Cub Farmall timing/spark

Neighbor needs help getting his Farmall cub to fire. He says he has 3/4 spark coming out of the top of the coil, but questions whether it is getting to the spark plugs timed correctly. I told him I would help a bit to get it running. First, he did have it running at least enough to get it backed out of the shed. He says it seems cold blooded and will not respond to rapid throttle advance. There are two timing marks on the crankshaft pulley and two pointers. The magneto has been converted to battery power. Ok, where should we begin to make sure this thing is timed correctly. Any help is appreciated. Remember the magneto has been converted to a distributor with an external coil and of course the 12 volt battery. This might be important as well regarding the type of magneto - the rotor in the old magneto sits on a little stud and is driven by a gear. The coil is also 12 volts. Thanks.

get number one cylinder up on compression check to make sure the rotor button is pointed at the number one wire

Timing almost NEVER just jumps out of place unless he has messed with it. More likely to a carb problem. Easy way to check that spark is getting to the plugs if find an old plug and widen the gap to as close to a 1/4 inch as you can and one by one put it on each plug wire making sure you put each plug wire back to where it had been and spin the engine over each time

I agree with Old, timing is likely not off unless it's been messed with. Timing is one of those things that if it is set correctly, it stays that way unless something happens to it mechanically (breaks). If that happens, it'll likely not run at all.

Won't respond to rapid throttle increase sounds like a carb problem to me.

The problem is my neighbor tore it apart. Rotor is off and now not meshed to the gear. Why are there two timing marks on the crankshaft pully?

what is 3/4 spark? it obviously has to timed to run as you said it was running. its just to get it timed correctly now. get number one cyl. on compression at TDC WITH IT ALIGHNED to the correct marks. pull off dist cap, loosen dist, turn on key, rotate distributor a bit in the direction the rotor turns, then go opposite direction till the points spark on the opening of them , tighten dist down and your done. you can do the same thing with a piece of paper between the points with the key off. once you can pull the paper out when turning dist in oppositte direction your done. i do it this way all the time , plus have checked my work with a timing light and its dead on the money. nothing hard and you dont need a timing light to set static timing. then you adjust the carb once timing is set, not before. its a hand in hand thing. also make sure the points are gapped correctly first. ooh dam magneto it is u say... well just as easy turn the engine till you hear the mag snap then look where the timing marks are. the move mag accordingly . example,.. if the mag is tripping retarded to marks just advance the mag a bit at a time and keep check where it snaps till you get it where you want. tryed to keep it simple. mag is .013 setting on points. dist is .020

or retarded timing.

1/4 inch spark as in the spark at each plug wire will jump a 1/4 inch gap between the wire end of the wire and ground as in the engine block. NOT 3/4 inch

If crank pulley marks are factory marks, one is likely TDC. The other is likely a certain degree before top dead center.
If they were filed in by somebody (not factory), they could mean anything.

If the rotor gear is un-meshed, it'll have to be re-meshed correctly. And it can only go one way. That is not where you adjust the timing.

Go to the IH topic section and see my reply in the post ..52 Cub very week spark.. that should lead you to some very valuable reference material to help you with this problem.

it is still a mag and they fire on tdc no such thing as advance timing. You want to play with that go get a dist. If it starts it is ok or it wouldnot start so you have other problems just let the mag alone

You my friend are all mixed up. Mags on the Cub fire on TDC AND THERE IS NO ADVANCING THAT. I have 6 mags on the As and B tractors that i have and have had for many many yrs and that is just the way they work just because he has external coil it is still a mag because the way it is driven

If you would like to talk through this issue email me. I will give you my phone number. We have a bunch of Cubs. [email protected]

While you can adjust the START TIMING on a magneto so it fires at TDC where it needs to when starting, there's no RPM based (or vacuum etc) advance, its firing EITHER Start (TDC) or Run (fixed advance) timing period. Get the number one up on TDC of its compression power stroke and thats when the mag needs to fire for starting. This is the same regardless if its been converted from a mag to battery powered external coil ignition, it needs to fire at TDC for best starting

John T NOT an IHC mag expert NO WARRANTY see what Bob M or Jim have to say

get the rotor gears lined up on the tower so it fires at the tower. those marks are for the dist and not the mag. The mag fires at TDC then when engine runs goes to 30 something advance but still fires at TDC when cranking till engine runs

yes i know it fires at TDC. i am giving reference as if retarded from TDC mark .