Restoring a JD 60 and now she will not start. I never changed the working mechanics as far as the engine goes. Removed Carb, cleaned it up and did a basic Carb kit, set the needles to 2 rotations. Had the coil/distributor off only long enough to clean/paint. Put back on at same location (notched setting), has strong spark new plugs. Anyway it back fired twice, yes back though the carb. Now 6 months later and long cold winter in Minnesota, trying to get back starting it. Upon further investigation when I rotating the engine with starter, air flows in through carb but flows back out what I think is the next stroke. Even then does not seem to be a strong flow. Don"t know since I am only rotating the engine with the starter and it is not running speed. Any ideas? Replaced oil but was never left without. Tractor was never outside. Timing not changed as far mechanical goes. Again any ideas? Last note tractor was running good, did 2 acres with JD227 picker / JD50 sheller under full load.