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New
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979 Posts
Discussion Starter #1
I give up trying to solve this myself. After installing new heads (AFRs), and being really pleased with the HP increase, I discovered that once-in-a-while, when putting a heavy foot on the accelerator, it will miss and sputter at about 4500 rpm. If I back off of the throttle a bit and then feather it back up to the problem rpm it will resume normal operation and go to red line like a scalded ape. Because it happens on an irregular basis, I was suspect that the improved airflow rate was causing a lean condition until the electric fuel pump (back by the fuel tank) could catch up with demand. (Demon carb with a return fuel system.) Well, I installed a much stronger fuel pump and can now set the fuel pressure to 6 psi at the carb (the prior pump pressure was internally regulated and the flow was insufficient to be able to restrict it at the pressure regulator).

Problem - it still happens. So - I'm off to once again verify the float level and will regap the 3924 plugs (opening them up a bit to .045) but I really don't think that will solve the issue.

BTW - I'm using a Crane ignition with a Malory distributor.

You folks got any other suggestions.

Thanks,

Darrel
 

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Crisisrider
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164 Posts
I had a Lincoln Mark8 that had a similar problem under load at mid RPM range and it was a plug wire..Just a thought.
 

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Speed-crazed and Confused
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2,357 Posts
I had the exact same problem last year. A new set of autolites and all is good.
 

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Supporting Vendor & Admin
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8,396 Posts
I'd gap the plugs to .032" as it seems to happen at the torque peak where the cylinder pressure at its greatest and the ignition load is the highest. Check the cap and rotor, plug wires and coil.
 

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New
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979 Posts
Discussion Starter #6
OK folks. This afternoon will be a full inspection of the high voltage electrical and re-gapping the plugs to 0.032. I believe I have a new cap and rotor and they will go on. (If I don't, it is because I've already used them in attempting to solve this issue.)

Thanks for your comments. If you have time - can someone explain why, if it is an electrical issue, what is happening that makes it irregular in occurrence. (Unless it is fouled plugs or a fouled plug, what explanation is there?)

The frustration this afternoon is that I won't be able to test any changes until the snow clears.

R, Darrel
 

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979 Posts
Discussion Starter #7
Well, don't ya just know

Found something wrong with the distributor cap. (Missing center conductor.) Hopefully - this is the culprit.

 

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East Coast Speed Machines
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2,919 Posts
Got that T-Shirt!!! I spent months and $$$$ changing stuff out until I found that! Do yourself a favor and check the resistance on all the plug wires make sure you don't have a one that has excessive resistance. I found 1 bad wire (high resistance) and one open (only when I moved it around) when I found my button eroded. Make sure you move them around as you check them.
 

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Registered
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415 Posts
Start it in the dark and see if you see any sparks. We found a bad wire sparking over onto the headers, o just Rick new this trick
 

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Discussion Starter #11
Thanks gents. As soon as the snow and mud clear I'm off for a test drive and then, if needed, the other recommended tests.
 

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East Coast Speed Machines
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2,919 Posts
just know that I went though 2 caps and one rotor and couldn't understand why I was getting build up under the cap....my guess bad plug wires all along....
 
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