State of piston/cylinder
 

Hello,
My gy6 75cc scooter loosed about half of its power, and its max speed si around 70kmh.
Its also starting harder when its cold outside. After trying to change everthing besides the cylinder and piston i tooked those two off.
Do you thing they are bad?
Attachment 765
Attachment 766
Attachment 767
Attachment 768

And also exhaust valve is orange, do you know what could this be?

thank you for anwsers.

The valves need adjusting. A small GY6 has its valves gapped at .002 inch and the valves stretch a little requiring an adjustment at the rocker arms. Check the gaps when you reassemble it and you will see.

Hello, the thing is that i builded scooter more than year ago with old cylinder and new piston. It went unbelibevle for two weeks, than it losed power. I changed vario, belt, clutch, ignition, engine head, crankshaft, camshaft, oil pump, final drive grearing and all bearings.

It gained a little bit of power, but not enought. I ajdusted valve clearance few times in meanwhile.

Thanks for anwsers!

Your exhaust valve is orange, meaning it is hanging open and not sealing correctly, and that you are running your fuel mixture too lean.

Replace the head, valves, valve springs, rockers, cam, gap valves to .004" (inches) and try again with PROPERLY adjusted carburetor.

It's hard to tell from pictures but it looks as if your cyls are out of round & your wrist pins are worn. On a motorcycle , I would bore it over .010 & put in new pistons , wristpins , crosshatch the cyl bores but like I say-It's hard to tell from pictures. By the way , I've worked on many motorcycles but a scooter may be different!:hmm::shrug: Irish:scoot::nuts:

Hello,
I tooked cylinder and piston to professional, he straightened cylinder out and honed it out. He said that it should be good now, because compression was leaking between head and cylinder. I ajdusted valve gaps and i hope that i will be able to finish everything tommorow. I will try with old carburator. Thanks