Modern Vespa

Riding my 2008 S150 home today I started hearing a back fire sound and it sounded like a popping sound. I pulled over and gave it some revs while leaning down. It is definitely sounding a little rough.

Kept going and the sound started getting worse. I pulled over again and called the wife to bring some oil. I had noticed that it was leaking a bit of oil through probably because I used the same gasket as last time (should have replaced it I guess).

Kept going and the sound just got worse. It is popping and back fireing like crazy when you give it some throttle. When you let off it runs fine and when it is idleing it runs fine too.

Anyone have any ideas? What did I do wrong? What should I check?

Two times I have heard a backfire or pop. Both happened when decelerating or at idle down times. One time it was a loose spark plug wire that was the cause but this also caused it to idle rough and it would also quit without warning when idling or decelerating. The other time is was gas in the evap. Same case there, the idle was erratic too.

Just my personal experiences from last spring and summer. Definitely get it looked at, it will probably get worse whatever the cause.

If it's not the plug wire, next would check for exhaust loose at the head.

Thanks, it seems to idle ok so I am hesitant to think it is an idle adjustment problem although it does die on deceleration when coming to a complete stop so maybe it is an issue. But it has had that issue for a couple years and this sound just started yesterday.

I've had gas in the line before and it was a different sound altogether and it wouldn't start.

I am leaning towards the spark plug line and the exhaust connection along with some idle adjustment. I'll check tonight after work. Thanks for your help!

So I went to check the gasket on the exhaust and it turns out the nuts are totally loose. I wonder how that happened all of a sudden. Its a good thing I didn't lose them.

So I tightened them and it seems to be running fine.

Now I am just hoping that I didn't do any damage to the engine by sucking air into the engine from the exhaust. I'm not sure what could happen but it sure doesn't sound like a good idea.

BEN i'd check things more regularly if your roads are as bad as ours our these days. I had my side stand bolt fall off. When i get my new rear brake line put in i'm going to be checking all the bolts because i' getting hammered with all the bumps etc in the roads these days. I wouldn't worry as i don't think you did any damage, you noticed it right away.

Had the same problem on my LX150. Turned out it was a loose exhaust. They are hard to get at but check the bolts holding the exhaust to the engine. You can get to them by removing the cover below the front of your seat.