Go-Kart engine problems (Briggs and Stratton)

My neighbor gave me his old go-kart and I fixed it up. The engine is giving me problems, though. It is a typical 5HP Briggs engine. It had been rained on with no air filter so I tore it down and cleaned it out and put it back together with new gaskets. I think they might have run it bone dry of oil because there was no oil in the crankcase but the cylinder and rings looked ok to me. So did the valves. It turns over just fine. The carb was very cruddy and I soaked it in carb dip and put it back together with new gaskets and diaphram.
After I got it all back together I started it up and it ran decently for a few hours. But then it started to run worse and worse. I bought a new carb for it and installed it tonight but it obviously wasn't the problem. Even with the new carb and with fresh gas it will only run with the choke all the way on. The new carb doesn't have an idle adjustment screw so it seems like it can't be a fuel problem. What else could it be? The only thing left is spark and compression. It obviously has both of those because it runs and had plenty of power when it was running OK which indicates compression is probably OK. I made sure the gas cap isn't blocked.
Any ideas what I should check next? Or what I should recheck?
Thanks, Gary
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Gary H wrote:

Hi, Timing?
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I thought about timing but it has a magnet and coil so is it even possible for the timing to be off? I'll have to investigate.
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timing is set by the key in the flywheel/crankshaft.If the flywheel gets loose it can partially shear this key throwing off the timing. Check your compression. did you check the valve clearance when you had it down...proper valve seating has more to do with compression than rings on these engines.
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How do I check compression on a small engine? I have a compression gauge for cars. Will it work? I think the timing is fine.
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Gary H wrote:

If it fits in the spark plug hole...
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Problem solved. I didn't have the carb to engine gasket on right and it was leaking. It runs like a top now.
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PS The gas tank looks pretty rusty inside but it doesn't make the gas turn rusty looking.
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If it runs with the choke on, it must be not getting enough fuel. Have you checked for intake leaks, loose carb, etc. Crud in the tank could have plugged a carb jet.
Bob
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Have you checked the fual line?
Bob
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It doesn't have a fuel line. The carb sits on top of the tank. Its a brand new carb so it doesn't seem like it would be clogged. Come to think of it, it ran better with the old carb I took off.
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