I've got an 86 f250 with a 460. The PO put an Edlebrock performer intake and a newer Holley carb. I can't make out which Holley but its a 4bbl. When I got it, the distributor was off one tooth and the carb was all messed up. It was shooting flames from the tailpipe.

My buddy has fixed the distributor, reset the timing to 10 degrees and tuned the carb to set the idle properly. We found that a vacuum hose was missinfg to advance the spark and have replace that.

We're both scratching our heads on the next problem. The engine sounds good at idle and pulls strong up to 2000-2200 RPM but then it falls flat. My only guess is that the secondaries aren't kicking in but I'm no mechanic.

I'm leaning toward replacing the carb with an Edlebrock performer 600 or 750 cfm but don't know if that would help. I've read a lot of people ditch a Holley setup on the 460. Any thoughts or ideas would be great!

 

Is the advance on the dizzy working? You should get advance into the 30 degree range when you rev the engine. Check with the vac conected and disconected. How is the exhaust? Clogged cat?

 

What the number on the choke plate on the Holley.

For example...3310-2 is a Holley 750 CFM 4 Barrel

 

Vacuum or mechanical secondaries? You said you had a vacuum line missing to the advance canister, could you something else leaking vacuum keeping vacuum secondaries from working properly? It sounds like it's probably a fuel restriction to me.

I have an Edelbrock 1406 600 CFM carb on my 460. Vacuum secondaries, electric choke. It's just about dummy proof...

 

I didn't have a chance to work on it this weekend since its at my buddy's shop. I did do A lot of reading. I'm going to start by checking out the fuel sending unit with a fuel pressure gauge. If that checks out then I'll go under to see if the exhaust is a problem, but I think because its GVWR is 8600 that it was excluded from the Cat requirements. I'll probably replace the distributor cap regardless just to eliminate that.

Last on the list will be the carb. As I mentioned we have that tuned and it doesn't seem to have a problem with the power valve. Although I would prefer to change it to an Edlebrock 1406 or 1411.

One thing I did realize as I was reading is that the emissions "stuff" has been removed. I'm hoping that they knew how to do that properly or that could be a can of worms.

 

Well that's interesting. There should have been a line off of the air pump (which I guess is now gone) that goes to the back of the engine. I believe that it either needs to be hooked to the air pump or be plugged up. With that line just disconnected, it'll run rich. I know of one case where it even made a straight piped 460 throw flames about 3 feet ('86 like yours) if you were on the gas heavy then let off.

Hopefully you can get a good look at it soon. Good luck!

 

So I had a few minutes between rain storms to mess with it a little. Here's what I've learned

1. No cats so that's ruled out.
2. The carb is a Holley 80457-8 600cfm with electric choke on an Edlebrock Performer 460.
3. Emissions are all removed.
4. The distributor cap and plug wires are in good shape.

With base timing set to 10* and the carb tuned the motor stumbles and shakes still at 2K.

I'm going to get a timing light on it after the next storm to see what's happening with the timing at 2K. I have a feeling that its the ignition system. Just hoping the timing isn't the culpurate.

 

The air pump only adds air to the exhaust. There is no way it will change the mixture. The flames are from a high vacuum sucking fuel when the throttle is closed fast.

 

Does anyone know if there's a way to test an ignition module without replacing it?