I bought a rebuilt 600cfm afb from a local carb shop about 9 months ago. They even istalled it. It ran really well at first but now, it don't run worth a crap. First, I had to change the top gasket because it was sucking air and running too lean. Got that fixed, then I had to change the accelerator pump today due to a chunk taken out of the plastic shaft. After all of that it still don't run right. When I'm really getting on it and shifting into 4th it boggs on me. It also does it when going up hills, unless I slam it into 3rd. I've tried adjusting the air/fuel mixture more times than I want to count. My timing is set right at 12 degrees, have Petronix, and flamethrower, headers, 901 cam, new plugs, wires etc. I don't know what else to do to it. What can make these things go to hell like this? I am stumped!



Somebody Please Help ME!!!!

 

I'm just tossing out idea's but did you recheck the float level lately? could it have moved out of place in the rebuild? did you hook up the vacuum advance to the right port? is the power brake port leaking?

 

Yes, the floats are close, yes the vacuum advance is in the correct port. I haven't found any other leaks, I checked pretty good after I fixed the other gasket.

 

It is also hard to start when it is hot. It seems like it's flooding itself out as it sits. Is there something in there that will let gas flow into the chambers???

 

what kind of fuel pressure do you have when driving and after accelerating through all the gears?

 

I have no clue, why do you ask?

 

If presure is too high it will override the buoyancy of the floats, causing an overfull bowl, flooding the engine. If presure is too low, the engine would obviously starve.

 

I have a new mechanical fuel pump on there, but I have no idea what the pressure is. It should be ok I guess. I took the carb off yesterday and gave the fuel bowls and jets a good shot of carb cleaner, but it didn't seem to make any difference.

 

First off, the Edelbrocks are easy to diagnose when they flood because they are designed such that fuel will come spilling out all over your intake manifold in a flood condition. So, as you have not said anything about a river of gas, I'm sure your floats and pump are okay. Since you can get your carb to behave by downshifting it sounds like to me that there must be a nozzle that is partially plugged so that the low air velocity that is present at the lower RPMs isn't pulling fuel like it should. I checked the Edelbrock website and this sounds like your problem (for whatever reason the picture didn't reproduce):


Secondary Auxiliary System
During the initial stages of Secondary Operation, the air flow rate through the secondaries is very low. Accordingly, there is not enough pressure drop (suction) at the Secondary Nozzle to induce fuel flow. In order to prevent a lean A/F condition that would be experienced by the driver as a "bog" or "flat spot" on secondary opening, it is necessary to add fuel by an auxiliary means during the time the secondary is in the transient phase.

This is accomplished by placing a small Discharge Nozzle (2) at a point just under the Air Valve (1). The air flow past the edge of the Air Valve creates sufficient pressure drop to pull fuel out of the Auxiliary System. The fuel must first pass through the Secondary Main Jet (3) to the Secondary Well; it is then drawn through the Auxiliary Fuel Tube (4) and exits at the Discharge Nozzle (2). There is always an air-bleed, either in the Auxiliary Fuel Tube (near the top), or as a separate brass restriction bushing (shown).

The flow of fuel in the Auxiliary System is enough to prevent a lean transient on Secondary opening. As the Air Valve is opened further by increasing air flow, the fuel flow through this system decreases. Correspondingly, the fuel flow in the Secondary Main System increases, providing a near constant A/F Ratio.


It sounds like the "small Discharge Nozzle" in your carb might have become partially plugged or your air valve has a problem.

Now, for the hard start when hot condition. I have the same problem with my Edelbrock. With mine, if I restart right away, no problem. If the truck sits for a few minutes, hard to start and doesn't want to idle. Haven't solved it yet but suspect that it may be a vapor locking issue.