER WOT RUN... 45/120 idle. 2.25 half turns out. 120/be4/92 MJ

AFTER WOT RUN... 45/120 idle. 2.25 half turns out. 120/be4/92 MJ. No air filter

AFTER WOT RUN... 45/120 idle. 2.25 half turns out. 120/be4/92 MJ. No air filter

CITY DRIVING RUN... 45/120 idle. 2.25 half turns out. 120/be4/92 MJ. No air filter

CITY DRIVING RUN... 45/120 idle. 2.25 half turns out. 120/be4/92 MJ. No air filter

Swiss,

Loving the detailed break down on your jet experimentation.

Since u have the blue filter - it is more significant leaning to go to no filter than say a std Vespa filter being removed.

Some of the guys jump as much as ten points on main jet as first move when putting vortex (aka bell mouth aka Venturi) on.

Perhaps filter removal isn't quiet that dramatic - but given the move from blued filter to no filter - it's probably meaningful.

PS. Chandlerman is the guy with actual legit knowledge and skill. I just play one on TV.

🙂

my bad charlieman! that chandlerman you play on tv seems to be in the news lately, so I got confused!

I got back to my garage and put the 95mj back on just for the time being, but did not run it with that yet. I will check back here tomorrow and when I get out early from work again and I'll take it for a ride with whatever main jet seems to be the safest.

I know your working with Jack on this, but just remember that a plug color at WOT for 2 or 3 seconds is a LOT different from a plug color at WOT for 20 to 30 seconds.

Wow. You were lucky. I can't believe you didn't feel it.

Now, don't get too stressed but that silver on the plug is melted piston. Only one run so expect no noticable damage. The piston crown does sort of atomise when they get really dangerously hot, then splatter silver particles everywhere.

What you should have done is stopped as soon as the temperature went over 320F. That is the limit. Remember that number forever. On the road 320F is maximum reliable power. More temperature is less reliable power. Will still go stronger if hotter but will either have a high wear rate or seize up; ie. not reliable power.

I said 'Some of those fine mesh filters are really restictive' but forgot how absolute crap they actually are. You need to up your main jet about 20 points to start. Funnily enough that is back to 115. Might get the 52/140 pilot running yet.

Edit. btw if that didn't seize up nothing will when down at 320F. Running in is officially over. Yay

Holy crap swiss... my 2 cents... you took that poor top end right to the edge running WOT with that dinky main jet and no air filter. You could’ve taken one for the team in a big way. Unless you’re deliberately trying to seize, you need to be at least up in the 120 range. FWIW, when I ran a bellmouth on my 20/20 (Polini 177) I used a 125 main.

Last edited by SoCalGuy on Tue Jul 09, 2019 4:45 am; edited 1 time in total

Yeah when I saw that spark plug tip I thought that might be piston damage. Hopefully I didn't do too much damage to it. It might have slightly seized for only a fraction of a second near the end of the run when I let off throttle cause I was worried about the temps. I was thinking 375 and higher were dangerous. Now knowing 320 is the limit, damn I was way over! It felt like it barely grabbed for a fraction of a second when I backed off throttle so I hit it with a little gas and it cleared up as I kept it at mid throttle to get off the highway and pulled over immediately to check plug and let it cool down.

That is good to know 320 is the limit and that it won't seize if running all day at correct jetting. I guess a damaged piston crown is better than a damaged cylinder if one of them has to be replaced, the piston is cheaper! I was wondering when I'd finally do some damage to this thing. Seemed to be pretty lucky up until this point!

EDIT: I will say that from an outsider perspective this may seem stupid, but I am learning a ton from this about what correctly set up carb sounds and feels like. I definitely felt like something wasn't optimal with jetting at this run cause it just seemed louder with more rattling at higher throttle. The bike didn't have as much deep powerful sound to it. I'm starting to learn what it should sound and feel like at the right jetting. I will go up to 120/be4/120MJ today.

also.. ironic that this was my 666'th post and now my rank says "evil". Seems appropriate for the content of the post! I guess I should count my blessings!