400m Lopes when hot

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Jul 12, 2001 | 03:16 PM

Rediranch

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400m Lopes when hot

Hi and thx in advance.

I have a 1978 F150 4x4 Heavy Half ton Extended cab with a 400m in it (rebuilt, 31k miles). I just bought it 2k miles ago. The emissions are intact and working (passed just fine).

When the engine gets hot, it lopes. Runs great when cold, but doesnt take long to start loping. Yes, I'm running the AC (live in Phx!), but even does it when AC isn't running.

I've checked all the vacume lines, and can't find one not attached, but figured that if one was off, it'd run bad cold, too.

Any ideas?

Jul 12, 2001 | 03:58 PM

beartracks

Lead Driver

Joined: Nov 2000

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From: Albuquerque

400m Lopes when hot

Might be an EGR leakage problem.Could be the EGR plate under the carb leaking internally, especially if it's made of aluminucm.

1977 Ford F-100
400m/c6/4:11/Gear Vender O.D.
Crane hydralic roller, forged, ported polished,Deamon,Edlebrock, yada, yada, yada
280,000 miles
Stock on the outside
modified/rebuilt everything

Jul 12, 2001 | 11:10 PM

Franklin2

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From: Virginia

400m Lopes when hot

If it has a steady lope, I would suspect a dead cylinder. While it is running, pull each sparkplug wire off and put it back on. Each wire should make a difference in the way the engine runs. If one wire doesn't make a difference, that is your dead cylinder. If the engine doesn't have a steady lope, but more of a random shake, I would suspect egr, vacuum leak, idle adjustment, etc.

Jul 15, 2001 | 01:36 PM

fozzy

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From: New England

400m Lopes when hot

retork the intake bolts. spray some carb cleaner around intake, carb, if engine idles up correctly while you are spraying carb cleaner, then you have a leaking intake gasket, if it does this around carb, well....you get the idea

https://www.ford-trucks.com/dcforum/User_files/3a9df0394b631ce6.gif

77'FORD F150 XLT 400

Aug 22, 2001 | 11:23 AM

Shoebox

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400m Lopes when hot

I assume you have found solution by now. However, I have found solution to similar problem on 351W with Motorcraft 2150 carb. There is an enrichment valve under bottom of float bowl, which, if leaking due to deteriorated diaphram, will allow fuel to be sucked into bottom of carb barrels. It probably takes buying a carb kit to get the valve.

Aug 24, 2001 | 06:04 AM

bigricker

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400m Lopes when hot

I just rebuilt the same carb last night using the kit and it does not come with the valve you mentioned. just seal and rubber parts and stuff. sorry, if that is it then, new carb?

Aug 24, 2001 | 02:14 PM

Franklin2

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From: Virginia

400m Lopes when hot

That valve is commonly known as a "power valve". If the kit didn't have one, it must have been a cheap kit. You can get these seperate at the parts counter.