150cc GY6 scooter lost top speed

[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.