1989 moto 4 350 OEM spec carb problem.

[Ted Craig]

  I know a lot of people say not to use anything but Oem. For the sake of the those who chose not to, or the OEM part cost more than the project, lets hold back negative comments. 

  I just purchased a carburetor that is supposed to be up to OEM specs. The company has a good reputation on eBay and Amazon. The Carb is supposed to be for this bike and jetted exactly. 

  This question should basically go under carb adjustment. I installed the new carb, the bike idles fine. On throttle it sputters half the time and the other half it will rev up fine. Does this sound like the needle is set at the wrong point? Does it sound like the main jet is the wrong size? Or is there another adjustment besides the air/fuel screw thats is 2 turns out? 

  Yes i could truck through old threads and possibly find the answer, but i thought it would be nice to have one tailored to new carb installs. 

[06kfx440]

Is there a backfire when it bogs out? What does the plug look like? What was done to the bike besides a new carb? Why did you buy a new carb?


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[MarkinAR]

Just have to check the plug. Could be rich or lean. Jets in Chinese carbs are sometimes the wrong size or not stamped at all so they are tough to tune. If you have the old carb use the old jets if you can. I've used chinese from zoom zoom and they're decent for a clone but still hard to fine tune. 

[Ted Craig]

The new carb was installed for two reasons, the old carb was an old style that had two throttle cables. Plus it wasn't working properly after i rebuilt it. Nothing has been done besides the carb and starter rebuild. It had sat over 3 years and ran fine when parked. The throttle cable broke on me so i was stuck with that. Made a new throttle cable for this new carb out of the old set up. The plug is brand spanking new and i even put the old one back in and it does the same thing. It does backfire back into the air-box sometimes when it sputters. If you goose it hard it wants to die. If you slowly rev it half the time it try's to die half it revs fine. The exhaust is not clogged and the air filter is new but not oiled. Idk if they required oil, but it is a foam filter. 

Yea it is a zoom zoom. It seems a tad rich or black, but its hard to tell since your supposed to check in mid power band. 

Im in the fine tuning but they said its stock jetting. Im waiting in them to give me more tuning instructions. 

Im probably going to switch main jets and go from there. 

[MarkinAR]

Use the old jets if they will interchange and I bet it'll perk up. Good reason to change carbs though, those dual throttle cables are way expensive. I've used a couple of zoom zoom carbs and they're not terrible. Last one i had the jets were stamped with a knock off K for kehin and weren't even close to spec. I used the old jets and it wasn't too bad. matter of fact I have a box full of clone jets bc i just can't make them run perfect. 

[Ted Craig]

lol an old 250r racer i knew used to drill his own sizes. They may be good for that but he used to race 250r 3wheelers then quads on alcohol. So that was all a headache on its own. Yea ill start with the main jet change and see what it does. The pilot jet should be fine since it idles great. It does backfire quit a bit on throttle. 

[Ted Craig]

Well after i did the swap it was close to the same. I did fractions of a turn on the air fuel screw and it quit backfiring....as of right now its a pass in my book. Main jet may have been a thousands off. Or a bur in it.

[MarkinAR]

Another odd issue I had with a clone carb once was the needle point. It had a blunt taper on it so it was slower to open fuel. I had to switch that from an old carb also that has a smooth needle design.