Cub Starts and Run for 20 seconds or so, then dies

[Tom CA Cub '49]

Hello folks, seems I'm back again looking for some help with my 1949 Farmall Cub tractor. I have had this tractor for about 25 years or so and it has always been a good starter and a reliable tractor. I use it primarly with a front-mounted scraper blade to keep the weeds from getting out of control in the back of our property. Recently, however, I have run into some problems. I can get the tractor to start, and to run for about 20 seconds or so, then it dies. My first thought was a gas problem, so I made sure the gas line was clear and, in the process, ended up replacing the sediment bowl assembly (I broke off the old one trying to remove it). I also replaced the spark plugs with a fresh set, replaced the carburetor, and also the gas cap (tall style, vented). Still have the same problem. So I've been searching the net for more information since I clearly have not identified and fixed the original problem. One thread I found suggested the problem is likely the distributor coil (which has never been replaced by me at least). But the coil on my tractor doesn't look like anything I've see online when searching for a replacement. Mine is rectangular in shape.

Any information you might be able to provide me on the problem I'm having with my tractor, or my distributor coil, would be greatly appreciated.

Thanks, Tom

[Bob McCarty]

Did you remove and clean the main jet in the carb? With the jet out you can check for constant gas flow. A bad coil usually stops a tractor running after it gets hot (20-30 min of running time).

[tst]

you do not have a distributor, you have a magneto, check condition and points gap, .013, coil is internal under the square cap

[Glen]

Hi,
The Cub has a magneto, like tst said above. The coil is different than a coil for a Battery Ignition unit, or cars used in the past.
Below is a listing for a new coil from TM Tractor Parts, at the bottom of the page. You can look at the pics, it is a specially shaped coil. I'm not saying you need a new one, the pics are so you can see what it is.
http://www.tmtractor.com/new/el/713fp.htm

You didn't say what carburetor you put on the Cub, new or used.
Some of the new replacement IH style carbs have problems that need fixing, the float height may need setting. Some of them need a small hole drilled inside them, that was not done when they were made. There have been pics of it on here before.

The main jet in the IH carburetor is the 6 sided brass colored thing like a bolt head, low on the side of the carb.
Below are pics of cleaning it. Use a small wire in the hole in the end of it, and then wash it with carburetor cleaner. Wear your safety goggles when using spray carburetor cleaner.
It should have a gasket on it, if the gasket is old, they sometimes don't seal if you try to reuse it.
TM Tractor Parts has a new gasket if you need it.
Tighten it gently, the jet can break if overtightened.
There is a small screen at the gas inlet to the carburetor, it may need cleaning. Be careful tightening everything on the carb, they are soft metal, and threads can strip if overtightened.
The 2nd pic below, from TM Tractor Parts, shows the screen.

[Eugene]

I can get the tractor to start, and to run for about 20 seconds or so, then it dies.

When started, how does the tractor run? Rough, surge, smooth, miss?

How long after the 20 second run time before you can restart the engine?

The engine start and 20 second run time has me puzzled. Carburetor float set to low and just a trickle of fuel into the carb will provide a very short run time.

Have you checked for spark at the plugs after the tractor dies? 3rd or 4th down the possible list is the magneto coil breaking down.

[Tom CA Cub '49]

Thank you all for this very helpful information. I plan to get to work on this today. The carburetor is a new one that I bought on ebay. I was hoping, with a new carburetor, it would solve the problem but it did not. The tractor runs smooth, no misses, for 20 seconds or so, then dies, and can be started right up again after that. When I replaced the sediment bowl assembly, I cleaned the gas tank out to the best of my ability but I'm thinking now there may have been some dirt, etc. that clogs up the main jet. I will clean that out first and see if that helps. Also the carburetor float set too low may be the culprit as well, so I will check that out as well. I'll let you all know how this works out and thanks again.

[Eugene]

Put a spark test light on one of the plug wires. Start engine, keeping an eye on the spark test light. If light goes out while the engine is still revolving - magneto.

[Don McCombs]

Read this about carbs from eBay…

CHINESE REPRO CARBURETORS FROM EBAY.pdf

(209.2 KiB) Downloaded 30 times

[Tom CA Cub '49]

Ok, here is a quick update. Pulled the carburetor, adjusted the float which was set too low, and also ensure main jet was clean (it is). Reinstalled carburetor but still no go. Also, when I use starter fluid, spraying it into the carburetor right after I start the tractor, I can keep the tractor going as long as I keep spraying. So that tells me I have a gasoline problem, but so far I have not identified the exact reason why the tractor will not keep running. The hunt continues ....

[Bob McCarty]

Did you open the carb and check for the hole in Don's post?

[k hutchins]

What type of fuel line are you running? All metal as it was originally or rubber with an inline filter?
There are several threads on here about rubber lines breaking down due to ethanol gas and then clogging the filters or the screens leading into the carb as Glen pointed out.
I would take apart your old carb, make sure everything in it is clean and adjusted properly, and reinstall it. Double check the choke valve. It actually sounds to me like it's either choking out due to lack of air, or dying due to lack of fuel.
When l've had magneto coils go bad, it would run for a half hour to an hour then die. Also you'd have to wait a half hour or more to restart it.

Good luck.

[Tom CA Cub '49]

Here is another update. Yes, I opened the carb and found, as Don pointed out, that the hole was not drilled out. So, I carefully drilled it out and that's all set. The gas line is copper and I have no inline filter. I know inline filters can be helpful but honestly I think they end up being more trouble than they are worth in the long run. I think you have it right when you say that "It actually sounds to me like it's either choking out due to lack of air, or dying due to lack of fuel." I think that's what's happening. Will let you know how this goes.

[Jim Becker]

Make sure you didn't cross the throttle and choke linkages.

[Tom CA Cub '49]

Gentlemen, I am happy to report my Farmall Cub tractor is up and running! There is no doubt I could not have got it back running without all of your invaluable help and advice. Once again, the Farmall Cub Forum has saved the day! Thank you all so very much. All the best, Tom

[Jim Becker]

Okay, what was the fix?