'34 F12 Starting/Timing Issue

I'm having a terrible time getting this engine to start. It'll fire once in a blue moon but has yet to actually run.

Rebuilt engine and cylinder head, rebuilt carb, rebuilt mag from Nebraska Kirk. New plugs and wires from Brillman. Attempting to test run off a gravity fed temporary tank. I've even went so far as to spray gas staright down the carb throat with a windex bottle.

The owner's manual is quite clear that the impulse should trip at TDC or never anymore than 25/32" of a flywheel inch after the DC 1-4 mark has past the register mark on the flywheel housing. Mine is tripping well beyond that, perhaps nearly double. Way, way late in my mind. You can feel the piston has already started back down once it trips.

If I set the mag to 1:30 or so it doesn't seem to trip until about 3:00 or so, way late. If I turn it until it's about 12:30ish it's "against the pawl" ready to fire. If I put the cap back on it, crank it on over when the impulse fires it's on the trailing edge of the distributor block contact, still to late. The piston has already started back down. Seems like the impulse only engages twice per revolution.

I know the crank and cam are timed correctly, even took pictures of it before I put the cover on it. My attempt at keeping myself from second guessing myself down the road.

I'm beginning to wonder if I should just forget about the DC 1-4 mark and set the mag at the point I feel the piston has reached the top of it's stroke?

I'd appreciate anyone's suggestions or input.

well, here is how I time an F series mag to engine. loosen all 4 spark plugs and remove #1. Turn engine over until you feel it coming up on compression on #1. STOP. Take a 1/4" wood dowel rod, and place into plug hole, until it rests on the top of the piston. continue turning engine over until you FEEL TDC. If you overshoot, no crisis, just turn the engine backwards a little. When you are sure you are on TDC, then take the mag, and using a finish nail (10p works best for me), insert it into the oiler on the face of the impulse cover until you catch the impulse pawl, and hold it up. If you have the older style mag, there will be a little tab that you can pull up on to disengage the impulse. you can now spin the mag drive without the impulse engaging. make sure the spark advance is in the full retarded position.

Now, with the distributor cap off, rotate the drive until the center the brass insert in the rotor is oriented to the #1 plug wire post on the cap. Without disturbing the position of the mag, now place it on the mount about 1" away from the drive on the governor. Take out the 2 1/4" bolts holding the coupler on the governor drive. Slide the mag and the coupler disk over until it meets the governor drive. Rotate the coupler on the governor until the mag, coupling disk, and governor drive all engage. Locate the 2 holes in the governor coupler that you can thread the 1/4" in bolts into without moving or disturbing the orientation of the mag. They should be 180 degrees apart. Tighten bolts and install mag mounting bolts.

You are timed and ready to go.

Tom,

Thank you for your response. I had a county fair board meeting last night and didn't get home until late, but I couldn't stand it, I had to try.

I hadn't read your post before I went up to the shop last night, but that's pretty much what I done. I just said to heck with the timing mark on the flywheel. I brought no. 1 up on compression until I could feel with my finger that it's upward travel had stopped. Then I took the mag back off, reset it the impulse, recoupled everything.

I fogged the carb with gas from the spray bottle. About 4 cranks and it hit, sprayed it again, four or five more it hit again. Shot it again with gas and on about the third or fourth crank it fired and ran, perhaps 5-10 seconds.

I think I'm headed the right direction now. I'll continue with temporary fuel tank in another evening or two and see what happens. Thanks again...

you are on the right track. Remember, the carb fuel bowl MUST be full of fuel for these to run. The IHC #10 carb (which I believe to be the right number) can be VERY cantankerous. However, when they are right, they will fire right up and run......and run well.

make sure the fuel bowl is full. There should be a drain on it. crack the stopcock valve open and see if you have fuel. if you are using a gravity feed, if it is dry, the float needle valve may be stuck shut. If you have fuel, then it should fire and run.