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Discussion Starter · #1 ·
My father in-law and I completely rebuilt my Yamaha 600 SX engine from bottom up. We compression checked after rebuilding and had 130 each cylinder. We vac checked the block.

About 1 week after the rebuild I installed the motor and ran about 5 miles on the lake (I only ran 5 miles cause the wind chill was about -35 that weekend). Then this weekend went on a trip. I had mixed a 50:1 ratio in the fuel tank and also had set the oil pump to factory specs.

When I got to the destination took out of the truck and started it up. My buddy noticed how much compression it had (hard to pull). It started on third pull. We let warm up for about 10 min and then started to ride. I made sure not to go over about 7000 rpm. about 10 miles into our trek I had to wait for my buddy. It wasn't sounding good at idle. I shut it down and looked at the plugs. They looked OK - a bit oily but understandable with running at factory specs and oil in fuel for breakin period. We then changed plugs and that didn't help still was only running on 1 cylinder. I pulled the new plugs and found the PTO side wasn't firing.

Next we checked for spark and had good spark on both sides. I then held my finger over the whole and had a tons of compression on the mag side but very little on the PTO side. I was almost sick. This is the same side that the ring caught the exhaust port at 3300 miles like so many other twin yamaha 600's.

This wasn't the end to my delightful weekend. We left the sled there at a road intersection off the side of trail out of the way and they took me back to the house. They came back a couple hours later and we went to go load the sled onto the trailer. They had just come by about an hour earlier and saw the sled sitting there. When we got there the sled was gone!!! We could see in the snow where a pickup had backed up onto the trail. We called the cops to report that it was stolen. He said they just called that sled in to the local service shop for pickup as an abadoned sled. The thing wasn't there 4 hours and they had it picked up - what a crock!! It took me $75 to get my broken down sled back.

Anyways wasn't a good first weekend. So where so I start - I figure pull the heads and find out why no compression on the cylinder I had re-nicasiled. I guess I don't really know what could have caused this. If you have heard of anything happening like this I would like to at least eliminate a bunch of items if I can. Anything would be appreciated.
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