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Discussion Topic:
1936 idles great, misfires at load
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maruapo |
05-05-2019 @ 8:19 AM
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Member
Posts: 6
Joined: Mar 2011
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My 1936 Ford flathead 68 6v is about as original as it comes. I had the distributor out a couple years ago, and b0th sets of points looked great, though I'm well aware that human eyes are no replacement for a distributor machine. Ignition coil, who knows what's going on but it seems fine. Spark plugs new, and every test of the spark results in the desired 1/2" blue flame; the plugs have no fouling. Anyway the car runs great. Idles beautifully. When parked, you can race it to high RPMs and it doesn't miss at all. But get it on the road, and put any stress on it whatsoever, and it misfires quite badly. I suspect distributor or coil. Heck just about everything related to ignition is suspect, but since it has no problems except at load I'd rather not rip rebuild/replace everything if it's just one little thing. Before I send the distributor to be rebuilt, or get a coil rebuilt, any thoughts on what's going on?
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TomO |
05-05-2019 @ 8:38 AM
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Senior
Posts: 7264
Joined: Oct 2009
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Your problem could be insufficient fuel delivery. This condition shows up when driving at highway speeds as a miss or the engine dies. To check fuel delivery, you need a graduated 16 ounce or larger container to determine the amount of fuel delivered in a measured time. Disconnect the fuel pump line from the carburetor and direct it into a graduated container. Crank the engine long enough to get 2 ounces of gas in the container and then continue cranking for 15 more strokes of the pump. The pump should have delivered 6 more ounces of gas. Insufficient fuel delivery can be caused by a vacuum leak, plugged flex line, worn pivot in the pump arm, stretched diaphragm, plugged fuel line or tank pickup, plugged tank vent or wrong gas cap or a worn push rod. The push rod should be 8 7/8" long for the cast iron manifolds and 7 7/8" for the aluminum manifolds. It travel is about 3/8".
Tom
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maruapo |
05-05-2019 @ 4:17 PM
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Member
Posts: 6
Joined: Mar 2011
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Thanks for the suggestion, TomO. If you had to wager, what are the odds that instead it's a bad coil? I had a boat once that did this when you gunned it and it turned out to be the coil, so my head goes right there
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MG |
05-05-2019 @ 6:53 PM
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Senior
Posts: 1262
Joined: Nov 2009
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Replace the condenser....
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4dFordSC |
05-05-2019 @ 7:11 PM
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Member
Posts: 266
Joined: Oct 2009
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Coil or condenser. Send the coil to Skip Haney for rebuild (http://www.fordcollector.com/coils.htm), and replace the condenser (NAPA IH-200 works well with flatheads).
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carcrazy |
05-05-2019 @ 7:56 PM
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Senior
Posts: 1682
Joined: Oct 2009
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Suspect inadequate fuel delivery. The fuel pump is not providing the fuel required to run the engine when it is under load.
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TomO |
05-06-2019 @ 6:51 AM
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Senior
Posts: 7264
Joined: Oct 2009
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Based on your post that you had a nice blue spark at all plugs, I feel 99% confident that it is not the coil or condenser causing your problem.
Tom
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sarahcecelia |
05-06-2019 @ 7:58 AM
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Senior
Posts: 1194
Joined: Mar 2013
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I HAVE THAT CAM IN ONE OF MY '50'S, AND 390 HOLLEY 4BBL; AND IT DEMANDS AN ELECTRIC FUEL PUMP TO DELIVER ENOUGH FUEL!! THE STOCK PUMP WON'T PUMP ENOUGH TO FEED IT. I BLOCKED THE PLACE WHERE THE STOCK PUMP GOES, WITH A POLISHED PLATE I MADE.
Regards, Steve Lee
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37RAGTOPMAN |
05-06-2019 @ 11:56 AM
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Senior
Posts: 1969
Joined: Oct 2009
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hi 1936 it sounds to me like it is a IGNITION PROBLEM, loose connection, bad ignition resister, check it for getting real hot, try a jumper lead across the 2 terminals on resister, if it runs better , it is most likely a weak coil,and resister, also, you can try applying a ICE BAD, on the coil, yes a ICE BAG, I know it sounds stupid, but it does work,by cooling the coil HOW DOES IT START HOT ? ??? try changing the CONDENSER first, when it starts dying out, did you try pulling the choke out 1/2 way,? If it make a difference it might be fuel but I doubt it also just try pulling a few plugs out and see if they are sooty , how old is the ignition wires, at night see if you see any cross firing on the metal conduit Or spray water on the wires, and see if they arc, my 2 cents 37 RAGTOPMAN
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supereal |
05-06-2019 @ 2:36 PM
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Senior
Posts: 6819
Joined: Oct 2009
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I Agree that a weak condenser is a suspect. I keep a condenser with clip leads in my road kit as a precaution. Another place to suspect is the metal conduits between the distributor and the plugs. If your plug wires are original, or very old, it is likely they are cracked where you can't see them inside the conduits, causing shorts. A good grade of metal core plug wires is a desirable investment, in any case. Same is true with old distributor caps. Any cracks will result in carbon paths that produce misfiring.
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