Cub backfiring

1948 cub was sitting idling for about 10 minutes. Got on it to move it and it seemed to load up with fuel and then died. It had some black smoke when it died. Now it will only backfire and won’t run. Won’t start with crank or battery. Plug wires are secure, drained fuel to make sure it wasn’t flooded. Cap and rotor appear to be nearly new and plug wires are new. I’m stumped.

Does this tractor still have the mag or has it been converted to a distributor?

It is still 6 volt positive ground with the mag.

If I have posted this once I have posted it a hundred times. TROUBLE shoot.
#1 check that you have a good blue white spark at the center wire of the distributor if it has a distributor and at all 4 plug wires that will jump a 1/4 inch gap or more.
#2 pull the carb drain plug and make sure you have a good steady flow of gas that will fill a pint jar in less then 3 minutes.
#3 when was the last time you serviced the air cleaner and dumped the mud and water out of it and filled it with fresh oil
Post back what you find if you need more info/help

Cleaned the air cleaner three weeks ago with gas and put in fresh oil. At that time verified it can fill a mason jar in under a minute out of the bowl of the carb. We have ran the tractor almost daily for about half an hour since with no problems. I didn’t re-verify those things today but I will.

i always thought they if an engine back fired, it was out of time.

especially since yours will not start. jumped time, maybe something slipped.

(quoted from post at 18:12:42 07/29/18) 1948 cub was sitting idling for about 10 minutes. Got on it to move it and it seemed to load up with fuel and then died. It had some black smoke when it died. Now it will only backfire and won’t run. Won’t start with crank or battery. Plug wires are secure, drained fuel to make sure it wasn’t flooded. Cap and rotor appear to be nearly new and plug wires are new. I’m stumped.

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I was thinking the same thing, that it had sipped time. Seems there has been a rash of posts lately with timing gears, or distributor gears stripping teeth and causing them to jump time.
I just wanted to make sure which ignition system it had before I gave advice on where to look.

(quoted from post at 19:48:31 07/29/18) I was thinking the same thing, that it had sipped time. Seems there has been a rash of posts lately with timing gears, or distributor gears stripping teeth and causing them to jump time.
I just wanted to make sure which ignition system it had before I gave advice on where to look.

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I was wondering this. It doesn’t seem like an air or fuel problem at all to me. Where it would normally start it backfires like a shotgun. I know nothing about these mags so I didn’t want to just take it apart.

Always good to check spark etc. when and if you have a problem just to be sure it is still there. As for the other things as the other guys have said it could have jumped time or even have the rotor crack and cause it to jump time

(quoted from post at 14:32:20 07/29/18)

(quoted from post at 19:48:31 07/29/18) I was thinking the same thing, that it had sipped time.
I just wanted to make sure which ignition system it had before I gave advice on where to look.

Click to expand...

I was wondering this. It doesn’t seem like an air or fuel problem at all to me. Where it would normally start it backfires like a shotgun. I know nothing about these mags so I didn’t want to just take it apart.

Click to expand...

"Seems there has been a rash of posts lately with timing gears, or distributor gears stripping teeth and causing them to jump time."

I've noticed that, too, but has even ONE posted back that they found the problem and it was actually "stripped" gears"?

Some other possibilities... moisture in the "distributor" cap, or "carbon tracking", or stuck valve(s).

If it DOES seem to be the mag or timing, you can peruse the factory manual for your "J-4" mag at the link below, gives troubleshooting and timing procedures.

You will have to copy the link and paste in into the address bar of your browser.

http://farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-1012%20Electrical%20Equipment/index.html

Look at Pages 4, 5, and 6.

http://farmallcub.com/rudi_cub/www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-1012%20Electrical%20Equipment/index.html

I checked for spark. I do have good blue spark at all 4 plugs however it does not seem to be in sync with the engine. I have yet to get into the magneto. I did check to make sure the mag was not loose on the engine losing time and it was nice and tight.

There has been a least a couple that posted back. One with a stripped gear at the base of the distributor and I believe another that actually had the governor and cam gear stripped.