59AB miss in 1 and 2

rottenron36

rottenron36

Senior Member
Need your help again! I have a miss in 1 and 2 cylinders that I can't chase down. My crab distributor has been set up on a sun machine. Coil, spark plug wires, cap, have all been checked. Compression is within 5 psi in all cylinders. Leak down test on all cylinders is between 25 and 30 in the green. Carb has been rebuilt and just cleaned again. 3 and 4 have tan and clean spark plugs. All spark plugs are new and have been changed around. If I clean the plugs in 1 and 2 and start the engine, by the time the engine warms up, they are black. The miss is not that bad, but does drag the engine down at all rpms. I am lost as what to do next. Any help will be greatly appreciated. Thanks Ron
 
Could the plug wires be shorting in loom or bracket that holds them? Are you sure there is no carbon track or crack in the cap? Remember, electricity takes its easiest path to ground. Since it is always 1 and 2 I would try another cap first.
 
I was there when the distibutor was set up. The wires were check in the loom. The cap is a quality cap with brass terminals, with no tracks anywhere. We had spark plugs hooked up, when the distributor was set up, with no problems. NGK B6L plugs. The engine has straight pipes, 5,6,7,8, cylinders sound great. Don't get it. Thanks Ron
 
Are the plugs 'wet' black or 'dry' black? Dry is excess fuel, wet is oil. If oily wet, bad rings and/or pistons.
 
Sorry, engine has used .060 over pistons, hone, new rings, bearings, and valve job. Dry black. Even though there are no tracks anywhere. I will get a new cap to rule that out, or fix it. Thanks Ron
 
You first say they're "missing". Then later-on, you say "the miss is not that bad." Either they MISS, or they DON'T!

Have you tried (for instance) taking #1 OR #2 plug out of the head, grounding it and seeing whether it produces a spark when the engine is turned-over or run? That process (IF the plugs show NO spark) pretty-much rules out carburetors, low compressions, fuel pressure and other superfluous BS that is not relevant. DD
 
G.M. said:
Some plugs fire in free air but not under compression. G.M.
Click to expand...

True, but my scenario talked about NO spark. IF there's NO spark, the problem is PROBABLY electrical.......only methodical troubleshooting. Rule the easy things out first. DD
 
When I said the miss is not that bad, I meant the engine runs on all 8 cylinders, 1 and 2 miss part time. If you take the spark plug wire off of 1 or 2 the engine runs worse, when you put the wire back on it runs better, but still has a miss. yes all 8 have a good spark. Ron
 
Interesting. I think the "wet black, dry black" is an important question. Does it miss regardless of what the engine temp is? Does it smoke...if so...what color? Initially I was going to offer the fact that some plugs will free-air fire and not under compression but eliminated that when you said you switched them around. I've never heard of this or tried it but would sticking a couple hotter plugs in those two holes be worth a try? Just to see if it makes a difference. Sometimes when my dad was faced with things like this he'd say "Sometimes ya just gotta let these things develop"...meaning...run it till the problem becomes apparent. I know I'm not much help and I'm anxiously awaiting to hear the resolution!
 
Have read all the replys, my money is on a bad crab cap, 1and 2 are right beside each other- top two on right side of cap- just below no.1 is where the snap clip holds the cap on. I've had caps with a hair crack on the inside from the terminal through the cap to the snap clip. Let us know when you find the problem. Walt
 
Installed a standard, made in America cap, no change. Did a leak down test, all cylinders were within 8 psi in the green between 20 and 30. Did another compression test all cylinders were within 7 psi, and over 90psi. The engine has less then 2 hours of run time on new rings, hone, bearings, ground crank, and valve job. Now what? Thanks again, Ron
 
Do you have 2 other wires you could swap for 1 and 2 to test if maybe they are shorting somewhere? Remember "new doesn't equal good" anymore.
 
deuce_roadster said:
Could the plug wires be shorting in loom or bracket that holds them? Are you sure there is no carbon track or crack in the cap? Remember, electricity takes its easiest path to ground. Since it is always 1 and 2 I would try another cap first.
Click to expand...

Like deuce roadster said, if you are using looms check them. Start it at night and look for a fireworks display inside.

Lonnie
 
When a condensor first starts to fail it will usually kill a couple cylinders. Thats what we see on the tester maybe idle on all eight but then loose one or two every cycle????
Just another thought.....
 
I had a miss in my 8BA so I started the engine at night when it is totally dark, lifted the hood and watched for any electrical activity. There was a plug wire close to a metal part and that wire was sparking onto the metal part. It showed up well in the dark. Have you tried that test?
 
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