150cc GY6 scooter lost top speed

[sc00ter]

Are you sure you have the throttle cable ran correctly, and the slide is opening fully when you twist the throttle wide open? I've seen throttle cables ran wrong before, usually not seated correctly. There is also a barrel adjuster to take out the slack under the throttle. The throttle should only have a tiny bit of slack at idle.

So make sure the slide is completely opening and there is no excess slack in the throttle. I'll keep thinking......

[Battercake]

Originally Posted by sc00ter

Are you sure you have the throttle cable ran correctly, and the slide is opening fully when you twist the throttle wide open? I've seen throttle cables ran wrong before, usually not seated correctly. There is also a barrel adjuster to take out the slack under the throttle. The throttle should only have a tiny bit of slack at idle.

So make sure the slide is completely opening and there is no excess slack in the throttle. I'll keep thinking......

Yep, it's opening all the way to the top stop, and it closes all the way to the idle stop screw. The stator idea is plausible. I've read about them a bit today, and although I'm not having any of the other symptoms of a stator going bad, it's still possible because the windings are independent.

As I approach 46, it just starts to feel like I'm starving for something. It feels like I'm hitting gentle waves on a lake in a boat. Up to that point, though, everything is smooth and runs like it should, as far as I can tell. But there's some constriction in something that won't let it go any faster.

[Battercake]

Decided to ride to work today. The first few miles it let me go as fast as 51 for a while, but eventually it reined me back in to about 48 for the rest of the ride. This afternoon (when it was up in the 90s) it started out with its usual maximum of 46, but within a few miles decided that 41 was gonna be my new best friend the whole rest of the way home. I checked the spark plug cap, but it was secure. I can definitely feel like it's maybe not completely misfiring, but definitely underfiring a lot up near wherever that ceiling is at the time, but still seems to run perfectly at lower speeds.

[sc00ter]

So you said you swapped carbs and the same thing is happening. I'm gonna rule out a carb issue.

You checked/replaced the fuel supply lines. I'm ruling out fuel issue.

You said the spark plug looks normal.

You said oil level is correct.

You went thru the variator and said all looks good. Belt looks good and I assume you checked the rear clutch assembly. I gonna rule out a transmission issue.

Verify the earth ground is attached before proceeding.

You need to test the stator and see if its supplying the needed juice. YouTube has some good how-to videos.

Also, check the CDI. Again, YouTube. They will sometimes fail with little or no warning.

Finally, check/test the coil. Same symptoms as above. YouTube is your friend.

Don't get discouraged at a electrical issue. I hate trouble shooting electrical but have learned a lot with YouTube videos. We have a Subaru Baja that my wife refuses to get rid of. It has 270,000ish miles. I've learned so much fixing it myself, both mechanical and the dreaded electrical stuff. Still hate messing with it but its not a daily driver so it can sit while I'm learning.