Desperate Mechanics help needed
Senior User
Joined: Jan 2005
Posts: 143
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one question for ya.....Has the engine ever backfired up through the carb? If it has, that could be the problem. With Holley carbs it only takes one good backfire to blow out the power valve. Spectre sells a part that is very easy to install calle the power valvew saver. Replace the power valve. I had a 1978 f-150 4x4 that kept blowin out power valves. The truck would run great for a lil while then once it's warmed up and driving down the road it would start loading up and spittin and sputtering. The only thing I could do to keep it running is to feather the gas and try to power out of it. I changed out my carb for an Edelbrook AFB (identical to the Carter AFB) then I figured out what caused my backfires and it ran great.
Senior User
Joined: Dec 2004
Posts: 236
Likes: 0
From: Southwest Montana
This is not by chance have a cab mounted tank in it doesit? If so look in the tank for a disc seal out of a fuel addative bottle. they float in under the fuel sucker pipe and plug it up. when the engine dies the vacume goes away and the disc then floats away till next time. This happened to my sons truck and was exactly the same symptoms.
Ken
Ken
Senior User
Joined: Aug 2005
Posts: 424
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From: southern Indiana
my 78 with a 351 m did the same thing at 55-60mph I thought my tranny was going out but ended up being one of 2 things I found a vacume leak at the egr spacer,and I repaced my ignition module box.So one of the two was my problem.Start it and spray carb cleaner or starting fluid around the base of the carb and intake And listen for pickup of rpm.by the way do this on a cold engine.Sometimes heat will cause the ignition module or coil to act erratic.
Tim
Tim
Senior User
Joined: Aug 2005
Posts: 424
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From: southern Indiana
Have you done a fuel flow test to completly rule that out? 5 easy steps(1) Remove the fuel line from the carb.(2) Put it into a quart jar,(3) disconnect the wiring connector going to the coil.(4) crank the engine over.(5)It should take X amount of seconds reach a pint in the jar,or to fill the jar.Can someone help me fill in the x and tell if its per quart or pint its been a while I forget
Tim
Tim
Thread Starter
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Freshman User
Joined: Dec 2005
Posts: 38
Likes: 0
It's the fuel, when the truck shut off I got out and pumped the throttle and dribbles of fuel came out, I pumped it a couple of more times and it sqiurted, so I'm thinking maybe I need an electric fuel pump. Or could I possibly raise the float level to make it not run out of fuel? Also I shortened the fuel lines and took out my fram fuel filter since the carb has filters on it already, still I need help on keeping her running while going down the road, above 25mph she starts to starve for fuel, any ideas?
Last edited by 81broncoguy; Dec 20, 2005 at 03:31 PM.
Posting Guru
Joined: Aug 2000
Posts: 2,416
Likes: 4
From: PacNW
I'd start by replacing the existing mechanical fuel pump with a new one. Definitely check the float levels but raising them to overcome a fuel pressure problem isn't going to help much.
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From: western montana
I knew you didn't have aux tanks...eerrr... but the story is about a clogged fuel system whether switch or line or tank. I would remove the gas cap- unzip the fuel line going from the tank to the pump and, with compressed air, blow back towards the tank. Your prob is soooo similar to mine and given the age of the vehicle i would say that your not geeting a clean path from your tank- probably corrosion in the tank- if so- when you blow it out with, say 50-60lbs of pressure, your motor should run fine until it clogs again and then you will know to replace the tank- I'd put big time $$$ on this... or you have a block somewhere else and..assume you've checked all the filters to include the on in the carb if equipped.
Thread Starter
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Freshman User
Joined: Dec 2005
Posts: 38
Likes: 0
Thanks for all the help guys, I think I blew the power vavle in my holley, because I've backfired through the carb several times so I'll have to replace and I plan on getting a power valve saver.
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