mag/coil conversion got me stumped--HELP

The impulse coupler gave up on an FMJ mag on my rarely used Allis Chalmers B, so I converted it to battery/coil ignition. I have a great deal of experience with battery ignition but not much on mags. I disconnected the mag coil wire and removed the coil to cap rod, drilled the cap to accept the coil wire, wired a switch to the coil and hooked the negative side of the coil to the grounding lug on the side of the mag to the points, timed it to the required 30 degrees advance, have 1/2 inch blue spark, cranked it over and it immediately fires up runs a couple seconds, then immediately shuts off. I've been pulling my hair off and on about this for a week, tried 2 different (bad)mags with the same results.
My understanding of the mag is that the impulse coupler retards the spark for starting while also spinning it much faster to generate more spark. Have also searched the net to see if these mags have some type of built in advance that would advance the spark way to far and prevent firing as rpm's rise. It seems that if that was the case, it would knock, try to kickback and backfire, but it shuts off as if the switch was turned off. It will immediately fire up and quit again.
I could yank and install this mag in my sleep now and it's got me stymied. Any thoughts will be appreciated.

Maybe spark is not your problem. Pull the gas line from the carburetor and let it flow for one minute. Should have steady stream. Dump gas back in tank if clean.
Dave.
_

Are you still getting fire to your sparkplugs after it quits running? If you are I think you have a fuel problem. Pull off a plug wire when it quits running and check for fire. You will probably need a helper. Hal

If it shuts off after you let go of starter check your source of power to coil. Does it continue to run (idle it) while starer is held on?

Sounds like the ballast resistor in the run line is bad. Engine will start then stop as soon as you let go of the starter.

No fuel problems, no run line problems as starter switch is manual foot operated, power direct from battery with no resistor (yet). Spark just shuts off as soon as it starts running, will not idle. tried 2 different mags, 2 condensers and 2 coils?????????
Seems like it has to be in design of the mags??
Maybe I'll have to totally disassemble one to see if something could short out at rpm's??

Still stumped.

Why not get your mag fixed..a new impulse, if that was the problem, is redaly available, Mag
parts are still available..there are ads for
suppliers in most of the tractor hobby
magazines, Y/T even has a few parts. Magnetos
are not obsolete, you can still buy brand new
ones

That may be what I wind up doing but one mag throws no spark at all, the other very weak spark (tickles your finger but won't arc, thought possibly demagnetized armatures as coils/condensers are OK) and I thought with as little use as the tractor gets, I'd bypass it all with the coil conversion.

Thanks,
Smiley

Sounds like you are just trying to use mag points to switch the coil that you added. You may (didn't say) still have mag internal coil still connected to your points. If so try disconnecting it.

Yes, using mag points and mag coil is disconnected.

Check the ignition switch to see if it is still supplying voltage after it moves from the start to run position.

Will it idle and dies only at fast throtte?

Are you sure the impulse coupling is not hanging up a little? The reason the spark advances at higher speeds is that as the engine RPM increases the centrifugal force of the impulse mechanisms moves outward and keeps the impulse from working so it then operates the points without the delay caused by the impulse mechanism.

I am having a little trouble visualizing your connections
Did you drill the center of the cap so that the coil secondary would plug into the front?

What condenser did you use? The condenser is sized to control the fly back from the ignition coil, you should use the condenser specified for the coil you are using not the original magneto condenser.

Look at the points, any change in color or pitting?

Any evident of pitting or transfer of metal from movable point to stationary point or vise-versa?

Did run jumper from bat to coil eliminating switch, no change.

Dies after running a few seconds at idle or throttle
Used 2 different mags, one with good impulse, the other bad impulse, did initial timing at 30 degrees as specified on both, tried retarding and advancing spark by moving rotor 1 tooth off in each direction.
Yes, removed the rod and drilled through the brass fitting and front of the cap, then tapped the brass and installed a bolt with the coil wire attached. Tried both solid and resistor coil wires.
Removed and ground/polished points to new condition.

Now, you mention condensers. I used the mag condensers and also tried an old automotive condenser but not necessarily matched to the coil so there is a possibility.
The only other thing I thought of trying was running a wire from the coil directly to the points rather than using the shut off lug on the side to eliminate any possibility of grounding out from vibration or ??
I won't get back on it for 2 or 3 days as in laws came in from Canada this afternoon.

Thanks to all for suggestions so far and if anyone thinks of different possibilities, keep em coming. It ticks me off because I know what it's supposed to do and can't make it do it, but I'm stubborn enough that with your help, will get it eventually. Even if I have to wind up learning how to rebuild mags.