Plug gap after elec ignition mod
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Lead Driver
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From: Other side of the sunrise
Plug gap after elec ignition mod
Hey folks, I have a '74 F250 4x4 that is powered by a '68 460 Lincoln engine. Years ago I slipped an electronic ignition distributer into it and parked the old points ignition in the garage. There were quite a few modifications going on at the same time so it's hard to diagnose the less than perfect running without throwing a ton of money into it. So that's why I'm reaching out to you all in my mental, non-wrenching process of elimination. This truck has been sitting for a long time, only used for hauling firewood once per year so I lived with the way it ran, which wasn't unacceptable, but I think it should be putting out a little more under peddle. Here's the question: When I added the electronic ignition, should the plug gap still be .035 or is there a different gap I should be using? I have new plugs and wires ready to go in. Thanks in advance.
Cargo Master
Joined: Oct 2020
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There's no problem with running a .035 gap with electronic ignition but with that said it can typically handle a gap of .045 to .075 with no trouble. Will it run better with a wider gap? Maybe if you're running a mixture that's right at the point of lean misfire.
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Lead Driver
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Interesting. So it seems to sound (to my untrained ear) like the engine is misfiring or floating at higher RPMs as I work through the gears (4 speed). Might this be the "lean misfire" you're referring to? Would you suggest that I try a wider gap at this tune up to see if this resolves the symptom? As far as the mixture, I set an Edlebrock Carb on it when I did the engine swap to the 460. I seem to remember it was a 750 CFM, which Summit said was the carb recommended for the 460, but it seems like it runs lean to me, like at higher RPMs it's starving for fuel. Like I said, however, that's my untrained ear. Thoughts?
Cargo Master
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Edelbrock has two versions of most of their AFB style carburetors; a regular and an emissions calibration. The ones that are emissions calibrated are far too lean for best torque especially when you are running on modern fuels. You certainly should try opening up the plug gaps, try going up to about .060 and see if it's better or worse.
One time a few years ago I had a 289 that I built for a customer running on my dyno breaking in the cam by running under a 20 horsepower load at about 3000rpm. With the engine sitting there running it sounded find but just lightly choking the engine made it pick up about 8lbs/ft of torque. Then when I would take my hand away I could tell that it was nosing over and almost surging. I think that I went up about 12% or so and the engine ran great just as good as it would with a similar Holley carburetor even though the AFB is smaller because they are not rated the same as a Holley.
One time a few years ago I had a 289 that I built for a customer running on my dyno breaking in the cam by running under a 20 horsepower load at about 3000rpm. With the engine sitting there running it sounded find but just lightly choking the engine made it pick up about 8lbs/ft of torque. Then when I would take my hand away I could tell that it was nosing over and almost surging. I think that I went up about 12% or so and the engine ran great just as good as it would with a similar Holley carburetor even though the AFB is smaller because they are not rated the same as a Holley.
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