Modern Vespa

I've had a problem with my Vespa stalling out,sputtering and jerking when I reach speeds of above 90 Km/hr to the point of having to pull over.When I brake it seems it wants to keep going forward then comes to a stop.I've changed the fuel tap and vacuum line,removed the SAS and blocked it off and removed the Evap,changed the plug,adjusted the mixture,cleaned the carb and put in a 38 jet.It doesn't happen all the time but it's a nuisance.The modifications I've made are a PM Tuning exhaust,a new belt and Dr.Pulleys a weight higher than stock,nothing drastic.I really would like any imput you guys might have.Thanks.

Explain this. Not normal. Might be key.

If the surging ahead were unrelated, which it may well be, I would say to check the tank venting (cap?)

I have a fuel injected model, I too also have a pm tuning exhaust. I can confirm I also experience the bikes willingness to keep going whilst coming to a stop. The revs seem to hold and the clutch stays engaged untill a near stop. This usually stops after half or mile or so though after start up. Probably when the fuel injection leans up the mixture slightly as the engine heats up. But yeah, the pm tuning pipe does seem to hold the revs and is probably un related to your main issue.

thanks for that,the main issue is a big problem,sputtering and coughing at high speed to the point of having to pull over..I honestly don't know causes this problem.

How many miles do you have on it? Also, and this is a shot in the dark, have you ever changed out the fuel and vacuum lines? I have a '07 and i've done mine twice (every 4yrs). You can't tell their bad by looking at them either. I would think if the fuel line isn't good at higher speeds it's not going to get enough gas. Anyway you should change them out before they strand you. Hopefully it will fix your symptoms. If not then we'll try something else. They should be done anyway. What color did you get? I have the Daring Plum. '07 had some cool colors. Have almost 39,000 miles on mine.

My Vespa has 10,600 Km and is Nero Graphite with a navy blue seat with some decals and front and rear racks and a short windshield,looks awesome..i took great care of it.I'll post a picture soon I changed the fuel line with no improvement.When it starts to stall out at 50 Kph I let off the throttle and it backfires a bit.It's starting to really act up now where it might leave me stranded and living in Canada stranded means the wolves will eat me so any help is appreciated.

NC Rick..what would I look for with the cap?Should I vent it with a few small holes?

You have a carb model, not fuel injected. Did you change the vacuum line when you replaced the fuel line? The backfiring is from unburned fuel in hot header/exhaust, in other words, you are running too rich and you carb probably needs to be looked at.

I suspected a carb problem,thanks for your advice Tierney

Did the symptoms start when you changed out the exhaust and jets? I'd put it back to stock and see what it does.

gotta be a solution other than putting it back to stock.

I think Judy means to put it back to stock to see if the issues vanishes and if so, you'd know where the problem lies and what to do. In this case, re jet.

Oh ok,thank you all,I'll try that.

Sorry (thanks Knights), yes that what i mean. That's the only way you'll know if it's something you did or if it's bad parts. Have you done other mods to it? If you have you don't have to change those because the bike was running well except for after the new jets and exhaust. Tell us what you find if you can. Good luck and finger crossed for you

I changed the belt and variator weights including the exhaust and jet.Thats all.I changed the jet back to stock as Judy suggested but it still acts up while doing a constant speed of 80 KPH.It will run fine for a while and start sputtering.I am wondering if it is the coil?Can the coil cause trouble like this?

I don't see why it couldn't. I've replaced mine years ago. I'll defer to people who are more mechanically inclined than i am but you might be on to something. I can't remember why we changed out mine. Altho it was a tad longer than the one we took out. We didn't make sure it didn't move. Hit the muffler and melted it.