Forum

[NicoV]

What could the following be due to:
- misfiring when riding downhill
- when slowing down before a roundabout, misfiring starts and often continues until the engine stops.
The misfiring/farting comes from the inlet port.
It can only be avoided by mainting a constant rpm, which probably has to be more than 2000 rpm.
When the engine has stopped, it is not difficult to start it again, that is, 2-3 kicks.
I have a Jan.1999 Bullet 500.

[papasmurf]

I suspect the inlet valve is slightly open when it should be fully shut. Check the inlet valve pushrod adjustment.

[vince]

Hi, it could be the brake light shorting, does it do it if you slow down without using the brakes? IE engine braking. Vince

[NicoV]

Vince, I don't use the brake there. It happens when braking with the engine.

[papasmurf]

If you have got hot gases coming back out of the inlet as in out through the carburetor basically you are riding a bomb.

[NicoV]

Papasmurf, there is no misfiring all of the time, and I haven't been blown to heaven yet But: when the engine is stopped, I see smoke coming out of the airfilter. Scary !

[Gwilly]

Check your points haven't closed up, clean and regap.

While your in there check auto advance hasn't broken a spring, recheck timing..

Check spark plug for lean running, looking pale whitish is bad.

Did you recheck mixture and jetting after you replaced silencer?? Hows the running in new piston going? Retorqued head?

[Alan R]

Hi Guys------I think our friend is saying that he is getting back-firing through the Inlet Port / Carb ??..but it only happens when he is using the engine for braking.....Smoke from air filter when engine stopped = inlet valve partially open --- nothing scary about that really...But all that seems to point to a tight inlet valve setting OR--- he has a partially burn inlet valve seat OR}---- a small deposit build-up on the inlet valve seat ?? ( Poor fuel---bad settings )...Hi GWILLY, how do you know he has changed his silencer then ?? Are you Psi-Kick or what LoL !!

[NicoV]

Hi Gwilly,
the spark plug is white/yellow pointing to a maybe too lean mixture ? I never touched the jetting of the Mikcarb vm28, but did put the pin of the slide at the richest position.
Piston and piston rings have been run in for 1700 km now, but I still take it easy with the Bullet. I did retorque the head twice. The silencer is the original long bottle, but one bought from our host because the previous one had a rattling part in it.
Yes, I have to check the ignition timing. That is a very long time ago.
Alan, I also suspect the inlet valve. That misfiring has always been present, but it has gotten much,much worse now.
In the worst case I will have to remove the cylinder head and check.