Can't Get High Speed

[inthestx]

I have a 50cc scooter 08 and it idles fine and will take throttle right away no hesitation. When I reach a certain point the scooter bogs down and almost dies. Checked fuel flow good, vacum good, timing good, valves good, spark good but auto choke seems to be bad, circut open. When I remove the air flow tube from the carb I can achieve high speed or when I use my hand over the end of flow tube can achieve high speed. Will the auto choke prevent me from achieving high speed or is it something else I'm not looking at. Thank you for any help you can offer.

[scooter 49]

A look at your spark plug will tell you if you are running too lean or too rich.
A black sooty wet looking plug means too much gas =too rich.
A whitish looking spark plug end will indicate not enough gas and too much air =too lean.
Spark plug should have a cocoa or light brownish color on the end=perfect
You can try playing with your air screw on carb and see if that helps.
You can also adjust the clip on the throttle needle inside the carb up or down to achieve a leaner or richer condition.
The answer to your question about the choke causing the problem could be yes.
If the choke will not close, it means you are running too rich .
When you first start the scooter up does the engine rev higher and then slowly idle down?
If yes than your choke is okay.
If no then it is stuck open.

[inthestx]

Thank you for your reply.
The plug looks black and tried the air screw no change.
Did not try clip on the throttle needle.
It use to idle down when it was cold and warmed up but no longer.
But I had this problem before the auto choke started acting up.

[scooter 49]

Well either way your choke will need to be checked out or replaced.
Moving the throttle needle clip up will make carb run leaner
Moving it down will make it richer
In your case I would move it up a notch because your engine is running too rich.
If you do try the needle clip change I would check the color of your plug after awhile to make sure it looks okay.

[inthestx]

Thank You again for the reply.
I will replace the auto choke and try the throttle needle clip.

[inthestx]

Replaced auto choke tried throttle needle clip but still bogs down when you try to increase your speed.
Not sure what is causing the problem. Any advise would help.

[scooter 49]

One thing that was not mentioned is your air filter. Do you have one installed with a stock airbox and if so is it clean? Do you have any air leaks from the carb intake to the airbox? If all that checks out have you tried adjusting the air screw on the carburetor? Have you tried simply replacing your spark plug with a new one?

[inthestx]

Thank You again for your advice.

I have an air filter and it is clean with a stock box. I replaced all the vacum lines and clamps plus checked for air leaks and replaced o ring on intake. I replaced the plug when I replace the auto choke.When I take air filter box off and leave carb open with no air filter runs great. Could vacum canister cause this problem?

[scooter 49]

I would say the answer is yes. The carb is obviously not getting enough air. Did you check to see if their is that little restriction tube inside your air box? If you have one remove it.

[Marleyfan87]

I had these same issues with my 150cc scoot, and it turned out to be the top diaphragm in the carb. If you can't resolve the issue that may be a place to look.

[inthestx]

Yes I removed the restricter tube from the air box. I was thinking the diaphragm on the carb might be causing a problem and also thought the air canister might be causing a problem. My next move is to replace air canister then new diaphragm.

Thank You for all your help and advice with this problem.
Will report back on what happens.

[revgray5]

I had the same problem with my scooter and I wound up putting in a new carb because the diaphragm had a hole in it.  Tried to replace diapphragm, but company kept sending wrong one, so I just bought a new carb and it was like magic!

[Fox]

Small holes in diaphragms can be repaired with RTV silicone. Just have to clean the surface of the diaphragm really good being careful not to make the hole bigger and allow the silicone to cure for a full 24-36 hours before use because the rubber is exposed to fuel.