Idle Question
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Trailering
Joined: Mar 2025
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Idle Question
Hi ya’ll - idle question on a 1971 F100 360 with a Motocraft 2100 carb. We replaced distributor, wires and plugs and now have an idle question. It won’t idle when hot. Runs great at start up but once engine warms it won’t idle. Suggestions on where to start?
Fleet Mechanic
Joined: Mar 2013
Posts: 1,662
Likes: 1,063
From: Montana
Typically 8-10* BTDC to start, then I usually add a degree at a time, take for a drive, listen for pinging, if I hear no pinging under light load, partial throttle, I add another degree. Keep doing that until you hear detonation/pinging. Once you find the limit back it off a degree or two.
General idea, have as much advance as the engine will tolerate without pinging. The more advance you can add, the better your bottom end/off the line performance will be.
After timing is set, you can then fine tune the carb.
Are you sure the choke is opening fully when warm?
Is the curb idle set to give you about 700 rpm give or take 25 points when truck is fully warmed up and choke is completely disengaged?
General idea, have as much advance as the engine will tolerate without pinging. The more advance you can add, the better your bottom end/off the line performance will be.
After timing is set, you can then fine tune the carb.
Are you sure the choke is opening fully when warm?
Is the curb idle set to give you about 700 rpm give or take 25 points when truck is fully warmed up and choke is completely disengaged?
Cargo Master
Joined: Oct 2011
Posts: 2,251
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From: Kenner,La.
The idle metering screws should be 1.5 turns out from lightly seated. Try removing them and with compressed air or carburetor spray cleaner then re set them. Get a vacuum gauge to see how much vacuum the engine has.
As said before get the timing set right. Are you sure the points are set correctly?
As said before get the timing set right. Are you sure the points are set correctly?
Lead Driver
Joined: Jul 2017
Posts: 9,606
Likes: 1,175
From: San Jose, CA
And by “won’t idle“ what exactly do you mean?
Is it just so low that it stalls? Is it rough and chugging?
Something else?
Really rough might indicate that you have a bad plug wire or two. Probably the “or two“ part.
Or it might mean, in spite of your best efforts, you got the plug firing order incorrect.
How did you install the new wires? One at a time, or all at once?
Is it just so low that it stalls? Is it rough and chugging?
Something else?
Really rough might indicate that you have a bad plug wire or two. Probably the “or two“ part.
Or it might mean, in spite of your best efforts, you got the plug firing order incorrect.
How did you install the new wires? One at a time, or all at once?
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Trailering
Joined: Mar 2025
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Been a while since I followed up on this thread. Tuned the carb a bit and advanced the timing as described. Idles great now, runs really well. But we broke the shifter it seems. One problem solved and another one created so back in the garage.
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I also have a 71 360 7bbl. Mine wouldn't hardly start or run. I did put a new carb on but found out the points had been changed over to petronic system. They suggest timing between 12-16 btdc AND the coil needs 12v. After I fixed those 2 items. It now starts, idles, and runs a whole bunch better.
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Trailering
Joined: Mar 2025
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@bangorbob is yours an automatic or 3 on the tree?
we have a 3 speed and something broke over the weekend and truck is stuck in first gear. Not sure where to start on that.
we have a 3 speed and something broke over the weekend and truck is stuck in first gear. Not sure where to start on that.
Banned
Joined: Apr 2025
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I assume, which I hate that word, that the new distributor has electoric points built in. Test you coil to see how much voltage it is receiving. Mine was around 9.2. Not enough for electronic point system. Read on line to see if yours needs a full 12v to the coil. My plug gap also needed to be opened to 42-45.
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