First thing to do is consult with the aftermarket manufacturer of the ignition. It sounds like that is the problem. It sounds to me like the ignition is not advancing, which would account for for all the symptoms you describe. Perhaps it is not the correct model of ignition for the application. Remaining retarded would cause loss of power, thus not burning all the fuel, which would darken the exhaust, and cause delayed acceleration, from indications, it could cause misfire when shut down, but it surprises me it backfires when started, that would indicate an advanced condition, or a weak valve spring, possibly moisture in the ignition. I feel when you find your problem, it will be in the ignition, that is where I would look. Since you had the carburetor apart unsuccessfully, I would get a kit from an Agco dealer as Frank said, and make sure to rebuild it correctly, it is cheap and couldn&#039;t hurt it. It would not be unusual to have parts that don&#039;t fit, and parts left over from an aftermarket carburetor kit, such as NAPA, often these kits fit several applications, and are packaged with sufficient parts for all applications they fit. Another thing I would check, a really dumb question, but could your distributor be 180 out? Check that the #1 cylinder is at the top of the compression stroke, with both valves closed, when the rotor in the distributor is pointing towards the #1 sparkplug wire.

[Edited on 24-10-2003 by Andy]

[Edited on 24-10-2003 by Andy]