Leaning out at Idle - Vintage Mustang Forums
 
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post #1 of 5 (permalink) Old 11-14-2017, 09:40 AM Thread Starter
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Leaning out at Idle

So my car runs great from a performance standpoint. However when I sit for long periods of time then it slowly leans out. Last night I was stopped at a railroad crossing and when I stop I'm at 13 to 13.5 AFR at 180 degrees engine temp. Then it slowly starts to creep up to 14 AFR and my engine temp climbs as well. When it starts pulsing between 14.5-15 AFR the engine starts stumbling and running rough like it is missing but does not die. The AFR can get erratic at this point. The engine temp stays at 195 which is the thermostat opening temperature. I have the same problem in the summer but it tends to happen sooner. When I was sitting at the crossing last night I was idling for nearly ten minutes but only started stumbling for the last minute or two. I'm stumped, any idea what is wrong?

david

69 Winter Blue 302 Fastback w/ Original Paint

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post #2 of 5 (permalink) Old 11-14-2017, 10:05 AM
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Could you be getting into a vapor lock situation as underhood temps climb and fuel is not moving as much at idle?

You might be able to test this in your driveway with an inexpensive infrared thermometer.

Also - do you have an electric fan or mechanical fan?
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post #3 of 5 (permalink) Old 11-14-2017, 10:20 AM Thread Starter
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Vapor lock - that could be what is happening especially since my fuel line is larger. I have a mechanical flex fan with a shroud and an open air element like they used on the Hi-Pos. The fuel pump is a mechanical Edelbrock unit with 3/8" fuel line. How would I test for vapor lock with an infrared thermometer? Do I check the temperature of the fuel line itself?

david

69 Winter Blue 302 Fastback w/ Original Paint

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post #4 of 5 (permalink) Old 11-14-2017, 10:30 AM
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I would measure the temp of the fuel bowls.

In my case, I installed and electric fan and my underhood temps went up due to fan not coming on - I had it set at 200 degrees.

My fuel line was also routed way to close to the intake manifold and picked up a bunch of heat from there.

Do you have a carb spacer? Those will help.
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post #5 of 5 (permalink) Old 11-14-2017, 11:49 AM Thread Starter
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I do have a 1" carb spacer. My fuel line is not very close to the intake but it does pass behind the distributor instead of in front of it.

david

69 Winter Blue 302 Fastback w/ Original Paint

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