qt50 fresh top end verticle scoring

matt boda1nz /

any one have any idea as to why this would happen?

1987 qt50

boyesen reeds

77.5 main jet

k and n filter

stock exhaust

30:1 yamalube mix

fresh bore with new yamaha piston and rings .25 over. 200 miles on cylinder

could this be because the bore was too small? there are no other marks on the cylinder

i cant feel anything with my fingernail so it's not scored bad at all. excellent running and pulls hard.

is this a case of overheating or piston too small?

DSC_0750.jpg

Re: qt50 fresh top end verticle scoring

those engines spin backwards combined with the thick iron cylinder and the laid down orientation of the cylinder means the exhaust side of the cylinder/piston gets fucked up. Run as rich as you can and carve a little lip into the exhaust side cylinder skirt to pick up more oil out of the case. Look at a lot of pictures of modern cylinders to get what i mean.

Re: qt50 fresh top end verticle scoring

matt boda1nz /

excellent. thanks ryan. guess i will try to richen her up as much as possible. i never put the oil on the k and n.. maybe i will oil the filter and see if that may help keep it richer.

Re: qt50 fresh top end verticle scoring

off topic but what measurements in your K&N?

Re: qt50 fresh top end verticle scoring

matt boda1nz /

k&n rc-2540

Re: qt50 fresh top end verticle scoring

matt boda1nz /

fits nice and snug.

Re: qt50 fresh top end verticle scoring

matt boda1nz /

ok.. i think i have been a bit lean on my mixture.. that could be part of my problem. i'm pretty new to engines and fine tuning but i am slowly learning. i richened up the mixture and it pulls much better and feel more comfortable. plugs are nice and colored.. before they were pretty light. it seems to run much better. smokes just enough to know its a two stroke.. so i assume she's getting close to perfect.

had fun tearing down and rebuilding the engine this winter. bearings, seals, reeds.. wish i would have been a bit more on the rich side for break in.. but you live and you learn. still has plenty of life in her. runs real nice. its like a whole new experience..

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