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Take a can of starting fluid and spray it around the base gasket and head gasket. Spray the intake and the carb boot as well it might be dry cracked. [ while running] If the rpm goes up your sucking air and it will run poor.[ bad gasket !] Retorque the head , it may not be flat [ loss of compression]. Something is changing shape on you when it gets warm. Do a cold compression check then one when it is warm. There will be a differance but not real large unless the rings aren't sealing. I do snowmobile motors all winter long here in Michigan and have seen this with heads that are warped on old motors. If the head is warped it can be fixed at any auto machine shop. Just cut enough to get it flat , you don't want the squish band under .060 or race fuel will be required. To check the squish use a piece of plumbers solder and bend it like the letter"L" . Now put it in the spark plug hole[ hold on to it] accross the piston pin, not intake to exhaust! It must touch the cylinder wall. Turn the motor over by hand a couple of time while holding the solder. Remove it and mic. the end that was smached between the squish band and the head. This is the important # on something like this i wouldn't go under .070 so you can just run 87 octain fuel. Hope this helps, start with the basics. Jim www.jrracing@wowway.com
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