Hitchcocks Forum

My 2005 Bullet has developed a misfire/backfire through the carb when starting from cold. She fires and starts OK so long as I follow the starting procedure to the letter, otherwise she'll flood and wet the plug. Once running I have to be very nifty with the throttle in order to keep her going, the engine misfires/backfires through the carb,and will only continue to run through the most intuitive twistgrippery.
It's if the mixture is too lean, despite my using the enrichment lever. Once the engine is warm,perhaps two or three minutes, and I've returned the enrichment lever to it's normal position she runs perfectly and starts first prod every time.
I've stripped and cleaned the Mikarb (twice),checked,cleaned and gapped points and plug and checked wiring from coil, all to no avail. The enrichment circuit seems to be OK, as the engine dies instantly if engaged when warm. It feels like carb problem but experience tells me it's more likely something to do with the electrickery. I'm tempted to fit an electronic ignition system. All help most welcomely accepted.

After consideration, perhaps "backfire"through the carb is a bit dramatic.I should really have described it as spitting back. Humble apologies.

Mmmmm.....many Bullets will run with the enrichment lever on even when warm so perhaps it's too rich? Have you tried starting without the "choke"?

Yep, had the same thought myself. The bike is kept in a garage, and even starting at midday in summer requires choke. I've tried knocking the choke off as soon as she fires up but she just dies, as though out of fuel.

Almost certain its the pilot circuit, your having to open the throttle slide to provide enough air movement through the bore..

Remove the carb again and use wire on the pilot airways, small hole at the back and more important hole at the front just in front of the slide..

Unscrew the pilot/air adjuster well out and blast carb cleaner through the orifice intake and make sure it sprays from the front..

If your sure the float height is correct then set pilot screw to 1-1/2 turns out from fully in, should be a good starting point..

Unscrewing increases the air supply so if your going more than say 2-1/4 turns out then your pilot jet is too big and is too rich..

When warm the bike should run on throttle with the enrichment on, not well obviously, will fart about and eight stroke but should not cut out..

It is spitting back through the carb. The fault has developed, the carb has been washed, points correctly gapped. Too rich a mixture can produce carb spitting as can over advanced ignition at low revs. I'm wondering if the auto advance unit has a problem such as lost a spring or sticky operation? Just my 2d

Thanks lads, I'll have another go at the carb this afternoon. I was reluctant to use wire to clean through orifices, but if I must.....
I think auto advance is OK, as once running everything is fine. I'll report back later, apres lawn-mowing.

I think some people advise not using wire on fine brass jets but if it was that easy to ream out a jet to larger size then i've wasted pounds on precision drill bits over the years..

Don't worry as its only air supply and delivery holes which are adjustable via the screw, not metered as a jet is..

I reckon its that effinol stuff along with other chemicals which jellifies and blocks the small drillings if left for a few days to evaporate..

Gwilly/Beezabryan, carb cleaned as per your suggestion, (I used a single strand from telephone wire). Small holes around the outside if the pilot jet were blackened,presumably at least partially blocked. All back together again and completely refusing to fire at all, finally backfiring like a gun shot through the exhaust! Pumped things through with open throttle and ignition off/valve lifted ready to try again, this time without choke. Fired and ran second kick! Tried her with choke, as she wasn't running very smoothly, which she didn't like at all, so kept her running on the throttle. Went for a short ride and everything as it should be. Tried giving her choke with engine warm and running and she just ran lumpy. Looks like problem solved. Thanks a million chaps.