JD A not firing all the time

And tours of the local factories are available. Harvester, Seeding and Davenport (construction) are good tours.

~The the looser the engine & the tighter the carb seals the worse it seems to be.

~On those old 2-cylinder Deere's the firing sequence is the problem....first the L/H cylinder fires using most of the little available fuel air mixture in the manifold, then a short 180° later the R/H cylinder fires using what if any is pulled in during that short 180° cycle, then a full 540° later the L/H cylinder fires again & during that 540° the manifold fills up again so it gets a full charge…. What happens is during a slow idle the carb throttle plate is almost completely closed so only enough gets through for one cylinder to fire properly. As the throttle is opened up & the engine is run under a load the carb is opened farther & enough gets through for both sides to fire correctly.

~That is what gives the older Deere’s that unique popping sound at lower throttle settings.

~On the later 2-cylinder Deere’s with the 2 barrel carb’s that idle problem of one weak cylinder is pretty well eliminated due to each side having it’s own carb bore…

If you can turn either screw all the way in and it keeps running you need to rebuild the carb. If you can turn either screw all the way out and remove it while it keeps running you also need to rebuild the carb. You should be seeing lots of black smoke in this last scenario and the engine should die if the passages in the carb are not gummed or blocked. In the first scenario engine should die with a little or a lot of backfiring allowed.

Of course, there can be other causes why one cylinder may be stronger such as valves or compression or the spark quality caused by bad caps or rotors or plugs or wires on one side. You can observe the spark on BOTH plugs and try things like wire and plug swaps etc. to isolate those sort of problems.

Good Luck n God Bless

John T Nordhoff jmn50@msn.com