This summer I was using my 9N ford tractor and it was running fine.I was plowing a garden spot when it just quit running and I couldn't get it running again. I took it and had the engine rebuild but that didn't help either. After I got the engine home and put back into the tractor and it ran rough and wouldn't stay running it would pop and snap and back fire. I took it apart and noticed that some of valves were sticking and the compression was 105 psi 90 110 and 90. So I took it apart to look at it and the cylinder walls wasn't honed that well. I took the pistons out and rehoned the cylinders to a nice crosshatch pattern. I took the valves out and cleaned and lapped the valves and put some new seals in. Checked the timing between the crank and cam. Bought a new distributor , carburator and plugs and wires. The timing is right and it's firing good. It still won't run without holding the chock out and it still won't run right.The compression checks between 120 and 125 psi on all cylinders. I thought the timing might be 180 out. So i cranked the engine over 180 degrees. It seem to run better but it was still back firing through the carb. Still getting the popping sound and still can't get it run right. I figured with the compression great and firing great it would at lease run right. But it doesen't. I am at wits end and help or sugestions.