occasional backfire

[bucannon]

okay so i finially got my bike running pretty decent and got to take it on a trail ride for the first time since i bought it. it runs well with the new mikuni carb with 25 idle jet and 100 main.

occasionaly it will backfire out the carb. i believe it may be a timing issue so im thinking valve adjustment. but it has only 800 miles on it. am i wrong on my assumption?


what else would cause a backfire. it has no pattern to when it happens either. could the CDI be going bad? is it adjustable?

[FastDoc]

I usually associate backfiring with an ignition issue. I also think if it's too rich it can backfire out the exhaust from unburned fuel igniting.

I've also heard a lean condition can cause backfiring (more like 'popping') on deceleration.

Where do you trail ride around Galveston? I didn't think there was a place on the island for that, and that area of Texas between Galveston and Houston I don't remember as being rural at all. It's always interesting to see were people live and ride.

Take a walk on The Strand for me. I've had some good memories in Galveston.

[Weldangrind]

I agree with Doc that backfiring can be caused by a lean condition, and it presents upon rapid closing of the throttle. I leaned out an engine so badly last year that it sounded like a gunshot. A fatter main and slow jet fixed it. Try a 110 main.

[Wild_Alaskan]

turn the fuel mixture screw out a half a turn. its located on the bottom of the carb towards the intake tract and takes a flat head to turn. a lean or too slow idle is the most common cause of coughing through the carb

[bucannon]

i forgot to mention its backfiring out of the carb and not the exhaust. but as i said before it happens only occasionally. it idles at about 2000 rpm maybe a little higher, for now anyway.

i will be doing more carb adjustments as i ride it more and can test and tune. but im nearly certain its time for the valves to be adjusted. i have referenced the tutorial on how to and know i will need to drop the motor down some due to my valve cover. but that shouldnt be too hard, any pictures of this being done on an engine with out the valve caps.




In Galveston i ride on pelican island on the levee. it is really good for this as the hogs make some nice trails and the big lifted trucks that get stuck back there make nice ruts to go through. also if you go off galveston and take the bolivar ferry there are some good areas.


as for the Strand just about every weekend at night i can be found out there haha.

[Azriel_Strife]

Assuming this is a 200cc zong vertical engine.

they are jetted too lean from the factory, i see you have a mikuni on it, good choice.

The 25 idle jet should be perfect unless you are up at high altitude, your idle should be around 1400rpm. If you can't achieve that idle through adjustment your slow jet isn't the right size or the carb is dirty.

Since it is backfiring through the carb, I'm one to agree with the others and say it;s lean in the idle circuit, how far out is your idle mixture screw? if you need it farther then 2 full turns from bottom, your jet is too small.

your main jet is also too small, unless you are at higher altitudes. Weld is running 25/110 on his machine with the same carb. but he is at sea level more or less.

[Weldangrind]

True, although the Zong reference might cause some confusion. While Zongshen does make vertical Honda clones, they're most widely known (around here, anyway) for being excellent clones of the Yamaha TW200 engine, minus the long countershaft.

That said, my Gio Beast has a vertical Honda clone, made by Zongshen.

[bucannon]

so do yall recomend i wait to adjust the valves? and just keep messing with the carb?

[Weldangrind]

Definitely take the time to adjust the valves. They're often way too tight from the factory, which is harmful.