Carb Issues... VIDEO INSIDE

[AustinConnell]

My Zong 250GS '06 is having issues idling. I believe it has something to do with the carb. I have rebuilt the carb and cleaned it all out, but for some reason the motor sputters at "idle" and has a near backfire sound when descending the rev.
I have a video on youtube showing the carb firing some vapor out. I'm assuming that it is fuel being built up inside, but I'm not too sure.
http://www.youtube.com/watch?feature=player_profilepage&v=AjvnjE_nEKY
Any diagnosis or help would be greatly appreciated.
I can provide more information upon request.

Thanks in advance everyone![/url]

[Weldangrind]

It sounds lean to me. BTW, expect it to be lean when you're not using the air filter.

Have you tried adjusting the air / fuel screw (otherwise known as the pilot screw)? Try turning it counter-clockwise in 1/4 turn increments to see if there is an improvement.

[katoranger]

I would say that you are running too lean. It could be that the main jet is partially clogged or just not big enough. Also running without the air filter will lean out the carb more. Does it run better with the filter on?

Will it idle with the choke partially on? If so then that would indicate a lean condition.

[AustinConnell]

thanks for replies you two,

It won't idle for more than five seconds with or without choke.

I have tried adjusting the fuel mix screw, but nothing changes. I know that the rpms were supposed to vary, but I believe the circuit is clogged. I will be taking it all apart tomorrow again. I plan to get it all dropped in an ultrasonic cleaner soon also to remove any deposits.
As for running lean, I'm certain of it. I have pulled the plug out and it is super white.
I only had the air box disconnected to demonstrate the popping and vapor. The symptoms are the same with it all connected.

Also, any ideas about what the vapor is?

Thanks

[Weldangrind]

It's just fuel and air. It might be exaggerated by an improper valve setting. Come to think of it, setting the valves is a good idea.

Back to the carb, it's the slow jet and pilot screw that are responsible for idle quality. What size slow jet do you have in there now?

[katoranger]

Isn't this the model to have valve trouble? Need Doc to fill us in on it.

[FastDoc]

Isn't this the model to have valve trouble? Need Doc to fill us in on it.

Sometimes problems that seem like a mixture issue are not...

It could be that the carb is not the issue.

This model is known to have issues with poor compression. I say check the valves and check the compression.

Other common issues with this model revolve around the ignition and weak spark.

[AustinConnell]

I'm not sure what size jet I have, but I'm sure that its the stock one.

How much of a task is it to check the valve and compression?

[Weldangrind]

Not really a big deal, but certainly you need to set the valves before checking compression. On my machines, there is a large screw that acts as a plug in the center of the left side engine cover, and there is a smaller version at the top of the same cover. Does yours look like that?

[AustinConnell]

It has a bolt that is onthe rear side. I'm assuming that's the one you're referring to.

Heres a Google image of the side
http://www.sportbikes.net/forums/attachments/new-rider-forums/124889d1180495490-zongshen-zongshen-gs250-11.jpg

[Weldangrind]

I'm talking about the two silver coloured screws in the side cover; the large one in the center and the small one at about the 11:00 position.

[Weldangrind]

Spud's tutorial will get you started: Sierra 200 Valve Adjustment Photos (http://chinariders.net/modules.php?name=Forums&file=viewtopic&t=6458)

[AustinConnell]

I see what you mean now. I might give this a shot today. thanks

[AustinConnell]

the issue turned out to be a clogged carb.
I used an ultrasonic cleaner and a wirebrush to clean out all of the circuits and it runs like a champ!

Thank you to all of you for your help!

[Weldangrind]

Glad to hear you got it running. Thanks for the follow up.