Planet Minis

josect50

My ct bike has a 70cc chinese honda type engine which i upgrated it to 97cc changing piston, rod and cylinder. I have also ported myself the intake and exhaust and installed a thicker manifoild with bigger carb. But since i have done this, the bike burns oil, after riding 1 block or 2 the smoking starts(you almost cant see backwards) and if you turn it of for 30 seconds ans start it again the smoke stops and the bike works perfectly.
I have changed piston again, checked the cylinder head with pressure, changed the valve seals, and cheked for almost overythings condition, this engine has aproximatly 1500km, i warm it up always before using...
I discovered that if using with the minumum oil it does not consumes almost any oil.
Please help, could it be cylinder problem?

mexicanyella

Could your crankcase vent tube be blocked? Any chance your oil drainback passage from the head is blocked, causing oil to accumulate in the head and find its way down valve guides?

Where in the engine are you seeing evidence of carbon from the burning oil? If it's the exhaust valve stem and guide, you'd see deposits downstream of the exhaust valve. If it's the intake valve stem and guide, and vacuum is sucking oil in, you'd see deposits on the valvestem and in the combustion chamber. If it was rings you'd be able to tell by feel and/or a compression check, I'd think.