Modern Vespa

I have a feeling that mine is going to run hotter. I am not confident in holding her at WOT for long. The temps rise fast

The fastest temperature is 150C. About 130 cruising and 150 at WOT.

Mine is higher than that. Can reach 150 cruising and 170 wot. Jetting seems good though. What is the absolute max temp I should be concerned with, the point of seizing etc?

It's not an exact science, I had a kit that would soft seize reliably at 177°C, my current kit has been up to 183°C and not seized. Cylinder head design, spark plug and sensor placement all play a roll. I'm working at jetting to cool it down a bit, I like to stay around 150°C also.

Apart from not seizing, setting it up to be fast is the most important thing to me. This happens when just less than 150C under the plug. Anything over 150C is not as fast as it could be....even if running fine for over 10 years or more. Hot is not quick.

I think my temps in 4th gear are higher because I am never at full throttle. Always around a quarter to half. Just rinsed it in third at max revs for about a mile. Max revs in third were around 8000 before it felt like it was spluttering. Temps dropped to around 129 and dropped slowly at max throttle. I guess I am running slightly rich main jet but I am ok with that at the moment. Changed idle jet to 60/160 and 3 turns out. Feels and sounds better low end now. 4th gear at max revs was around 7900 rpm with temps in the high 130s and low 140s. I very rarely ride it wot. Runs better and cooler the harder I ride it within reason.

Is it normal for the bike to heat up more when in 4th gear and around 1/3 to 1/2 throttle? Got to 167 degrees C cruising at around that range. Was a bit hilly here and there.

No not good. Whats the exact jetting? Ignition Timing? Vortex, box lid? situation now?

120/BE4/135 60/160. No vortex. Lid fitted. Timing as retarded as it will go. AT I believe. Soon cools down when drop a gear. Just a bid odd.

Best to strobe it.

If it's set at AT, that explains a lot of your troubles

AT is what Pinasco recommend for that cylinder kit.

I'm sure they said that.. but I don't think that'll work mate…

23degrees at ~4000 rpm, in 4th gear… that's where all your heat will be coming from

I think scooterlab was mentioning pinasco got their timing instructions wrong and always best to strobe The ignition.

I think AT would make sense if it's a flytech (or variable ignition system…) but even then… it's probably off mark

It's set at 18 degrees. As far retarded as possible. I thought that AT was fully retarded.

If you reach 18deg, you'll be dremelling on a stock stator.

Sounds like this might be it. While setting up it the carb it needs to be exactly at 17 degrees (if static). Can change it later once you know it doesn't blow up but for now 17.

All marks on the stator/flywheel/casing are not accurate enough. They are certainly within +/- 10 degrees but can't be trusted.

Make your own marks with a degree wheel. Use a strobe light. There's a thread on here somewhere which explains it well.

So if my stator is as far clockwise as it will go, and is still too advanced, how do I retard it any more?

If its too far retarded it gets hot too. There's nothing easy.

LOL. OK cool. I thought only too advanced timing caused heat issues. I am on holiday in Spain now for a week. Only been here a few hours and I have seen loads of vespa. I shall take a look when I get home as I already own a strobe light. One thing after another.

Sorry, its set at IT. In fact it's set past this as far as it will rotate clockwise so it may quite well be too retarded. Bit like me.

If my measurements are correct, the timing was set at around 15 to 16 degrees btdc. I have advanced it to 17/18 degrees. See how it goes on the temp side of things. Didn't have a piston stop so had to use a screwdriver with a loose cable tie around it to guess tdc. Seemed to work OK. Piston stop on order so I can do a more precise measurement.

The engine sounds different since I advanced the timing and I think it's less powerful. Might just be me. It also appears that I still have a fuel supply issue as I cannot get the engine to bog down or stutter even with a 145 main jet. Bowl is drilled to 2.5mm. Idle jet size doesn't really change anything either. Going from 58/160 to 65/160 makes no difference at all. It's all very odd. I fitted a 180 jet that I drilled myself and the engine bogged down really bad so that rules out a fuel delivery issue. However, the atomiser (BE4) was clogged up with what appeared to be plastic? I have cleaned all the jets and now the bike bogs down bad on a 148 main. I guess its as case of working my way back down again now until the bogging stops. I have also noticed that when I place my hand over the underseat pinasco air filter, nothing happens. The engine ildes and revs as it were not covered. Air box seal and snorkel arrangement are fine and fitted properly. Hmmm?

Let's call this topic closed. Clearly an issue with the bike that nobody can solve. I will just ride it until it melts. Thanks for all you help.

Sounds like you're getting somewhere now. Until it bogs at WOT the rest of the jetting can't begin. If the WOT bogging stops and begins to rev out to max rpm at between 130 and 135 main, while still on AC120/BE4, then it's all good.
This is all while the vortex is fitted, box lid fitted and bellows to frame. There should be no air filters anywhere at this stage. Remove all of them.

Good morning. What are the max revs that I should be aiming for with this setup? I have removed the vortex as with it fitted, I cannot get it to bog down unless I fit a massive main jet of around 160-170. These jets I drilled out myself as I did not have one big enough. Something odd is going on. Without the vortex I have been running with a 135 or 138 but it sounds odd. Not pinking but really crisp and just weird. No hesitation or bogging. If I hammer it WOT in 3rd, temps rise to around 130-140 C but then start to fall. This is on flat ground. Any incline raises temps a bit. I am giong to check my jb weld job today with some carb cleaner. I will also check the area around the carb just to rule out any air leaks. Timing is now set at 17-18 degrees btdc.

Seems to run fine. Stutters now and again so I think it is a bit rich. Running a 140 main until it goes on the Dyno Wed. Sorry about the camera rattle. Annoying.

Doesn't sound so bad. It's way rich but sounds good. At this stage the only relevant bits are when at WOT. There was an open in 2nd in the middle of the video. How high was that rpm? Sounded spluttery. Think the 140 is too big.

Hi. The RPM in second was around 8500 when it revved out and did sound spluttery. It's defo rich. Taking it to dyno on Wed. The main will be probably what you said way back on this thread, around the 130 mark.

Is this a bit too lean? Also, looking at the attached atomiser chart, I am using a BE4. This is lean at the top end. Would it be better to use a BE3 that is rich at the top end when going from WOT to zero? Just asking. I don't understand how they fully work. When riding the bike today at WOT in 4th (really heats up but only in 4th), I am sure it's soft seizing. The back wheel does not lock but I can feel some weird thing happening as I lunge forward a bit like pressing the brake for a second or so. And finally changing the idle jet has little effect on idle. Changing from a 55/160 to 65/160 behaves virtually the same. The engine revs a lot higher when the mixture screw is fully closed but even when opened 0.5 - 4.5 turn out, the revs drop but don't change much after the initial 1 turn out. This is very odd and driving me a bit mad.

This chart is misleading and definitely translated. Its trying to mean the BE4 is richer at the bottom and leaner at the top. The top of a BE4 is exactly the same as a BE3, so not any leaner, just leaner than itself at the bottom. Probably makes perfect sense in its original language.

Doubt yours is seizing as still it's too rich. What makes this simpler is focussing on one thing at a time. AC120 is correct. BE4 is correct. The main jet must be selected at WOT and max rpm. Increase the main jet until max throttle and max rpm in 2nd drops. Decrease main jet size until it leans out enough to rev to max rpm in 2nd (would guess 9000rpm) but still feels only just there. And stop. That's the main jet done.

Next start worrying about the pilot jet .

Bike revs out at about 9300-9500 with 138 jet fitted. What could be casuing the pilot jet issue? It's nice and quiet on the overrun with no popping etc but that's with any idle jet from 55-160 upward. Unless the difference is only slight with each jet increase.

The difference in the bike from a 145 to 138 is very noticeable. Much more responsive and powerful. But for some reason the bike hates 3/4 to WOT in 4th gear. Proper heats up. I dare not WOT in 4th for long in case of a seize.

That plug colour is from a WOT run in 2nd for 10 seconds with revs at 9000 ish. I am also adding 1% oil in the tank. Is the plug colour ok?

Thanks.

Here is a video of some 2nd and 3rd gear WOT runs. 2nd WOT revs up to around 8700 - 9300 depending on incline/decline. Temp does not get above 115C. 3rd gear revs up to about 8200 with temps around the same. I kept it WOT until the temp leveled out and increased no more than 1 or 2 degrees over a few seconds. The bike really warms up in 4th gear when loaded up. Is that normal? Temps are very low running WOT in 2nd and 3rd when compared to 4th.

Not sounding so rich now. Leave the main jet there but try it with a bigger pilot jet. Try 65/160 with 2.5 turns and do the WOT runs again.

That was with a 68/160 2.5 turns out. What effect will the pilot have in the WOT runs? I have my idle set at 1500 rpm. Is this within the idle range or am I in main jet territory? If so may have something to do with the idle not really responding to jet or mixture screw changes. Apologies if I am talking shite. I went for a good 80 mile ride today. Checked the spark plug after and it's totally different to other picture I posted. The insulator is more black/brown the whole way down. I didn't change any jetting so fuck knows what is going on there. At some points I was WOT and hammering it but mostly about 1/3 to 1/2 throttle. I suppose it's better than the plug having no colour at all.

On an SI carb the pilot has a big overlap. What you already did would have been the next test.
This is still the 24/24 carb without the vortex?
Bold move riding an unjetted 2 stroke 80miles. That's way more than pushing distance.
Tickover is 800rpm. Even if you don't like 800, it should still be capable of holding 800rpm until the fuel tank runs out.
Set the pilot at about 1000rpm and start with the mixture screw all the way out moving in.

I figured that the main jet is good and pilot is still rich. I kept a close eye on temps and it never rose above 160 and that was up a steep incline. When I do go from WOT to idle the temps drop. Also when going downhill in any gear with no throttle, the temps fall. There is no way the engine will idle at 800 rpm. Maybe 1000 but as soon as I engage clutch and select 1st, it will stall.

I will have a mess about with the idle tomorrow. I don't hold much hope for an idle that low.

So leave in the 68/160, mixture screw say 5 turns out, then turn it in and try for a tickover of 800 rpm or 1000?

If the engine is in good condition and jetted well, it will idle that low.
About 1000 rpm is good for setting up. With a rich main stack, it bleeds over the pilot if the revs get too high, as you already found out.
The jet that lifts the rpm at 2.5 turns is what you're looking for. On that BGM set it will be 60 or 62, most likely.
After you're done, set to 800rpm, rev high, let go and it will return to idle in a few seconds without popping or stalling.
The big pilot test though, is what happens at the 3000rpm transition under load.

Here are a couple of videos using the 160-60 pilot jet. No chance of it idling at 800 but I got as low as 1000 rpm and it was not happy. It's more happy idling between 1400 and 1500 rpm. If I put into gear at any lower rpm then after a few seconds it stalls.

What does it sound like when revving and coming back down to idle? The revs settle quickly with some popping at the end at around 2500 rpm and lower. Is this normal?

To be honest I can hear or feel any difference between the 58-160 and 68-160 pilot jet. The mixture screw was set at 2.5 turns out for these tests. When wound right in, the revs increase. With half a turn out they decrease but revs don't settle and there is a lot more popping. Wind it out to 2.5 and that's what happens in the videos.

Just to add, the engine was not fully warmed up. I did this about 30 mins after a ride out.

How much extra oil should I be putting in the tank? I am adding and extra 1% at the moment. 60ml for 6 litres. Each time I fill up it always seems to be 6 litres.

Sounds not bad. Slightly rich. Go down another size. Even better reduce the jet way down until it lean bogs when coming off tickover. Just so you know where dangerous is.

Oooo, you're getting there. I hope this story goes from wanting to set in on fire to loving it forever and riding it many miles into many sunsets.