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I bought a 1993 Blaster a couple months ago as a project. Aftermarket parts include:

Full Fmf Exhaust
K&N Air Filter
Boyesen Reeds
Reed Spacer
Tors Delete
Automatic Oiler Delete
Aftermarket Stator

240 Main Jet
Needle in Middle position
Air Screw 1.5 turns out
I am at 5200ft Elevation

It wasn’t running when I purchased it, so I began to tear into it. The first thing I found was a broken carbon fiber reed, so I ordered up a new set of Boysens. When I got the cylinder off I didn’t think it looked too bad inside, though I am no expert. I did find the broken reed piece. I took the motor off, turned it upside down and gently blew air into it to make sure there were no pieces of the reed valve left. I then measured the cylinder with telescoping gauges and a digital caliper, and these are the measurements I got:

Xt - 65.94mm
Xm - 65.89mm
Xb - 65.81mm

Yt - 65.99mm
Ym - 65.99mm
Yb - 65.97mm

I also ordered up a Pro X top end kit and gaskets. I put the engine back together with the new parts and a carb clean. I torqued all the bolts to the proper specs and even used the Motion Pro torque wrench extension for the hard to reach bottom bolts. It literally fired right up. I did a couple heat cycles on it, and then took it for a short ride. Idle to ⅓ throttle it seemed just fine. At more than ⅓ throttle it completely fell on its face. I immediately thought it was a jetting issue, (running a 240 main) but investigated further to find it only had 60psi compression. I used 2 different compression meters and came up with the same result. I was running 32:1 Premix.

So, I decided to tear back into the engine. Attached are some pictures of what I found. This is where I definitely need some help. I checked the ring gaps and discovered they were 0.63mm and 0.58mm (0.20-0.35 is spec). I also noticed that the base gasket was wet almost all the way through.

The first piston photo is the brand new piston, after being run for about 20 mins, which looks to me like it got too hot.


The second is the old piston, which didn’t have any of the black scorched look to it.


The next two show the vertical lines in the cylinder. These weren’t here before the rebuild.


The last picture is of what looks like a heat spot on the crank, right at TDC. The crank still seems to be fine. Absolutely no up and down, little side to side, and spins very smoothly


There also seemed to be quite a bit of unburned fuel in the bottom end. Any advice or thoughts would be greatly appreciated. I’m planning to get the cylinder bored and go with Wiseco this time (which I probably should have the first time).
 
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