Modern Vespa

I'm having this issue on my 150px with a bgm bigbox v1.0 a 24/24e and a new 160/55 160/BE3/100 jet set . I'm at 9300ft so that's why I downjet 9 sizes from stock. I tried the 108 first but it was boggy and farty af.

The spark was nice brown w/100 but I had a severe flooding situation after a brief engine stops, no matter how brief. Lots of kicks and WOT for a sweaty Saturday and a lot of smoke! I see signs of oil/air? leaks at the cylinder 'neck' where the two parts match, and at the exhaust stub. While jetting, I screwed the mix screw all the way in and the bike kept running with the 160/55. The fuel gauge feels kind of stiff too. I recently replaced the needle but nada.

I then switched back to the 120/40 that was previously installed but the plug looks unwell. I'm gonna do the switch back to the 160/55 today as I suspect there's another reason for the bike to keep going with the screw all the way in. Until I can fix the cylinder leaks, maybe I'll try a drilled air filter I have on the 200 to see what happens. Probably try a 105 main jet with that.

The bike had a slight hesitation when releasing throttle and then accelerating again. It was gone I think with the new idle jet.

I have some new shims that are for the v2-3 bgm (didn't try the beer can shim) that I'll fix with some copper high temp gasket paste. I think I only want to apply it on the exhaust side and let the spring (currently uninstalled) do the rest of the job. Is this a smart idea or I need to paste it on the cylinder stub too. Is this a smart idea if I eventually have to remove it? I've read a slight leak is fine there, and this version of the exhaust has no tightening screw or clamp.

If I may add, the hesitation was still there with the new be3 atomizer. It had an e3 before, so that's another sign the 120/40 wasn't ideal.

@pdxjim said in a 2014 post on the subject that if the engine keeps going it may be that the starter circuit is leaking or the idle speed screw is set too fast.

How can I check for the first suggestion and how do you guys think I should proceed?

Careful what you read! This is not true for your carb. The SI carb has a mixture screw. This statement is for air screw carbs.
With a mixture screw when completely shut there is no primary fuel at idle, just the bleed from the main stack. Enough to stay running, if the main stack is rich enough.
On your carb, with a mixture screw it is the opposite. It should cut out at idle when at about 4 turns out.

If your main jet is 100 and still brown plug, the pilot at 55/160 will also be too big. Try 48/140 or something similar that ends in /140 or /160 not /120 or /100.

Thanks man!

I didn't know about this difference. Getting jets is very hard where I live so I must know the precise one to get. A temp. A common solution is fitting copper wires inside the main jet, locked in the side holes, but the idle is too tight for any stable wire + no lock.

In the meantime I'll go with the 55/160 a bit after 1 turn out. I'll report after the cylinder button-up. Is an air drilled filter a smart idea?

What pilot jets do you have?

Greetings:

Tuning a 2-Stroke engine that has a leak somewhere is challenging, in my experience.

If oil's coming out, there's a pretty good chance that air's getting in. You might be able to compensate with jetting in its current state, but gaskets usually don't "heal themselves". Also, the leak severity changes with RPM and resonant vibration. Solve the leak problem and jetting will get a whole lot easier.

Wheelman, you make a lot of sense. It's been less than 5000km over 8 years since the first and last case splitting I did when I got the bike. I hope I don't have to go that far and only button the top end up, and cables and things that feel as the grease has dried.

Jack, I have a couple 55/160s that I bought for this and another 24/24 on a px200. That one doesn't hesitate but is a little boggy mid-throttle so I'll try an E3 atomizer that this 150 was using.

Besides that, this one was using a 120/40 but it's too lean. I'd drill it, but the lower hole seems very tricky to get right. Otherwise I was thinking on buying a couple 48/140s from the Mercato, and save these for the beach days haha.

EDIT: I was reading that when the muffler is not properly locked onto the cylinder stub, the cylinder tends to pick up more heat. My exhaust has been very loose & no spring installed all these years, so maybe it's good to seal that.

Will this product be a good alternative for makeshift gaskets @cylinder head as well as exhaust? DonI apply at both sides of the shim or only exhaust side?


Permatex ultra copper gasket maker

The top air hole of the pilot jet is easy to change the size of. The fuel hole is impossible to change and be accurate enough. Any pilot with a 48 or 50 fuel hole can be made to work on your scooter.

Exhaust stub leaking needs to be fixed. This copper sealer is not something I would use but sure it will work. Cylinder base needs sealer of any type that removes easily. Cylinder head needs to be flattened if leaking, no sealer.