Ignition Problem or Carb Problem

[koates]

As I have stated previously you can measure voltages and resistances till the cows come home but to really know what is going on in the coil primary circuit the current draw needs to be measured with the engine not running and dist timing points closed so as to complete the circuit and then with the engine running at idle speed. Use a good quality digital multimeter with a 10 amp capability. Engine not running with ignition switch ON should be 3 to 5 amps. Test quickly so Ign. is not on longer than a minute. Run engine at idle speed and reading should be about 2 amps. If you are in this ball park then all is good. These readings are for both 6 volt and 12 volt systems. Regards, Kevin.

[Tinker]

I don't know anything. But Pertronix?


Spiral wound wire for electronic ignitions, solid for points.

[drolston]

Originally Posted by HD Rider

I've run into the same thing with old Harleys. Electronic ignitions use lower resistance coils than breaker point ignitions. Put the ballast back in and try it.

Put the ballast resistor back in the (1.5 Ohm blue Bosch) coil circuit. Coil volts read 12v with points open, 10.5v with points closed. That is with the resistor cold. Does that sound right?

The bad news is that the engine will still barely run; stumbles; won't take throttle and build up rpm past about 1200.

Will swap condensers next. It is not shorted, but if the capacitance is too far off, the mismatch with the inductance of the coil could cause a problem.

Will report back when checked out.

[tubman]

For what it's worth, we made the first prototype "Trash Can" reproduction condenser with a .047 micro-farad capacitor (it was all we had that would fit). The engine (a flathead, of course), ran fine. I wouldn't make a large bet on point life, but that's really not that important. Unless you are concerned with the difference in point life to be 20K miles vs 25K, don't worry about the exact capacitance. A .22 and a .36 are virtually interchangeable on these engines.

If you are going to test condensers, heat cycle them. (You should also check for voltage spikes above the rated value of the condenser being evaluated. I don't know how to do that, so I use capacitors that are designed withstand 600 volts, which seems to be enough.)

[Bill OH]

You state that the spark is erratic when cranking like it is not hitting every cylinder. I still think that the points need looking into for spring tension and closing or binding. Points hanging open? I have had that happen - tightened the spring tension solved the problem. And you might put s drop of oil on the pivot point.

[drolston]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by drolston

You are right. Not the carbs. Took all three carbs apart and found nothing that might cause flooding. All floats set correctly. Main jets all firmly seated. All power valves seated and little pop-ups working freely. Not entirely a waste of time. I did find and fix one leaking main jet plug, and all carb bases with risers really needed tightening.

Again, after the carb check, it ran at fast idle a little roughly, would not wind up with throttle; started hesitating, then after about five minutes just quit. No black smoke, new plugs not black or wet.

I am running a brand new Bosch blue coil which I measured as having very close to 1.5 Ohms. That should not need any other resistor, right?

When I set up the new distributor, I put on a new condenser. Could that cause it to run rough and die.

The spark from the coil wire is blue and will jump almost half and inch when cranking, but it looks a little thin and puny. And it seems erratic when cranking, like it is not sparking every cylinder.

Suggestions?

To answer my own question and put an end to this comedy or errors, I can definitively state that a bad condenser (New original-look-alike from Macs, part #32-882338-1) can show a fine spark when cranking, and then not run worth a damn. When this saga of missing and lurching started (ultimately traced to spiral wound spark plug wires with internal/invisible broken connectors), I bought a condenser from Tubman. Thought about returning it because it was too big to mount at the normal spot on the side of the crab distributor. In the mean time I went through the distributor and replaced the condenser with the Mac's thing). Then I went down the carburetor rabbit hole and fixed some little things there; then I put the ballast resistor back in the circuit. Still barely ran, and after a few minutes would die.

With good advice from members of this board, I pulled the Tubman condenser out of the "return" pile and mounted it so it connects to the coil end of the black wire to the distributor, instead of on the distributor itself.

Still need an all out road test, but in the garage it is running like a champ!

Thought I knew something about flathead ignition. What I did not know is that a nice blue spark when cranking does not necessarily mean that the problem with running rough is in the carburetor.

The other thing I learned is, like starter switches, never buy a condenser from just anywhere.

[JayChicago]

Good news. Sounds like that condenser would work on start up but then fail immediately.

But I think you are not done yet. You said: "I am running a brand new Bosch blue coil which I measured as having very close to 1.5 Ohms. That should not need any other resistor, right?" With your 12V, that will allow too much current, will cook things. You want about 3.0 ohm, either a 3 ohm coil with no resistor, or use your coil with a 1.5 ohm resistor.

[tubman]

Thanks, "drolston". I have been looking for that returned condenser for a while, but it never showed up. I guess I now know why. I'm glad it worked out for you.

"squirrel" on the "H.A.M.B." did a little research on the "intermittent condenser problem" mentioned and found that the connection from the lead wire to the the internal workings of the condenser was faulty. It was held in contact only by the crimping together of the condenser body. It would be fine when tested statically or with the engine not running, but when the engine was started, the vibration from the running engine would cause the connection to become intermittent and fail. This why you can run into failures with multiple new condensers.

I do mine differently.

[JSeery]

Originally Posted by JayChicago

Good news. Sounds like that condenser would work on start up but then fail immediately.

But I think you are not done yet. You said: "I am running a brand new Bosch blue coil which I measured as having very close to 1.5 Ohms. That should not need any other resistor, right?" With your 12V, that will allow too much current, will cook things. You want about 3.0 ohm, either a 3 ohm coil with no resistor, or use your coil with a 1.5 ohm resistor.

See post #23.

[Ken hash]

I’ve been reading these posts and when I saw erratic spark I thought the problem might be the distributor cap. A crack in a cap can be hard to see and a manufacturer defect even harder. What ever it is I know you can solve it. Good luck

[Bill OH]

Pleased that you found the problem. I have had straps break off condensers, and a new condenser fail with a no start, but your problem was an education for me too.

[drolston]

Final report. (maybe)

Did the road test and it runs like a scalded dog. Wound right up to 4800 in first and second without a miss. Got a little spark knock at full throttle in second. Because that "ping" could have been detonation, I first will go back on the heat range on the plugs from the NGK B5HS to the B6HS. If that doesn't take care of it, I will pull back from 4 degrees advanced to 2 degrees advanced.

Thanks again to all who walked through this with me.

[tubman]

Since you have a modified engine (heads, carbs, etc.) I will indulge in a little shameless self-promotion and say it looks better too.

[drolston]

Originally Posted by drolston

Final report. (maybe)

Did the road test and it runs like a scalded dog. Wound right up to 4800 in first and second without a miss. Got a little spark knock at full throttle in second. Because that "ping" could have been detonation, I first will go back on the heat range on the plugs from the NGK B5HS to the B6HS. If that doesn't take care of it, I will pull back from 4 degrees advanced to 2 degrees advanced.

Thanks again to all who walked through this with me.

To answer my own question and close out this thread, the cooler B6HS plugs did not solve the pinging problem, but backing off 2 degrees advance did. The B5HS plugs go into the parts box in the trunk as spares in the event that the cooler plugs get fouled somewhere along the way. Another lesson learned is that once fouled, cleaning and torching the electrodes may not bring them back. Better to pony up for new plugs.

[FLTHDCPE]

I'am running a "H & C" ignition with ( 2 ) "Bosch Blue" coils and two "Tubman" condensers. Engine temp got to 200 dg. shut off and would not start. ( No fire at the plug.) Engine cooled down to 180 dg. and fired right up and ran fine.!! We are still looking.??