Lightened flywheel , misfire

Hi I have been having trouble getting scooter to run properly with the HP4 lightened flywheel I bought from SIP.

Keep getting a misfire, tried it with the spacer and without , it runs better without the spacer but still misfires, put original flywheel back on and it runs fine.

All the timing is set correctly, the mechanic doing it has fitted lots of these before and never had this problem.

Fitting it to a PX200 disc model, with malossi 210 kit , malossi exhaust ,T5 4th gear, 60mm crank, malossi reed valve with 30mm delorto carb and reinforced clutch basket and springs.

Any idea what might be causing it to misfire with lightened flywheel on?


Thanks for that Hamer, will have a look at that option, emailed SIP they just said use spacer, already have it and no different , told them in my email I used spacer, seems once you have bought a product they don't want to know, not the first time I've had no joy from them.

Change to what though ?

try to change your stator and spark plug..[Y]

For the record , this is just my opinion but HP4's are an absolute nightmare for this very reason - some work well but another seemingly identical will give nothing but grief. The PK XL modified flywheel is better , but I have found the best compromise for a light flywheel is the PX Electricstart item with the starter ring removed - its over 1kg lighter than standard non e/s units and has no bad press.


Have you checked the timing?

Event though the statorplate is on correct positions, the HP4 flywheel makes it wrong...


Because the magnets in the flywheel is placed by a drunk sailer, you can not rely on that it is the same as original Piaggio parts...


So  check the ignition/timing with a strobe.


Probably that is the problem.

Be very careful that the fins do not come loose and screw up your crank etc.

yes I am afraid I have to agree aftersales advice and support is the one area that has dramatically deteorated at SiP in the past few years. I appreciate that the business has expanded and the guys are very busy but its a bona fide case of bigger not always being better. I have waited weeks for responses previously and then had vague or even irrelevent responses - usually the solution offered is just to spend more money at SiP, odd that ??


Oh for the good old days when I could e-mail Ralf direct and get a proper relevent response in 24 - 48 hours eh ?

Cheers Hamer, I think I will go with the PK flywheel.


Svint has an excellent point here, this is almost certainly why they are so inconsistent in how they work when used without strobing.