GY6 150cc backfire issue

[parbs]

Hello everyone,
i have a gy6 150cc scooter issue. I thought someone might be able to help.
The scooter starts and runs great for the first 15 minutes. It idles about 1500-1900rpm. Throttle and carb is responsive.
After it warns up, it begins to run rough and backfires. It will run seemingly okay a idle. However, i notice at low idle, the rpm reads about 6000. I know this is not accurate. After cooling down, 20 minutes later, it runs excellent again.
what have i done to resolve the issue?
1. change plug with new
2. tightened exhaust to ensure no leaks
3. investigated any vacuum leaks. none found
4. replace carburetor
5. tried changing cdi box, no luck
6. checked and replaced fuel filter
7. left open gas tank lid thinking vent hose may have been blocked, no luck
8. Replaced spark plug wire, no luck

any suggestions? many thanks

[LorenStump]

Have you checked the auto choke?

[rks]

Adjust your valve clearances.

[parbs]

yes, new replaced choke.
i read in other forms valve clearance. not sure on this

[neo71665]

https://www.buggydepot.com/tech-cent...ng-gy6-valves/

I set them both to 0.004

[Roscoe]

The carbs seem pretty simple and I've some luck cleaning and adjusting them but an 18 dollar carb ordered online fixed one of the scooters. I could never get that one that came on it to work properly.
When your scooter quits if you are quick enough on the draw check the fuel drain and see is fuel will drain out. That's to determine if fuel is for some reason not getting from the tank to refill the carburetor bowl as needed.

[parbs]

thank' for the feedback.
I check the fuel line, it drains with no issues.
I noticed at initial startup, the rpm is about 1200-1500, normal rev. After 10-15 minutes of running & when it runs very rough/backfire, the rpm at low idle registers 6000 rpm. Note, this is not the true rpm. It rev's at same idle as the initial cold start up. I'm beginning to think it is the coil pickup sensor/switch.
The tach runs of the coil pack/pickup. I don't think it could be the magno.

[parbs]

I wanted to post a conclusion so that if anyone else has a similar issue. It resolved the problem. if scooter has a tough time starting, and if it's not the typical carb, it turned out to be the magnetic pickup and mag. Replaced both that came together and fire up perfectly.
thanks

[BeachScoot]

Try unscrewing the air/fuel mix screw front left of carb 1/2 a turn at a time...If You Get Past 3 1/2 Turns Then Go Up To Next Size Pilot Jet. I think its running lean