Everything ran fine, until I added new parts...

[Stanton]

If you do believe it's the carb, then there are several threads in the How To Forum by Lurker Carl on carbs. Located here:
http://farmallcub.com/phpBB2/viewforum.php?f=139

You might start with How to Check the Fuel Level in your Carburetor.

[Jim Becker]

Could you be 180 degrees out on the timing?

Not if it was running.

As long as you have not touched anything in the ignition system since it ran, nothing timing-wise can be horribly wrong.

Have you checked for vacuum leaks at carb or manifold? Is it even possible to, at this point, to flood it by over-choking?

[MikeEyre74]

Well, like I said, it ran a bit yesterday.. maybe fifteen minutes until I shut it down, and then couldn’t get it going again. I don’t think it would have run at all if it were out at 180..

[Rick Spivey]

If you had good enough fire and fuel to run it for fifteen minutes, then I don't suspect anything is systemically wrong. However, there can be small gremlins that drive you nuts until you find and correct them. How are you shutting it down? If with a switch, then could the switch be worn or shorting intermittently to cause the issue? If you are flooding it out, then tune-up or carburetor is suspected. And if shutting off the fuel, then maybe fuel flow or gas cap vent is an issue when starting back up. Since it can run for fifteen minutes with no issues, start looking for something intermittent, or that is caused by shutting it off.

[MikeEyre74]

OK, I have at least part of this figured out. Right now, I have two magnetos that both make spark and, when installed, both will run the tractor. Yesterday at least, both of them managed to get the tractor started by handcrank. Let me back up a minute and explain… Because some of this is still a little bit of a mystery to me.

I think I explained earlier in the post, I had a complete magneto from a complete 1948 tractor that I put on here and it ran fine. I ordered parts for another magneto that I was putting together before I got my hands on that parts tractor, so those are the pieces that I put in the “parts magneto”. I could not get the “parts magneto” to work at all, so I started swapping bits and pieces over from the 1948 magneto to try and figure out what the issue was. When all was said and done, I had the parts magneto that just would not function with all of the new pieces that I threw at it, and my 1948 magneto would not start off the handcrank, but would start if I bumped it with the starter which I normally do not use because I don’t have a battery for it. In this instance, I bumped it off one of our vehicles in the driveway.

Yesterday, I stopped at the parts store and bought a new condenser. I would have bought two, but they only had one on the shelf. When I got home from work, I dismantled everything and put all of the original parts from the 1948 magneto back together again the way it was when it worked, and I put all of the new parts back into the “parts magneto“ housing, including the new condenser. I could not get the 1948 magneto to start by hand crank initially, so I bumped it off the car again and it ran. Then I shut it off with the switch, and then I was able to get it fired back up by handcrank after that. That is a step in the right direction at least. Then, I took that magneto out and installed the “parts magneto“ that was now testing good on the bench (thank goodness! It seems to have been the condenser?) and installed that in the tractor, and that fired up right away off the handcrank.

To summarize, the 1948 magneto is back together and appears to work, although I do not understand why? Then, the “parts magneto“ is also functioning fine, with all of the new parts that I got from Brillman and my local shop. I can at least wrap my head around why the second one, the “parts magneto” works, but I do not understand why the other one does now, being very finicky on having all of its original components together.

Just to answer Ricks questions above, I shut the tractor off with the original switch, yes. The carburetor has had a recent tuneup, and I have been through it numerous times over the past weekend and all appears in order. It runs fine when it is running, it is just starting that is the problem. And lastly, I am using the gas cap that was sent to me under the warranty job, the very tall black gas cap, and it is only three or four weeks old. Interesting, I would have the gas cap on and then remove it entirely to check for vent issues. It does not seem to be the gas cap, because it runs fine with that on there.

[Stanton]

Glad you got it running again.

[coppersmythe]

my loboy was acting up somewhat in a very similar manner . ran fine , wouldnt start , start fine . then it would stop at random points in cutting the grass . sometimes it would fire right back up , sometimes not . after much fiddling and searching , a wire on the ammeter was slightly loose , just enough to qualify as a gremlin . coppersmythe..................ps: key word , slightly , at first the connection seemed tight enough ....................

[Waif]

You might have two female magneto's!

You stuck with it though and caught an agreeable moment or two....

[mozer71]

These such good tips and advise. I have to come back Rick Spivey's reply 6/22. He knows magnetos and how some lose the rotor magnetism. One has to think about spinning a magneto with no load and when it actually starts the engine. Almost immediately there are adjustments made to improve the engine running. That doesn't mean it is going to start that way.
Edit. I had missed the more recent posts. There is still something about "dwell" . I never thought dwell would influence timing but it does. The older vehicles had a knob or lever to move the distributor closer to zero TDC and after starting, was adjusted for running. Well everybody knows this but cam lobes wear too.

[Cubfriend]

Have you ever tried running the Cub with the wire disconnected from the mag. If you have a switch problem, that will isolate the switch from the mag. If you need to stop the engine a screwdriver (make sure screwdriver handle is insulated) can ground the body of the mag. to the terminal on the side of the mag. Your switch should only have one spade on it for a mag.

[MikeEyre74]

Yes. The switch is not the problem. We have run it both with that switch connected and disconnected. We did it quite a bit while we were trying to diagnose the issue as well as rebuilding the magneto to get spark initially. Right now, the tractor starts up easily by hand, with all of the parts assembled as I described a few posts ago. As far as I can tell the condenser was the issue in one of them, and the other? I just don’t know… It works, so I don’t want to jinx it, but I don’t understand why.