| Flatbob | -- 06-05-2012 @ 11:04 AM |
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My '36 has been hard to start, rough running and backfires at higher engine speeds. Pulled the plugs and 5 out 8 plugs have carbon deposits and cylinder plugs 6,7 & 8 are perfectly clean; if those cylinders aren't firing would this explain unburnt gas causing the backfire in exhaust system? Any ideas as to why 6,7 & 8 won't fire?
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| supereal | -- 06-05-2012 @ 11:24 AM |
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It appears, from your photo, that you have an ignition problem. It could be a loose or incorrect distributor cap on either or both sides, caps with cracks or carbon paths, or poorly seated spark plug cables in the caps. Inspect the rotor to see if there is obvious damage. We are seeing serious problems with repro caps. Many don't fit properly, which can cause your symptoms. Some require filing to fit properly. If all plugs showed soot, I'd suspect the coil or condenser, but yours don't show that. If you have non-metallic plug wires, I'd suspect them, as well. You didn't mention any recent work or replacement parts.
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| Flatbob | -- 06-05-2012 @ 12:48 PM |
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Super, am going to pull distributor caps & do an inspection. The distributor body is all original, the coil has been rebuilt & new condenser. The plug wires are 15 years old but the car has less than 250 miles.
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| Flatbob | -- 06-05-2012 @ 2:27 PM |
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Super, bare with me here but am a little confused about condenser(s.) Could a bad condenser be responsible for firing on 5 of 8 cylinders? In the enclosed picture it appears I have two condensers; in my '36 repair manual it only shows one condenser. Upon inspecting the inside of the distributor everything appears to be as it should, points are clean and moving, rotor looks okay & no carbon tracts.
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| TomO | -- 06-06-2012 @ 9:43 AM |
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All of your failing cylinders are on one side of the engine. Because you have the distributor out, I would first check that the wires are seated in the cap, These sometime get pulled out when installing the caps. Next I would check to see that the cap on the failing side seats correctly into the distributor. As Super said, some caps have swollen and do not seat. You should have about .010" clearance between the contacts on the caps and the contacts on the rotor. Much more than this and you will get a misfire. Your second condenser is for radio noise suppression. Tom
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| supereal | -- 06-06-2012 @ 12:12 PM |
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Tom and I are on the same page, as usual. The extra condenser might be for radio noise suppression, but should not be connected in parallel with the ignition condenser. The use of condensers for radio static is more effective on generators, etc. Non metallic carbon fiber spark plug wires were designed to help, but too often they create more problems than they solve. Most radio static enters on the radio power wire and/or the antenna. The radio in my '47 was converted to AM/FM. The FM band is virtually static free.
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| Flatbob | -- 06-06-2012 @ 2:46 PM |
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Am going to look more closely at the caps & contact points, will advise.
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