Carb/fueling problems

[kymco_super_50]

Hi,

Happy New Year everyone   My scooter started cutting off after the fuel in the carburetor is spent. I took the carburetor off, took it apart and cleaned everything, then put it all back. Also with the air filter. The same problem; it runs fine (light brown spark plug color) until the fuel from carb runs out. What I noticed is that it has an automatic cock fuel valve, meaning that it needs vacuum from the carb in order to release fuel on the line. Could the cut off be caused by not enough vacuum created for the auto cock to release fuel? Thanks Chris.

Kymco Super9 50AC 2008

[MotoRandy123]

Sometimes a fuel tank vent gets pinched off and won't allow free flow of fuel. If the
bike runs it creates enough vacuum to operate the vacuum petcock. Try running with
the fuel tank cap open and see if it stays running...

[kymco_super_50]

Thanks MotoRandy123, i will give it a try; I did open the fuel tank cap whenever it stopped and also created vacuum in order to get it restarted. Let me go and check.

[kymco_super_50]

Update 2: I've just got back from dstairs and did more testing. It seems the fuel is coming into the carb just fine. I turned engine on and removed the fuel line at the carb; full flow. I should have tried this test before. Still the scooter will idle on stand for one hour, but as soon as I go and run it at 20-30 mph for about 2-3 mins, it cuts off, with or without lights on. If fuel supply is not a problem, what else can it be? I cleaned carb yesterday - jets, float, throttle valve. The only test showing a possible problem is with the auto bystarter. It shows 6.4 Ohms instead of recommended under 5 Ohm. Could the auto bystarter cause the engine to cut off after riding the scooter for 5 mins, but allow it to idle for one hour???  Or I'm misreading the digital multimeter (lowest Ohm setting is 200, and the bystarter shows 0.64, so I'm not sure if this is 0.6 Ohms or 6.4 Ohms)

[MotoRandy123]

  Well it would make sense that the choke would change something after it warms up
so maybe it won't run when unchoked?

  On 200 range 0.64 is 0.64 ohms a short if you will. I think you can remove the choke
 and power it and after a bit it will pull in or push out but if it wasn't working the bike
would act the same all the time...

  

[kymco_super_50]

Thanks MotoRandy123, I will next remove the choke and test it to see if it's working when powered. Meantime, I had another go riding it in the hood, and as I soon as I turned the corner off my street it died again. As a last resort I followed your suggestion and opened the fuel tank. I put it back and tried to start it; it worked again. Went for a half hour ride and worked fine - speeds of 40 mph - so I am now completely baffled. I@m hardly confident to go too far, so I still need to find what causes it to cut off and then to work normally. 

[MotoRandy123]

   Well according to the service manual #95005 in your picture is the vent tube but I
don't know how it works as it seems to attach one part of the tank to another...

[wordslinger]

...could be that your carb's float (in the bowl) is out of adjustment...

..refer to your service manual for correct adjusting methods...

[kymco_super_50]

Thanks for all your comments and suggestion. I still can't figure whether the problem is fueling or something else. It starts fine when cold, I wait for the engine to warm and choke to go off, then it accelerates fine but when I stop at a traffic light engine dies as if it ran out of petrol. I tried increasing the idle rpms but it doesn't seem to make any difference. What else I should check? It stays at idle speed for an hour in the garage, and it runs with 40-45 mph so could it be:
carburetor settings?
Spark plug/coil?
Air/air filter related?
Bystarter?
Reed valve?

[MotoRandy123]

Well generally stalling at throttle chop is lean for some reason. Try changing the idle jet?
Or look for an air leak into the intake (tear in diaphragm, cracked vacuum hose, etc.)

Some have had trouble running when the air box is removed, have you modified that at all?

[wordslinger]

..maybe trash in the idle jet...

[Peters]

...could be that your carb's float (in the bowl) is out of adjustment...

..refer to your service manual for correct adjusting methods...

Or the float is sticking. Vibration allows it to move but at idle it sticks. I don't know... Just a thought