My 85 F250 w/ 460 and stock Holley...

Finally got her running yesterday, and now we are down to diagnosing a severe misfire. At idle it sounds like its got a high lift cam and I had to turn the idle screw all the way in to get her to idle without dying but the wider open the throttle is the more it smooths out.

I have already replaced the cap rotor plugs etc...

Yesterday while test running in the driveway (still not driveable, gonna be fixing the brakes today) it did smooth out and idle perfectly for about thirty seconds, then it ran out of gas. I put more gas in it and the misfiring was back.

I was gonna take a video for you guys but I couldn't figure out how to put my phone's cam in video mode. It was smoking, a mix of black and white which increased with more throttle until WOT, then the smoke decreased.

I'm not sure what else to look at since I already did the basic tune up stuff? Sorry if this is a stupid thread but I'm just not too familiar with these old carb'd engines...used to working on imports in which case I'd be plugging in a computer and diagnosing that way.

Ideas?

 

Does your 4180 have a blown powervalve?
If you take the air cleaner off is there fuel dribbling out of the primary boosters?

 

Powervalve?
I couldnt find any fuel leaks, already looked for that.

 

Yes.
Earlier Holley's are notorious for this.
Starting in 1991 they had a little ball to protect against backfires.

If it doesn't die right away with the idle mixture screws all the way in, then it's blown.
Does it pop on trailing throttle?
Can you even drive it yet?

 

My first thought was also the power valve, but backing out the mixture screws that much would indicate a lean condition/vacuum leak/low float levels/ clogged fuel filter, but the black smoke contradicts that......weird.

 

Screws in.
What happens?

 

when i said idle screw i was referring to the one that pushes on the throttle linkage to make it idle higher...now i will need a quick how to on adjusting idle mixture screws where are they etc...sorry if it seems like im being retarded i just dont know anything about carbs..i did notice it pop/backfire a couple times while I had my foot about half into the throttle maybe a little less

 

Your powervalve is blown.
Use a 3-1346 rebuild kit.

Or get a generic 4v 600 cfm carb like I have.

 

I figured out what you were talking about with idle mixture screws...put em most of the way in and she ran ALOT better. So itll be getting a diff carb to put on it.