My '73 400 uses breaker points. Recently the breakerplate broke at the pivot and the vehicle would not start. I replaced the breaker plate, ground wire, points and condensor, and while I was at it I put on a new cap and rotor as well. It runs great, but I have a great amount of trouble getting a timing light to flash now. When I hook the pickup to the #1 wire it won't flash...if I move it to wires on the other side of the engine it will flash, and then I can move it back to the #1 wire and it will flash intermittently (enough to time the engine). I checked the resistance between the end of each wire and its respective cap terminal and each one is in great shape. This has happened with two known-to-be-good timing lights.

My only guess would be some kind of field is creating interference. Is it important the material of ground wire I used? I used some spare 18-gage speaker wire I had lying around.

Any thoughts?

 

so it's not the timing light. must be the cap or plug wire then. what brand cap did you get? could be a bad piece of wire or a bad crimp on the wire too? double check the wire connections by pulling the boots way up on the wire, then install the wires into the cap and onto the plugs. then push the boots down to cover the connections.

 

It probably isn't the problem with the timing light, although I might be but I would replace that ground wire, speaker wire is not intended to carry very much voltage, and I wouldn't use anything less than 14gauge wire, basically for any of the wiring in a vehicle except the speakers.

 

Hmm...

Well, I did replace the coil tonight...my original showed about twice the acceptable resistance across both primary and secondary. Plug wires are seated well. The problem is better but not fixed.

I'll try a new ground wire...is that the source of the problem? The old wire wasn't 14 gage...it was this little piece of copper wire that didn't have insulation. Is the ground wire creating interference or what?

 

are the cap and rotor high quality name brand?

 

If anyone is interested on how this turned out. I finally got the time to look at the problem again. I pulled the cap off and some of the contacts underneath were rounded off and a little burnt for the 2 weeks time I had the cap. So I got a new (different brand) one and problem solved! Thanks grclark351 for narrowing it down.

 

there might be more to it. if your dizzy is dropped in one tooth off at the drive gear, the rotor might be what they call "out of phase" with the terminal pin in the cap. basically this means that the spark is jumping diagonally from the rotor to the cap terminal, instead of straight out from the rotor to the cap terminal. being one tooth off, you may still be able to set the timing correctly without the dizzy housing bumping into something. the dizzy housing holds the stator piece of the primary ignition, and the trigger piece is on the shaft. these are the parts that actually tell the coil to fire a spark. they are also the parts that control when that happens, when you adjust the timing by rotating the dizzy housing. the relationship of the rotor and terminal pin in the cap is engineered into the whole shabang from the get go when the dizzy is dropped in so that the rotor is where it is supposed to be. it's supposed to be at about almost 1:00 when #1 cylinder is at TDC. it's possible that your new cap will burn a way very quickly also if my guess is correct and your dizzy is a tooth off? one way to check is to drill a large hole or two in your old cap and shine the timing light at the rotor through the hole with the engine running. you can do it to any #wire, it doesn't have to be #1. the important thing is that you can get a good look at it, #1 is hard to see back there. just put the timing light on the wire of the terminal where you have the window in the cap. this way you can see if the rotor/terminal relationship is aligned well.