Modern Vespa

Okay guys, no one really came to my rescue on this one. As a matter of fact, there are quite a few threads on here pertaining to the backfire/baby farts on deceleration on the LX150, Fly 150 etc, but non had a conclusive answer. Well, I have it now! After farting around with the scoot I have a most definitive answer as to what is causing it. I stripped the bike down and looked long and hard at it. And then I focused in on the Secondary Air System. If you're not familiar with it, become familiar. This little valve system pumps fresh air into the combustion chamber as a means to "dilute" hydro carbons etc for Cali emissions. Well, I guarantee that not all valves are made equal. I had an 06 Fly 150 previously, and it never backfired on deceleration. My new one does like there is no tomorrow. I disconnected the SAS completely and plugged the hole coming up from the head, and VOILA, problem solved! No more farting, backfiring or anything. Purred like a kitty! You will have to re-adjust your air fuel mixture and idle, but after that, you should be good to go. I don't have a permanent way to plug it off yet, so it had to go back on.....and the backfiring started again. So, there you have it. Hopefully this will help someone else out there who is scratching their head wondering what to do!

I thought this thread was about Baby Fark McGeezaks. But well done nonetheless Steph okay.

The scoot runs much quieter w/o the SAS system, and little spunkier too. Actually still had some mild backfiring/baby farts, so I pulled the valve cover off today. I couldn't even get a feeler gauge under the intake valve, and the exhaust was tight too. Reset both clearances, and smooter still! Runs like a champ!

I have the same issue, where do I find a diagram of the secondary air line and cylinder port?
I would love to have the snap,crackle, farting cease.-Nick

pic of SAS taken from lx150 workshop manual sorry its a screen shot but i think manual is somewhere on forum

Just as an aside to all, this symptom can have other causes, such as when your rollers need replacement.

My SAS has been bypassed for sometime. The metal hose broke during a high-speed run. Made quite a noise. The little LX sounded like a Harley for a couple days.

The bypass has had no effect on performance. In fact, it may actually be better, though I can't definitively say that's why.

It is technically illegal to do this in CA though getting caught is very unlikely to happen.