top end hesitation

[oldcrow]

hello all, I have a gy6 150 long case, the engine is stock other than the cdi .. from 0 to 45 the motor runs strong, but at 50 to 65 the engine has a hesitation almost as if it is having pre- detonation problems ...I am at a lost with this one..please help.  thanks

[Rebel]

What have you done on this problem.

I would look in the air/fuel system. If it is starving out you might go up a size in the jet. Look for any kind of air leak first, some people have had to pull the air intake plastics off and go to a free flowing after market filter.

[oldcrow]

re-jetting might be the fix. I've tried the air fuel mixture it helped some but at the top end it still hesitates. going to try a hotter plug

[Rebel]

If it is starving out for fuel, I don't think a hotter plug will help. People put hotter plugs in sometimes to keep them from getting carbon fowled. Are you having a carbon build up on the plug?

[laemjohnson]

I have an 07 vintage with the gy6 engine and at 40-45 it acts as though it is starving for fuel and can't get any more power out of it.any help would be grateful since I am new to the bike thing. Was handed to me in this condition. But it has a new fuel pump and filter and all vacuum lines are good.

[Rebel]

Laemjohnson,

Welcome, you may have the same issue being discussed in this thread. Is your sooter also a 150cc?

[laemjohnson]

Yes it is. Have gone through the carb a few times already. I normally work on cars so I have idea of what to look for. Yet this seem to get the better of me I guess.

[Rebel]

Double check your valve adjustment then. Valve adjustment a common problem on a GY6 motor. Is the CDI the stock unit? some have a rev limiter.

[laemjohnson]

The cdi is the stock one. I adjusted the a/f mix and problem only got worse. Right now it is as lean as it can go and went back to before. I don't know of a rev limiter on this. What would it look like? Thinking of getting new jets for it to, the main is the stock 108 and I am at sea level in Washington could that cause this problem? Still going to check the valves though.

[Rebel]

The rev limiter is built into the cdi, not common in a 150 but at one time very common in a 49/50cc, the part interchanges. If it has. Pink wire you might disconnect it.

Intake is not blocked is it, if it sat for a long time rodents will build nests in the air filter.

[laemjohnson]

No pink wire on the cdi just has 4 wires and the intake is clear it had been running just the problem was getting worse over time. Thinking about blocking off vac lines and going with electronic fuel pump just to eliminate one problem. Could be cheap vac pump (jimbo brand). Your thoughts?

[jmkjr72]

Ele furl pumaps you may not have the juice to run
Get yourself a test bottle set up
It is just a gravity fed bottle that you will hook to n the carb and leave higher then the carb and go for a test run if the problem stays it's not the fuel pumy
Goes away you k n ow the problew and you can get a nice mukuni vacuum pumy

Also don't some of the 150 have some sort of booster thing on the carb to bypass I know yamaha had a deal on the vinos

[jmkjr72]

But the basics are done right
Valves adjusted
Fresh spark plug
Clear intake and exhaust I have seen a ton of mud dauber block exhausts
Belt is I n good shape as well as the rear sheave that 40 to 45 cold be a contract spring issue or if the pin path in the rear sheave is nto a nice linear line it can give y
Issues in tha t range

[Rebel]

If the gas tank is above the motor you probably have a vacuum petcock not fuelpump. The ones with pumps have the tanks in the floor board. You can rig up a simple manual petcock and dump the vacuum one if you want.

[laemjohnson]

The gas tank is in the floor board. I just did the valves. one was off. Haven't got time to ride and find out. It does have a auto choke on it. Thanks for all the help.