641 Workmaster occassionally missing/backfiring

Been several years since been on here because the tractor has been running great! So story is, last fall hosed it off and it started missing and backfiring. I dried out the distributor and ran fairly well but decided a good time to replace cap, condensor, and points. That went well except the replacement caps do not fit my tractor so I reused the one I had which looks good, minimal wear. After that, it would occasionally be hard to start, barely run, backfire, and sounded like it was missing a cylinder or two. Advancing the gas would kill it or backfire. Adjusted the cap and wires and haven't had problems since till yesterday.

Yesterdays symptoms were the same. Several times I monkeyed with the distributor and it would run fine and then start stumbling five minutes later. I've ruled out a fuel problem and have narrowed it to the key switch or condesor. I'd like to know if I'm headed in the right direction? Bare with me I am moving across the country next week and don't have access to testing tools. Just a screwdriver and wrench set. Just want to load it on the trailer under it's own power. I'd like an explanation of what the condensor does. Also I read where the distributor weights were not "throwing out". What would be the symptoms for that? thanks, Kyle

The condenser, when it is working properly, protects the points from excessive arcing so that they will hopefully last a while. The condenser can fail in two ways:

1. It can fail in an open state which results in not protecting the points from excessive arcing so the points will need frequent sanding or filing and they will wear to the point of needing to be replaced very quickly.

2. It can fail in a shorted condition, in which case the points would be bypassed completely and you would get no spark at all.

Both of those failure conditions can be intermittent or permanent, and if either one is intermittent, the symptoms could could also be worse when hot than cold.

The weights in the distributor are part of a centrifugally driven mechanical advance mechanism, which means that as the rpm's increase the weights pull out against the springs more and more and the farther out they get the more advance the timing gets. Not starting at all should not be related to the mechanical advance.

Has it been humid where your at?? If yes you cap could have some micro cracks in it that you can not see and water fills those cracks and causes odd problems. Now one way to test this but you will not like it is to grab the cap with the engine running. If doing that makes up jump then you have a cracked distributor cap and need to replace it. But when you replace it go to a good auto parts store or tractor dealer for one not TSC.
If the cap is not the problem check that you have a good blue/white spark that jumps a 1/4 inch gap or more at all plug wires.

I will have to say that it has been humid the last few days and the tractor does sit under my porch where it can be damp. Although, I did grab the cap while it was sputtering and was not shocked. Another thing is the generator light stays on even at higher revs(although weaker). When running right it would turn off after it idled up and I rev it up. It has been converted to 12volt and a 1 wire alternator.

Another thing is that it would falter when starting down an incline in the backyard? I wonder if the keyed ignition is acting up? It seems that the key does not line up in its usual position anymore. Some refer to this as a problem area. Will see, right now I haven't a chance to investigate spark.

Easy way to figure out if the switch is going bad by hot wiring it and run it. If it runs just fine hot wired then your problem is form the coil back. If you not sure how to hot wire it run a wire form the ignition side of the battery to the ignition side of the coil and try it out