Very good ideas to check into so far. I worked for Holley for 13 yrs. Email in profile if you have any questions.

They've been out for a while and they're sound.

I had 650 dbl-pumper w/ mech. secondaries in my '67 Mustang. I had a similar issue to yours but mine was a combination of a rotted gasket in the back bowl and an idle that got completely out of wack(from me messing around with fuel mixture trying to figure out the stalling).

If you don't think it's the pump and you've already rebuilt the carb, and double-checked it, I'd have to agree that you'd have to look again for vacuum leaks.

Barring that, you have to look at air flow. Check your throttle plates for proper opening when the secondaries engage. If your carb is leaning out the engine prematurely that could be causing it. Assuming you're good with fuel mixture and idle set.

Other bogging issues could be head-related but I think that'd present other issues (smoke, milky oil).

So then airflow in the head. Assuming the head is properly sized for the engine (350?) and your application: daily-driver vs street racing vs track w/appropriate cam. I'd dbl-check your valve lash and adjust accordingly.

Crate engines aren't like factory engines, they need a whole lot more care and feeding. Especially if it's been sitting for a long time and you've been fighting this for a long time.

so what is the best way to check for vac leaks?

quote:

Originally posted by thumperfbc:
so what is the best way to check for vac leaks?

If you take the nozzle and orifice out of a propane torch, hook a hose to it and run the end of the hose around the base of the carb, intake gaskets etc. If the engine speed varies it indicates a vacuum leak. You can also use WD40 but it is quite flammable so be careful.

I could not tell you how many times I've chased stuff like this only to have it be an electrical issue on Gen 1 SBC and BBC.

One cheap thing to check is with the engine running at night in a dark area with the hood up look over the spark plug wires. If they are bad or leaking you will see blue sparks or voltage jumping in bad areas or even following the wires length wise on the outside.

Has the timming been check with a good timing light the correct way with vacuum advance plugged? Is vacuum advance working? Is vacuum advance connected to ported or non ported vacuum? Is the mechanical advance in the HEI working? and not froze up or broken springs? Have you checked to see if HEI is really getting 12 volts?

I would lean toward the fuel pump. You can probably add an electric one pretty cheaply.

I would add to Jellys advice by saying brake torque the car while someone else looks for sparks. You may find it occurs at a certain RPM.

As far as finding vacuum leaks I generally spray any suspected area with carb clean and liston for an RPM increase.

Jim

Replace the power valve to rule it out. They are another variable item. You select one based on the idle vacuum in gear for your particular engine. Abackfire through the carb can ruin it.

One pain is a speck of dirt in the wrong place can be the cause as well.

quote:

Originally posted by Jelly:

Is the mechanical advance in the HEI working? and not froze up or broken springs?

This is a common problem with the HEI distributor.

Some really good areas to investigate given. While messing with the carb, pay attention to the jets and nozzle passages. Ethanol allowed to sit long enough can clog them, and won't always dissolve with just carb cleaner. If you discover such a condition, replacement is easy; poking a tag wire through will also help.

Just a WAG, but I've run into this on motorcycle carbs.

quote:

Originally posted by egregore:

quote:

Originally posted by Jelly:

Is the mechanical advance in the HEI working? and not froze up or broken springs?

This is a common problem with the HEI distributor.

Check the wires to the HEI module too, movement from the vacuum advance breaks them over time.

quote:

Originally posted by dynorat:

quote:

Originally posted by egregore:

quote:

Originally posted by Jelly:

Is the mechanical advance in the HEI working? and not froze up or broken springs?

This is a common problem with the HEI distributor.

Check the wires to the HEI module too, movement from the vacuum advance breaks them over time.

This!