spark plug gap

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Apr 11, 2004 | 09:10 PM

jitter1976

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spark plug gap

i have a 1978 F150 4x4 with a 351w new plugs new wires new distributor and rotor but the place that put them on said they had to reset the gap but now it idles perfect but cuts out and backfires at about 2000 rpms but only when in gear and moving it does not do that when sitting still at 2000 rpm could they have gapped the plugs wrong any help would be greatly appreciated oh and weve checked the timing and seems fine

Apr 11, 2004 | 10:12 PM

Mil1ion

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I bet that is a 351M not a Windsor.

The gap is probably .044"

You can ask this in the 351 engine series forum as it is not 73-79 Truck specific

Apr 11, 2004 | 11:34 PM

Matts72

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From: Montana Territory

yeah, 302, 351W,C,M, 400, 429, 460 all have a .044" gap

Apr 12, 2004 | 09:42 AM

beartracks

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From: Albuquerque

Sounds like they messed up a plug or wire.

Apr 12, 2004 | 03:34 PM

bobs75f-250

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From: Butler, PA

What's the gap for a 360? Is it .038"? I'm having a very similar problem.

Apr 12, 2004 | 05:27 PM

corv_66

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From: Northern California

Have you checked the vacuum advance? Also, does it backfire when you step on the throttle at all rpms, or does it only do it at 2000 rpm? Because it sounds like a vacuum or carberation problem.