1989 Zuma, just rebuilt carb to OEM specs, turned air screw to factory setting, Removed gas cap in case not allowing air. Installed new spark plug. Scooter will fire and run for about 20 seconds then dies. Removed plug and found oil/gas mix on plug. wiped off and re-installed. Turned air screw from position half turn each direction and retried firing. Nothing. Original complaint with scooter was that it would loose power under acceleration i.e. going up hill. ATTENTION HAVE TO SELECT WRONG TYPE OF MOTORCYCLE TO GET TO POST. PLEASE NOTE THIS IS FOR A 1989 YAMAHA ZUMA RAZZ 50CC SCOOTER.

One of three things is occuring here. The IDLE SPEED SCREW (Phillips head) on the throttle plate is screwed in way too far. The L and H mixture screws are open way too much allowing the carb to use excessive fuel, even on startup. Those 2 screws may need adjusting. The metering lever in your carb is not adjusted flush with the carb body flange and is holding the gas needle open constantly. Check these things and post back.

the gas in the carb might bad might need to take apart and bolw out with some air and carb cleaner there are very tiny holes and the gas builds up a yellowish scale that can bolck the tiny holes i recomend a carb kit wich will give you new gaskets there are two adjustment screws on the carb if you take the spark plug out and it is wet you are getting to much gas and flooding it out try to turn the screws in if the screws have the little plastic caps on them remove them this will allow you to adjust the gas to the carb there is a hi and low the low is idle speed turn just enough so the chain dosent spin hi hold throttle down and adjust out till it will get wide open and sound clean no missing or struggling. i can post some photos of a chain saw taken apart to help you if you need it . please let me know if ther is any thing else i can do to help

try new gas, air filter.

the air fuel adjustment has little to do with what u have going on, but here is what u do, make sure the engine is at normal operating temp temperature (at least 185F) then verify idle speed is set to spec +or- 50 RPM, then turn the carb mixture adjusment screw in until the idle speed starts to drop off, then turn it back out until the idle speed increases to its highest point (u will need a hand held tachometer), when u have reached the highest idle turn the idle screw back in 1/4 trun, that is lean best idle.

The idle circuit is still plugged up or it would not be giving you this problem. Remove the carb and dis-assemble it then soak the parts in denatured alcohol for 30 minutes. Then use a spray carb cleaner to finish the job. Spray into all the little holes in the carb body. Especially spray into the air screw and throttle screw holes. Reassemble the carb and LIGHTLY seat the air and throttle screws then turn each of them one and one half turns outward. This is the factory setting. Before putting the slide back into the top of the carb, move the clip on the jet needle one notch lower on the needle. This will richen the low end fuel mix. Install a new spark plug and clean the air filter. Please rate my answer. Thanks.

the screw on the side of the carb controls air not fuel. dont know if this helps you but worked on mine

Half a turn is too much - 1/8th at a time.
Check for air leaks at manifold - both at crankcase and at carb ends.
Does it run (idle) on its own, or do you need to keep on the throttle?
Have you checked the other end (the exhaust!) as well? A blockage there will be as bad as a lack of fuel at the front end.
Make sure you have everything in place - air filter, etc. - as with those little 2T engines, they are far more susceptible to thigs like that than a bigger engine.

answered