Modern Vespa

hi all..thanks for adding me to modern vespa.com..ride a px200 with a 210 malossi kit, i have changed the exhaust to a sip road 2 from a pm tuning expansion pipe, kept the same 130 main jet ( as advised by sip ) and it ran fine for a couple of days..now when i kick the bike up its started backfiring loud for a minuet or two.. any suggestions would be greatly welcome..thanks in advance. Jack

Welcome to MV from Latina, central Italy; I state that many years ago I had a modified Pinasco PX 125.
Question: which air filter is fitted? Check that it is not loose on the manifold.

standard piaggio air filter Attila..and is not loose..are you thinking this could be an air issue my friend ??

That or a problem related to the ignition advance, so from a distance it is difficult to diagnose.
We try.

thanks...will check out when it stops raining

Welcome to MV, jolly jack. I see you're from my home town, I was born and raised in Saltaire before my parents moved me 'over the boarder' into Lancashire many years ago. Sorry I can't help you with your problem, I'm not too familiar with the older Vespas. See what replies you get from this post, but if you're still struggling, you can always try re-posting your request in the Not-So-Modern section.

Exhaust leaks will cause backfiring on any bike. Check your installation.

nice to meet you on here matey..non stop rain here for the last week & garage roof leaking..need a bit o' nice weather to start fiddling..thanks for info pal

thanks pokeyjoe..first fine day will do that mate

Pull the flywheel and look at your woodruff key. Could be slipping/wearing out.

Pull your spark plug and see if she's gapped properly.

thanks everybody for the input..found it to be the join from exhaust to cylinder stub ( as pokeyjoe suggested ) ..cleaned it with thinners,rubbed holts firegum on & problem solved