Modern Vespa

Ok so I have a new to me V100 sport that starts great, Idles great, pulls great for the first 7-10 min, then it bogs. Can this be an airleak? my past air leak experience on other scoots has been that the engine races until I would pull the choke-- this scoot just bogs. I drilled out the gas cap vent hole (past experience led me there) , but have done no other trouble shooting. Any suggestions from experience smallframe comrades to start crossing off my checklist would be appreciated.

V100 sport, Ducati CDI, 12 volt Canadian/US battery model with a 125 top end and a stock dinky exhaust(which I just cooked clean on the BBQ)

Could be a leak. Check where the manifold bolts to the cases. I had an annoying one there on a 100 sport.

If you don't already, get some semi liquid sealer (RTV/Permatex motoseal) and coat the intake and exhaust manifold gaskets (both sides). Good goop and torqued nuts will really help in the long run.

So a Sport 100 w/ a 125 top end on it. Stock 125 or aftermarket? Still 16 carb or hopefully upgraded to a 19 when the cylinder was done, or something else? I wonder if they upjetted when they upped the displacement a whole bunch? Do you have pictures you'd care to share yet? We constantly need fresh scoots to look at here . TIA

If you want a good pipe, I really like this one for $175.
http://www.scootermercato.com/Scooter-Parts/Simonini/SIM40308

If you do need to upjet, get a box of 10 for 12.59 so you can find the sweet spot.
http://jet200.com/catalog/product_info.php?products_id=432 or one of the other size ranges. I found a 74 way too small on a port matched 125 w/ a pipe.

Thanks for your replies. So, Manifold was tight and sealed to the case, Carb is a 19mm, the cylinder kit is an et3 cheap scooterworks top end that I just put on - but the bike did the same with the stock cylinder - it started well cold idled fine, then when warm it would bog and die unless i fidled with the choke. I thought I'd put a new top end on, button it all tight, burn out the junk in the dinky pipe, and ... it now does exactly the same .. so my next steps are (help me here) 1.new CDi? or, 2. fuel tap? but why only when warm? or, 3. pull the flywheel and see if there is a flyside leak ( the engine doesn't race but rather bogs- so ?? my past experience has only been a racing engine with a leak) -- got a better Idea? lay it on me!
Thanks for the tip on the jets and pipe.

What main jet are you running? Your 3 port Scooterworks top end is an LML Sensation piece and I put the same one on that orange scooter and then increased the main jet until it ran without starving and bogging. But if you expect to upgrade the pipe, upjet AFTER that, and don't ride it around underjetted..

Sounds like a bad ignition. Is the CDI new? On some bad ignitions, the bike will start but after some some time the heat from the motor makes the ignition go bad. If you're sure about no carb leaks and the jets and bowl is clean, change out the cdi and see what happens.

Good luck!

When I was struggling with this, I found that the bogging would clear up when I pulled the "choke". It's not a traditional choke that closes off the air so the motor sucks in a richer mix. It just opens another circuit to add extra gas to "prime" the motor and help you start it.

So if choking helps, might be a clue it wants more gas and your jet is too small. So I went up real big, then started coming down size by size until a slight bog, then back up two sizes and no bog and done. It's OK to be a bit rich - more power. Not OK to be too lean.

Forgot to ask. IF it winds up clean and fast, revs nicely when it's first started, check this first.

Yes it has wound up nicely and revs well untill about 5 mins then it bogs. (I tried to post a video from my phone , but this upload technology is a mystery to me)

Well finally got to test the scoot for about 45 min after switching the main jet from a 74 to an 82 -- Huge difference! Thanks for your help. no if I could only learn to post a picture or a video from my Iphone!! ....