A very perplexing problem.

Bassman/NZ

Bassman/NZ

Well-known member
My C59A engine feels like it's running on 7 and 1/2 cylinders.
It's stock except heads milled for 45thou clearance over pistons, has had new rings, bearings, valve grind and valve guides, valves set to 10thou in and 14thou ex. New Best copper gaskets, dissy rebuilt by Bubbas (including condenser) and points set at 15thou. New plug leads and plugs set at 28thou, Ford 94 with mating surfaces flat, 50thou jets, all orifices blown out, leather plunger, power valve checked and seating, float set right. Bosch 12v coil with external resistor.
Runs best with the advance plate (it's a crab) set two notches down from top, but still not as smooth as a V8 should be. I'm running 91 octane gas (no ethanol).
Plugs have good tannish colour across all 8, compression test (dry) with WOT gives variation of 5 lbs across all 8 cylinders (150-155 lbs).
I guess I'm brain-storming here, trying to see if I've missed anything. One thing I have noticed is it starts to get a bit ragged when approaching the upper rev limit.
Things I've tried.... different plugs and different heat ranges, every setting on the dissy advance plate, from full advance to full retard, air cleaner on and off, different jets and power valve.
I'm getting quite frustrated.
 
Are the points NOS Ford points? Aftermarket ones can have weak springs and other issues. Was the distributor set up on a machine so you can see at what RPM it starts to get ragged? I have crabs that go to 5500 with no problems. Your bushing must be good to keep the shaft from wobbling also.
 
Just a question here. You state that you are running a Bosch 12v coil with external resistor. I am running the same on two of my flatheads but with no external resistor. Mine have internal resistors and installed them after reading the information that Bubba gives. Perhaps yours is a different coil than I am running. Just a thought. Hope you find the problem.
 
deuce_roadster said:
Are the points NOS Ford points? Aftermarket ones can have weak springs and other issues. Was the distributor set up on a machine so you can see at what RPM it starts to get ragged? I have crabs that go to 5500 with no problems. Your bushing must be good to keep the shaft from wobbling also.
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Yep, crab was rebuilt by Bubbas and tested to 5500.
 
Do put a vacuum gauge on it to see how the gauge reacts. and check to make sure the resistor is necessary for the Bosch coil. Both good suggestions.
 
It's an easy test to figure out what the coil resistance is, I would start there. (Vacuum test is easy as well as far as that goes!)
 
Bassman/NZ said:
It's a black coil, I'll check tomorrow. What should the output of the coil be ideally?
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I am sure it isnt a output problem. With the flatheads compression ratio and fairly low rpm band it might need 10-15000 volts going up a hill wide open throttle.
It becomes a current flow issue high current burns up stuff , and low current or voltage (primary voltage) wont allow the coil to produce enough spark.:eek:
 
Current = Voltage / Resistance. So, if you want a max. of around 4 amps, That would be 4A = 7V / 1.75Ohms. So the resistance needs to be in the 1.5 to 1.75 Ohm range. I believe that 1.5 ohms is want is normally wanted in the system. This needs to be divided between the coil and the ballast resistor. If the coil checks ~1.5 ohms then you wouldn't use a ballast resistor. If it is more than the 1.5 - 1.75 ohm range then the coil has to much resistance for a 6-7 volt system. If it is less, then it needs a ballast resistor to make up the difference.
 
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