We bought the bike in Wyoming and immediately took it out for some light off-roading. I was dissapointed to see that it was burning oil and stuttered at high RPM. Burning oil has to be rings or valve stem seals so I bought the parts to replace both. I didn't plan on doing that job right away.

Unfortunately for me, right before our next off-road outing I couldn't get the bike the start. It had spark so the problem was either compression or fuel. I pulled off the carb and cleaned it but the bike still wouldn't start. My compression tester doesn't have a threaded end small enough for this bike so I couldn't measure compression. I decided to tear down the top end and install those new parts.

I installed a cheapo cylinder and piston kit. It came with a new cylinder, piston, rings, head gasket, base gasket, cam chain tensioner gasket, wrist pin, and valve stem seals. I nstalled all that stuff except the valve stem seals. Those I chucked in the garbage and used genuine yamaha seals.

The combustion chamber had a lot of carbon built up. I cleaned up the valves, intake manifold, and exhaust manifolds. The original cylinder actually looked pretty good so I flipped the head upside down, filled the chamber with gas, and waited to see if it leaked past the closed valves. It did leak past, though not too quickly. I didn't have time to get new valves and seats, so I opted to lightly lap the valves and seats. Too may be lapping suction tool was too big for valves this small. Bummer. So I did all the lapping by twisting the valve at the stem by hand. That was tedious and couldn't put much pressure on it. I think the intake valve and seat look great. The exhaust valve seat still looks a little rough.

The head on this bike is annoying. You need a slide hammer to get out the pins that hold the rocker arms in place. While waiting for my new slide hammer to arrive, I was doing more research on this bike. The carb is not well liked and it seems that the pilot juet can get clogged in just 2 weeks of not running. Even though I had already cleaned the carb in my ultrasonic cleaner, I cleaned it again. This time I actually removed the pilot jet which did appear to be blocked. It is hard to say for sure because that jet hole is the smallest I have ever seen. Ultimately I think the fix for the bike not starting was cleaning the carb and pilot jet a second time.

I put everythign back together, changed the oil, adjsuted the valve clearance, and gave it a kick. A few kicks later it was running, just in time for our trip the next day.

I am happy to report that the bike is running well. It might still be burning a tiny bit of oil, but nothing like before. You really have to look for the smoke. The bike still breaks up a higher RPM. It feels like it should keep pulling but it sputters. I think the carb is at fault. But for typical RPMs, it is running strong.

I also installed a tachometer and hour gauge so I start keeping more detailed maintenance schedules.

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Smll Med Lrg bike won't start	Smll Med Lrg	Smll Med Lrg hmm, where is that oil drain plug	Smll Med Lrg its on the side, you don't actually need to remove the skid plate
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Smll Med Lrg	Smll Med Lrg crusty old carb, the original Mikuni VM20SS	Smll Med Lrg	Smll Med Lrg what a strange choke
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Smll Med Lrg	Smll Med Lrg this thing is actually pretty heavy	Smll Med Lrg float was adjusted way too high, it was certainly overflowing fuel slowly	Smll Med Lrg
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Smll Med Lrg float level set properly	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg Reinstalled the carb and the bike still wouldn't start. Proceeded with top end rebuild
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Smll Med Lrg	Smll Med Lrg	Smll Med Lrg getting the head bolts out requires removing all but one engine mounting bolts	Smll Med Lrg
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Smll Med Lrg	Smll Med Lrg	Smll Med Lrg lots of carbon on head	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg	Smll Med Lrg original cylinder looks pretty good. I will hold on to this cylinder	Smll Med Lrg
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Smll Med Lrg new cheapo cylinder on the left	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
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Smll Med Lrg gasoline does slowly leak past valves. Would likely be drained in about 90 minutes	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
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Smll Med Lrg Removed carbon from head.	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg removing rocker arm requires slide hammering out a bushing	Smll Med Lrg	Smll Med Lrg The pilot jet that I believe was still clogged after the first cleaning	Smll Med Lrg still clogged in this photo, though even once clear the hole is microscopic
Smll Med Lrg new slide hammer required to get rocker arms out	Smll Med Lrg	Smll Med Lrg the camshaft is so cute	Smll Med Lrg
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Smll Med Lrg	Smll Med Lrg exhaust valve looks very dirty	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg original valve seal	Smll Med Lrg	Smll Med Lrg	Smll Med Lrg
Smll Med Lrg	Smll Med Lrg valves cleaned up, ready for lapping	Smll Med Lrg	Smll Med Lrg lightly lapped valves, intake looks great, exhaust is better but not great
Smll Med Lrg after lapping the exhaust valve still has some pitting	Smll Med Lrg removed original valve stem seals	Smll Med Lrg installed new genuine yamaha valve stem seals	Smll Med Lrg
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