OK, back to this tractor....and the problems I have been handed.
Started with a carburetor rebuild. Couldn't adjust the float and eventually found the viton seal was missing from the last "rebuild." Ordered a kit, new float, rebuilt, (yes, Roger I had to buy a replacement main nozzle because it had been previously removed!) and then the engine had gas and spark...but did not ever fire more than once or twice over a 30 minute period of trying, checking, trying.
Eventually did a compression test (note the engine had been rebuilt but never started), got 20 lbs. NOT GOOD. So we tore it down a little further, pulled the head, checked the valves. Exhaust valve had 0.010" clearance and intake had about 0.005". Piston was standard and the bore was 3.312" according to my handy dial ind.
Now this is where I needed a little expertise from you guys, I watched the valves and what seemed very odd to me was this: during the compression stroke (both valves should be closed) I noticed the exhaust valve would open ever so slightly, then close again as the piston reached the top of the cylinder. The rest of the timing looked correct for the intake and exhaust strokes. Is that supposed to happen on these HH100s? I am new to the RF world so any advice is good advice.