78 351w idles rough

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Apr 23, 2014 | 09:40 PM

theseeker

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78 351w idles rough

this is a 78 e150 with a 351w it idles rough and misses up to about 1200 rpms maybe 1500 I'm guessing at it. my first guess was bad gas so I replaced fuel and filters not that . so I replaced all wires plugs and cap all the plugs looked real good except for one. and the timing is good. and the fuel pressure is to. the old van drives out good has plenty of power, just real rough idle but it dose idle.it sounds like its only hitting on 3 or 4 cylinders. and I have checked for vacuum leaks. oh yeah 99% for the time it will start rite up with a flick of the switch and not even touching the gas,but if it don't after turning over a few times it will backfire out the exhaust. and it seems to do it as soon as I let off the key !!?!?!!?!
Thanks in advance for any help

Apr 23, 2014 | 11:13 PM

Jklnhyd

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Joined: Sep 2013

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From: Pasadena, Ca

Sounds like your carb needs attention. You may need to check your compression. Is your air filter dirty?

You replaced the plugs?

It may not be "one thing" gonna fix this for you.

Apr 24, 2014 | 10:29 AM

theseeker

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it .could be the carb,but i have checked it out .I do know it's not the power valve. and the compression is good.
1.replaced fuel and fuel filters one inline and the one on the carb
2.replaced plug wires
3.replaced spark plugs
4.replaced cap and rotor
5.set timing and checked the firing order it is in order
6.checked for vacuum leaks
7.checked all wires and connection on the ignition
this problem came out of know where. we drive this old van on a 400 mile round trip at lest once a month. I filled it up with gas on our way back home it ran fine and idled fine. monday am I was going to move it and it started this.