The 1919 Roadster's running rough. I decided to ground each plug to try to figure out which cylinder was giving me trouble. When grounding number 3, there was no difference how the engine ran. When I take the plug out and turn the engine, I see a spark. Also there is arc coming off of the top of coil that goes to cylinder 3. Am I not getting enough spark to the plug while it's in the cylinder to ignite the gas? What causes the arc?
It certainly seems like there is a problem with that coil. Try shift the coils and move it to another position - does the problem move with the coil?
If so, it's settled. Try another coil and/or fix the offending one. I would expect a bad capacitor so it's probably rebuild time.
If coil swapping does not solve the problem then do a compression check on the cylinder.
Compression in all cylinders is in the 40s.
Is the arcing coming from the coil contacts, or the contacts between the coil and the coilbox? If it's coming from the coil contacts then the coil needs a rebuild along with the other three coils. If the arcing is within the coilbox, then you need to replace the wood with something better ... and check that your plug wires are good too. If high voltage can't get to the plugs it will start looking for another path. Roger gave you the best advice for narrowing down the problem fast - move the offending coil to another position.
We had a guy on our last tour that had the same problem. We pulled all the plugs and they all sparked. Nothing fixed the poor running. We then changed all four plugs and it ran like a champ. PK
Coming from the coil contacts.
I agree with what the others have said re: switching parts around. Do it in a controlled manner, i.e. switch one part at a time. First the coil since it is easiest, then the plug, then the wire. See if the miss follows any of those parts and then replace as necessary. I'd bet you $100 you'll find it quickly with this method.
Swapped coils and now cylinder 3 is firing and the cylinder I put the suspect coil in is not firing.
I figured the cap is bad so I rigged one I found laying around (a 630v 150m .22uf cap not correct) to the outside of the coil (not the right way to do things I know)
and It now runs on all 4. Than I thought (afterword of course) will this damage anything?
It will work fine until you can make permanent repairs.
Yeah it was a spur of the moment thing. I just
wanted to hear it run on all 4 for the first time since I owned it.!! Thank you
PS; I didn't eliminate the original cap inside, ok? Jon