Zongshen 250cc

[Wags]

Received new bike 250cc Zongshen. Doesn't run to well any ideas. It idles good but when third 1/3 throttle opened it pops and back fires but if at full throttle it disappears and goes good till you back off again.Bike is new and has done it since new ridden only twice. Rang supplier and have done his recommendations to no joy. So far checked valve clearence, adjusted fuel mixtures in and out from original setting, checked plug, checked air box for oil and obstructions, tighted all manifold bolts, Drilled out fuel outlet in tank and changed fuel line to 1/4 hose to get better fuel flow. Still no joy?

[50s BRotherhood #1]

unlucky bro...hav u cleaned out ur carby??

[SYMTEC23]

sound like its leaning out on fuel,the carby may need rejetting.

[tubes380]

if its backfiring it means that the fuel isnt being burnt maybe its the electrics or too much fuel. does it run when your on full throttle

[Wags]

Yes once its past the mid range poping and back firing it tends to run OK on full throttle.

[stevrossV1.0]

I just got a new zongshen 250cc motor and ripped out my zongshen 200cc so it is a 250cc in a 200 body!
Anyways your problem is that you are running too rich because of your main jet needle, it is too high in the main jet letting through too much fuel to air!
You need to go to a higher notch on the u clip so that the needle sits deeper in the main jet! Test and if its still a little rich then go up one more but not too much you dont want it too lean then it will overheat and mabee detonate!! Hope that helps!

[kwikaz]

could it be that the main jet is too big?? maybe a 102.5 would be the G.O.

[bennos1983]

what size jet do you have in it now? what brand of carbi and how big?

[ripsnort]

Seeing that the bike was new why not return it to dealer under usaul 12mnth 10000km Warranty and let them sort it out. You will void warranty by stuffing around with it.

[Ingleburn]

since this thread is over a year old the warranty would be up by now
10000KM/12 months what a crack up. If only there was such a thing. Wonder how many sellers would be still in business. Not many I suspect.