HELP, 80cc cutting out at higher revs

[Scorpion1]

My bike used to go 35 on flat ground and now will only go 25, it reaches a point where it just holds back, like its cutting out. I just replaced the carb with an hp carb and no difference in the top end. It has alot more torque and smoother response at lower rpms though.

IT RAN FINE FOR MONTHS, then one day started this

It is getting plenty of fuel flow as i have changed the petcock out a while back.

Is it 4 stroking?

Do i need a new ignition coil?, its still stock

HELP!!!!

 

[Agreen]

Check:
-spark plug
-head gasket
-crank case gaskets (there are seals around the crankshaft too)

Understand:
-4 stroking is braa-aa-aa-aa-aap. Like a machine gun. That means it's too rich.
-if it's too lean, it will just hit a wall and slow down. Try putting the choke on partially and see how it reacts. If it gets better, you may need to re-jet.

 

[Scorpion1]

I wish i knew exactly what 4 stroking was. The bike just stops revving and makes a choking sputtering sound at exactly 25 mph, any less and it runs perfect. I will definately get an NGK plug next. Could it be my cheap stock ignition coil? Should i get a new one. Will a CDI coil work on my china girl?

Thanks!!

 

[crassius]

check head gasket leak - loosen muffler to check for clogging

 

[Scorpion1]

check head gasket leak - loosen muffler to check for clogging

Will do, thanks

 

[Scorpion1]

Rings were worn. Replaced them and all the gaskets. Now its up to a steady 40 mph on flat ground.