Hey guys here again....

1985 F150 302 4bbl holley 600

Was running fine several months after a new carb was installed, yesterday... I did a smaller burnout from about 6mph at about half peddle. instantly after the burn out the engine began acting like it was going to die as I stopped at stop signs. Leaving a stop sign I would give it gas to take off and it would act like it was going to die again then pick back up and did fine.

After getting it home I noticed the idol was much higher and it still starts cold well but I have to start it several times before it will keep running. Once it is running, the idol is still high at OP temps and it sounds like the carb is sucking more air than normal...but that might be just because I took the cover and filter off.. so the air sucking could not even be a part of the problem.

Other things I noticed..

Once I get it up to around 55mph, it seems to be running smooth and hase it same pick up power, but as soon as I start slowing down it begins to act starved again.

when moving at 55, if I let off the gas, then back on it, it jerks kinds hard just before picking back up and running smooth again.

Any ideas?

So far I have been looking for a vacuum leak, but have not found any.
While it was running I did spray a bit of carb cleaner around the carb but didnt notice any more surging.

The idol sounds good at OP temps with the exception of high idol.

When I get it started where it will run by itself, I slightly rev the gas and it revs but is very slow to come out of the rev. Before I would rev it, it would rev and right back down to idol, now I rev it, and it is slower to get back to the idol speed which is still high at

 

WAG, maybe the timing chain jumped on the timing set? Is it a high mileage engine?

 

Or, perhaps the distributor was a little loose and has rotated just enough to disturb the timing?

Make sure the secondary plate is fully closing... Sometimes, when not used regularly, a little varnish will build up on the shaft and the secondary plate will stick open, disturbing the low speed air ratio.

 

Thanks guys, I will check this out right now and get back to you. I have not checked none of these ideas yet...so....But the timing chain is new, was put on about 6 months ago when the new carb was installed, but still worth looking into. and yes, the engine has around 80k on it

 

Hm.. should not be a factor if timing set is new.

 

OK, checked the timing, is right on, after warm up, engine sounds great with the exception of the high idol and surging I get when I rev it.
Idol is around 1200 at OP temp, when I put it into reverse, idol jumps down to around 300 and the engine dies unless I bump the gas a hair when putting it into gear.

The dizzy was tight, I marked it and loosened it enough to turn it while it was running and turned it until the idol sounded close, but the surging was still present and it still died when put into gear.

I also checked the secondarys and they were closed like they should be.

Any other possibility's

 

Did it happen to backfire? I wonder if the power valve is blown.

 

No, it has not backfired at all, I keep expecting it to but not even once

 

Im wondering if something got sucked into the carb and clogged one of its many tiny air and fuel holes? is that possible?

 

Yes, but that wouldn't make it idle higher. It is more likely that the linkage changed and the fast idle cam has come in or the linkage is preventing the carb from going back against the idle stop.

 

OK, so would that by any chance make the engine really slow about coming back to idle speed after revving it?

 

Yep. Something is probably holding the throttle open. Pull the air cleaner and look to see if the linkage is allowing the throttle to hit the throttle stop.

 

Both the front and back plates look as if they are closed until I push the throttle. I did notice this time that the vacuum line going from the break booster to the engine just behind the carb, when I spray carb cleaner in that direction, it revs up a little....could this be where the problem is?

 

Could be that you are getting a lot of air into the system via the brake booster hose.

 

Check for vacuum leaks.
Aftermarket carb, there may be a cap missing in the back, or one of those rubber caps has gotten brittle.