Misfire at high revs

[CPH Lambretta]

I have a misfire/backfire at high revs on a new engine build I've just finished.
It starts easily and ticks over and no problem up to about 5500 revs then it begins to hold back like its running very rich. If I push it enough it back fires and white smoke comes out of the exhaust and carb.
Its a brand new BGM electronic ignition. Any ideas what I should check first before I start swapping/checking stuff?
Cheers Nick

[Starwave]

Hello

I had the same problem a while back, although can't recall any smoking. Eden, on this forum, suggested I change the pick up on the stator.
Apparently they can fail when warm and at higher revs but check out ok with a mulitimeter when in your garage, as mine did.
Anyway, due to a lack of time, I changed the complete stator plate and it was sorted. I have a new pick up to repair the old stator and will probably change the LV coil too so I have a refurbished spare. The LT coil's are so fragile! The wire is finer than a pube - no wonder they burn out. I've had a LV coil pack up on me since, just got me home from Weston but was really struggling.

cheers, Starwave

[CPH Lambretta]

Thanks for the answer, I was really hoping someone would say "its just the CDI, just change that and your sorted" but looks like I'm going to have to get the soldering iron out.
Cheers Nick

[arthur]

why dont you try a cdi first my mates scoot started misfiring at high revs on the c2c and it turned out to be the cdi..

[FREAK]

i have this every 500 miles or so on my rb22 its the plug cap and nipple on top of the spark plug that wears with the vibration have a look at yours might be simple as that

[Diablo]

Yes wise words.
Check the simple stuff first. Work from the plug backwards. Don't forget to isolate the headset ignition by taking the green wire from the loom out of the CDi.

[Steve S2]

Had a misfire when in the high revs last week. The cdi was only 4 weeks old, it run great until the high revs, I change the cdi for a old spare that I had and it then run great.

[alcoholic maniacs sc]

the low tension coil on idian and Italian stators fail. i do 10,000 miles a year on lammies and have then go regular, backfiring at higher revs and won't rev out like the main jets blocked. personally never had a cdi coil go. obviously check plug cap and plug first!!

[CPH Lambretta]

Thanks for all the replies, I'll try to check everything through at the weekend (starting at the easy end)