I have a miss at a high RPM,and my magneto mysteriously stop working last fall. I read through some posts and more than once some of you guys said they had problems in the timer harness. So i started testing the harness, took the timer off and put my tester on one of the terminals and got continuity on all four top posts of the coil terminals. This happened with all terminals on the timer. I'm puzzled, there should not be continuity through the coil box should there?

If you're just checking continuity, then yes. All the the terminals on the coil box will show continuity. If you look at a cross-section of a coil and follow the circuit of the primary and secondary windings you'll find the reason why they show continuity.

The timer provide the ground circuit for the coils. Positive from the battery or AC from the magneto is controlled by the ignition switch and is supplied to all the coils simultaneously. The timer determines which coil will get ground and thus completing the circuit to fire that coil.

It's not uncommon to have a high rpm miss when running off battery. The question is how high? Have you tried to clean the magneto post and/or test the magneto output?

Thanks Ken,

Appreciate it, I'll have to do the 1156 bulb test with volt meter next. I've tried a new magneto post terminal, still nothing, I looked for the in car magneto charge proceedure on the forum, but haven't been able to find it, would anyone have the link to that post. I guess I"ll do that as a last resort.

Murray

I had a harness failure on O2O trip which manifested itself in a way similar to what you describe. The way I found the failure was to check contunity in the harness, but only in the harness. Connecting a VOM to one wire-end gave contunity readings on all four of the four wire-ends at the other end of the harness(and I assume in the three remaining ends on the end I first connected to, but I didn't check that). Apparently there was a "soft short" in the harness so when one wire was activated, all four were activated to some degree. I assume this robbed juice from the needed wire and gave weak spark at the plug. The car would run OK at idle, but not very well and at higher speed, the issue became quite noticeable. This was a relatively new harness and must have been defective. I installed a new harness and all was well. Steve Boyd

I just made a new harness for the same reason, high speed miss. I found intermittent continuity at #2.

Guys,

I worked on a friend’s 1919 coupe that had a miss and it ended up being the timer wire harness. The problem was in the terminals, which were/are just crimped on. They either became loose or dirty causing intermittent contact while the engine was running. I solved this by cutting off the terminals and soldering on new ones. I remove the colored plastic covering (just twsited it off)on the crimp end of the terminal, insert a small piece of black shrink tubing over the wire, soldered the terminal, then slid the shrink tubing up over the solder connection and shrink it. The finished product looks like original but you never have to worry about a loose connection again.

Mark

Yup, I've seen that before.

Thanks Guys,
The harness that's on the car has ends on it (attached to the timer) which are not very good, and what I thought was semi broke. So the lose crimp on scenario makes a lot of sense now. I've bought a new harness and think i'll try soldering them or crimp them harder to make them more secure. I'll report back, thanks again i've got a good feeling about this now.

Murray

Ok guys, you haven't failed me yet.

My high RPM miss seems to be gone, and the fix was putting 5/16 rubber fuel line level on the back side of frame but as straight as i could get it (yet to be road proven). The previous line was modified to have brass compression fit fittings on a 1/4" line, but that made the interior of the line very small maybe 1/8". Along with the routing, i believe i was starving the carb.

I'm counting on you guys again and hopefully the last time before my perfect drive, if there is such a thing.

I need to diagnosis my magneto.

1. switch seems to be fine- but not sure how to test it.

2. did the 1156 backup light test. It did't light at all, and i got a 3.1 volts across the load.

3. i took the bottom engine pan off and only noticed maybe a little angle on the back main babbitt.

4. put a pry bar on the front of the crank. It didn't seem to move.

Finally I think I may of inadvertently put battery power to the mag this winter but i'm not 100% sure.

Counting on you guys. This is my 24 coupe that was bought new from my great great uncle. I've been plagued with minor problems for twenty years. I'm so determined to get it on the road properly this year and it seems reachable now.

thanking you guys in adavance.

Murray