Help please- XT500 running rough
I have had a '78 XT500 stripped down mostly to a TT which has been loads of fun. I recently got my hands on an all original '77 XT500 from the original owner with ~10k miles on the clock. I got it with the carb jelled and the tank rusty but apart from that looking fine. Now that I have cleaned out the carb and hooked up my other tank for a temporary setup, I have not been able to get it running well. Fiddling with the carb, I can get the engine to either race at idle or smoke a lot and not really just get it running smooth. The spark was good with a new plug, the air filter was a brand new Uni and the fuel was fresh and stabilized. I then checked the compression on it and found out that it only had ~80 psi. I did not test compression immediately because it felt fine with the kick to me but I have not played with any other XTs than my two. I then did a leakdown test and was not able to find any leaks anywhere. I can hear the air rushing through the tube and into the cylinder, but cannot find out where it goes so fast. The exhaust is quiete, as is the carb, so it is not the valves. I sprayed soap water all around the cylinder and the gaskets seem fine. The crankcase vent did pressurize slightly if I held my finger over it for a while, but I thought this was normal cylinder blow-by. At this point I am just at the end of my rope and looking at taking the whole thing out of the frame and rebuilding it but it seems like such a waste for an engine with so few miles. The PO says it ran fine before it sat and I trust him. Any ideas or things to test for before I just tear it down? Any help would be appreciated. Also, if this post looks familiar, I posted over in the vintage section of thumpertalk... only getting a response to check this place out. So here I am to check out this forum. Thanks in advance.