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My S150 2009 has been running like a dream for years.. recently my Sito Plus exhaust rusted out and I replaced it with another slightly used one.. However, I noticed recently with the old and new exhaust that the bike is having trouble going into neutral when coasting down. It like to stay in gear till im almost stopped, sometimes almost cuts the engine off, and backfires huge flames out the rear.

It feels like its still under vaccum till it finally goes to neutral and idles at a stop. Im wondering if my new used exhaust is the culprit and also clogged up, or if this could be a vaccum line issue? Also now under power, I feel like its struggling to breath when full power. I have checked for a clean intake, clean filter, new clutch spring (small and big), etc.. its either a clogged vaccum line or the exhaust is clogged and isnt alowing backpressure to let the engine breath..

any thoughts or ideas?

btw, my bike is fully modified, 190cc kit, bigger jet, soho cam, etc... not that it should make a diff.. also my evap system is gone for years now.. but again she has been purring like a kitten since the exhaust issues began..
@theknights20 avatar
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Vespa s 125 ie 4t
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Vespa s 125 ie 4t
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Your s the injected leader like mine?

Mine does this with the pm pipe if I don't allow it to warm up for a min or two. The first few times you come to a stop it feels like its trying to keep going untill you come to a stop and then like yours the clutch disengages and the revs drop to idle. Does induce a pop sometimes too.

Its odd and I have bo idea what's causing it. I'm also running sluggishly too but miles better since I replaced the o2 sensor(mine had a hole in it). I was assuming my engine was still clearing its throat from running to rich. After reading this, I think its time to inspect a few lines again.

It is an odd one, maybe we can work this out.

Edit: "bigger jet" missed that the first time! So its the carb model.

Don't think its a kit issue, I'm running stock with just the pm pipe.

Have you checked this new exhaust is sealed actually? Blowing can cause these symptoms.
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2007 LX150 Daring Plum Leonardo Da Vespa
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2007 LX150 Daring Plum Leonardo Da Vespa
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Don't think the '09 is fuel injected. That said i haven't a clue why there would be flames. However there's a small gasket up in there that you can't see from the OEM exhaust. Don't know if that would cause flames when you swapped out the exhaust and left it in. Good luck
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2018 GTS Super
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2018 GTS Super
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UTC quote
rambino wrote:
noticed recently with the old and new exhaust
Same symptoms before and after exhaust change should eliminate new exhaust.
Quote:
the bike is having trouble going into neutral when coasting down. It like to stay in gear till I'm almost stopped
Clutch issue? Should be disengaging at approx. 10 mph.
Quote:
sometimes almost cuts the engine off, and backfires huge flames out the rear.
??? No clue on this one.
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