Holley 650, vacuum secondaries, just rebuilt. 400, Edelbrock intake, RV Cam, Auto, blah blah blah...

I've been tweaking with the carb for the past few days, floats are good, PV is good and gasket is seated properly, fuel pump pushing 6-7, vacuum is a steady 18 (no leaks!), BARELY drops when in gear, idle screw is all the way out, timing at 8 degrees, choke plate all the way open.

Been blowing black smoke until today, turned the mixture screws in all the way in, and it struggled to keep running with the throttle part way down. Pulled the PV, and checked it (sucked on it) and it is good. PV Saver installed, checked the last PV and it's still good too (so that wasn't my original problem). Slapped it back together and messed with it more. I think it just kept barely going and the vacuum got low enough to open the PV to barely keep it going. Now I messed with it a bit and it dies when the screws are all the way in. The RPMs DO NOT drop at all when I turn the screws in. It either runs rich (black smoke) or dies (screws in), no middle ground.

The problem I'm currently having is that it backfires when I slam on the throttle (acts like it's going to bog for a minute, then backfires, then revs). If I advance the timing WAY in advance, it doesn't do it at all, but then the RPMs are WAY too high at idle. Recurved the dizzy with the Crane Cams kit. Currently running the double yellow springs, and have tried turning the vacuum advance out further, but still backfires every time if I keep it in the 650-750 RPM idle range.

I've been reading like a madman since Sat on all the causes. Checked and double checked everything listed on here, the Holley site, FordMuscle.com, etc... What I can figure is the secondaries kick in and it's still getting too much (or too little) fuel, or the timing is just royally messed from the recurving.

Please! Somebody give me a fresh idea of what I could try next before I just torch my truck!

 

Its sound like the timing to me.

 

If you disable the EGR, you need to recurve the dizzy to slow down the centrifigal advance to prevent pinging at low speed.

What effect do the double yellow springs have on the timing?

Holleys have a known problen where the secondaries open too soon. There is a fix for that, but I don't know what it is.

 

According to the paper that came with the dizzy kit, The yellow-yellow combo puts full engine advance RPM at 3,100 rpm. I've had no problems with pinging so far...

I'm really starting to aim towards the carb. When I hit the throttle about half way, the truck bogs down and either dies or backfires. If I slowly work my way up to the higher rpms, it doesn't seem to do it. No matter where I set the timing, with or without the vac advance on it, it does this the same way, at the same spot.
I'm thinking about backing off on the accelerator pump a bit, see if that helps. If that doesn't fix it, I'll try disconnecting the secondaries and see if it makes a difference...

 

Good idea. If the secondaries open when the RPM is too low, then the vacuum drops and neither the primaries nor secondaries supply fuel.

 

Just disconnected the secondaries (at the rod going to the secondary diaphram) with no change at all. Also adjusted the accelerator pump out (it was pushed pretty far in) with no change.

Don't even know where to go from here. Like I said before, if I slowly work my way up in rpms, it's fine until revved WAY high, then I hear some small backfiring. But when I snap the throttle, it sends out flaming ***** and the throttle plate looks wet with fuel...

 

Does this happen under load only, or does it happen when you rev it in neutral?

 

Revving in neutral. Does it under load too.

 

Have you double checked the firing order?

 

I know the firing order is good. Motor starts right up and runs smooth. I actually never disconnected the cap or wires from each other, and the only time the wires came off at the plugs was installing the intake.

Another site suggested I could be a tooth off, but when set to TDC, the rotor is right where it should be, and the timing set is under 4k miles, and has worked fine with the last intake/carb setup.

 

I am throwing my .02 in the timeing pile. Next, the carb for some reason is dumping fuel in---badly! If the carb was running good before, then I have to think it is something to do with the power valve or the accelerator pump circuit. Somewhere, it is pulling in extra fuel.

I rebuilt a 306 some years ago that had a 750 4010/4011 (cant recall which was the square bore). It did the same thing. you could almost see droplets of fuel pulsing back over the throttle plates at idle. Be careful! that much extra fuel will seriously dilute the oil (especially on a new motor at break-in) Because of the extra stress on the front cam bearing, it will fail on a new motor---mine did. My problem was a power valve spring too light and the actual "jets" in the power valve circuit were way too big. This may not be your problem, but if not timing or a crossed plug wire, it could be too much fuel.

Are you using a duraspark ignition? A bad module is also possible.

LOL

 

Check the float level. Also look for fuel drops in the venturis at idle. Excessive fuel pump pressure can cause flooding,

 

Float level has been checked and rechecked, fuel pressure is regulated down to 5 now. The carb was running on my roommate's truck, but not well and it leaked all over the place. I rebuilt it when he put an Edelbrock on his truck. I've checked and rechecked, and my power valve are good (I replaced it thinking it was the problem, that's before I read you can just suck on them to make sure the diaphragm works, so now I have a spare).

I'll look down it for excessive fuel at idle (not too interested looking down the carb for all the fireballs I've seen, but should be okay idling)

 

Got out there, messed with the timing a fuel pressure, and still no change... Took a vid of what it's doing (you need Quicktime to play it) Doesn't want to backfire as much right now, but still bogs down and kills the motor.
http://s69.photobucket.com/albums/i4...1408_1715a.flv
Not the most exciting vid, and the sound sucks since I took it with my phone.
Then I ran out of gas...

Also checked the plug wires, and they're all where they should be. Looked down the carb, and could see no fuel on the plates or anything. Not about to look down there and hit the throttle

 

After it has run a little, shut it off, then look into the carb and open the throttle like you did in the video.