Farmall Cub

I tried to start her last night for the first time since the rebuild with no luck The starter turns the engine over very smoothly. I have a temporary gas tank set up. I pulled the wire from the coil and have good spark. I pulled a spark plug next and have NO spark. What am I missing?

Does the kill switch ground the system to stop it or the other way around?

Help please!

Ken, since you mentioned kill switch I assume you still have a magneto. The kill switch grounds the points and completely kills the spark. Did you correctly time the governor gear when you reassembled the engine? Have you checked that the rotor is pointing to the correct wire? Rudi has a magneto timing guide on his website. Also check that the pinion gear (drives the rotor) hasn't broken, they are getting old and seem to be regularly failing.

Ken, the kill switch grounds the points to stop the engine. Your problem lies in the distributor. If the mag is generating a spark (which you have confirmed) then the problem is delivery of the energy to the sparkplug. First of all, check your timing. Pull the distributor cap and confirm that the rotor is spinning as the engine cranks. The mag is delivering spark to the distributor cap, the rotor delivers it to the plugs. The spark must be delivered at the proper time as the rotor tip passes the lugs on the cap. Make sure your coil wire is firmly connected to the cap center post.

John & Bigdog,

Yes, I have rebuilt the J4 magneto and have good spark from the coil wire. I matched the timing marks up dutinrg assembly.
I pulled the cap off and watched the roter turn with the engine. It seemed a little jumpy not smooth but it was turning. Even if it wasn't timed correctly I should see spark from the plugs, right?

I had the same problem with a farmall A. I had the timing off from the rotor cap to the dist cap off. It was sparking in-between the lugs and I had no spark to the plugs.
Bring it up to top dead center firing strock and pull the dist cover and see if it lines up with the rotor cap. you might have to play with that.
Chad

Ken (48 Cub) wrote:John & Bigdog,

Even if it wasn't timed correctly I should see spark from the plugs, right?

Wrong! The rotor must be pointing to one of the towers when the mag trips, even if the wrong one in order to have a spark at the plugs.

If the spark doesn't have a path through the plugs it can jump internally to the coil, and possibly damage it. The J-4 mag does not have a safety gap to prevent damage.

The impulse should never be allowed to trip without an external path for the spark.

George, your'e right. That was a dumb statement. It's got to be the timing. Bigdog will back me up when I say that I really struggle with the electronics. I guess my brain is just not wired that way.

I will check the timing tonight and report back tomorrow.

Thanks,

be sure that while testing with the distributer cap off, that the mag is turned OFF, otherwise, damage to the mag is possible. you might have timed the motor 180 out by thinking the dist turns CCW. easy to test, swap plug wires 2 and 3 and try to start.

Ken:

Forgive me for saying this, but it is nice to have company in the "not much good at electronics stuff" boat

Have a look again at the manual, and then at The Best of H.L. Chauvin's articles. Between the two of them, that is how I learned to time Ellie properly.

I would bet dollars to doughnuts that your problem is most likely timing, and you are probably 180 degrees out. I had to do it dozens of times before I got it right.

Hope this helps a bit.

Remember 1 revolution is 2 times pasts the timing mark

I had the same problem, Thought I had timed it perfectly when I rebuilt it, only to find I was out 270 degrees the wrong way!!. The HL Chauvin article is very helpful.

Dogman wrote:Remember 1 revolution is 2 times pasts the timing mark

I assume you mean 1 revolution of the rotor takes 2 revolutions of the engine?

yes that is what I mean
last week I put a mag on one of my mutts turned the crank around one time to the timing mark and couldn't trip the impulse so I tore off the governor checked the timing marks came up the house read the manual grabbed my right ear with my left hand my left ear right hand pulled real hard and wiped the brown ring off my neck again

Again Please bring it up to top dead center with compression stroke.
Then mark where #1 is from the cap to the dist cap base. take off the dist cap and see if the rotor cap pointer lines up with #1 tower on the dist cap.
This will tell you if it is right. You may have your mag timed right but you might note have it aligned to the dist cap.
Chad