Question for Holley carb gurus

[dart_68]

I've been reading on FABO about what is supposed to be the proper way to set the throttle blades on a 4 bbl Holley. I was having problems with it and so I checked my 750 VS. I set both the primary and secondary throttle blades to only show a "square" of the idle slot. However, before this the secondaries blades were almost completely closed and not exposing ANY of the idle slot and the primaries were open so far that the idle slot was almost completely uncovered.

My question for y'all is what problems would the old setup have caused? I know that I did have problems getting it to respond to idle mixture needle changes and the position of the primaries explains that. But what other problems might have been happening?

Thanks!

 

[DrCharles]

Aside from the stinky rich idle, a lean flat spot at tip-in before the mains start, because the transition slot was being used up?

I think on many (if not all) baseplates the secondary t-slot is considerably further up the bore than the primary. Your primary slot should be exposed "square" but no more than .040. The secondaries will likely give you too high an idle speed if they're opened that far.

 

[dano]

What's the carb model number?

 

[MOPAROFFICIAL]

Exposing too much and you are idling off the mains , rich.
Off idle issues occur.

Open them both the same amount, or be able to adjust the secondary closed enough to allow the squaring of the transfer slot with the primary blade.

 

[DrCharles]

Exposing too much and you are idling off the mains , rich.
Off idle issues occur.

Open them both the same amount, or be able to adjust the secondary closed enough to allow the squaring of the transfer slot with the primary blade.

Is there an echo in here?

 

[MOPAROFFICIAL]

Is there an echo in here?

Good advice.
I just read the opener

 

[dart_68]

You're good! Hit it on the nose.

The problem I was having was running pig rich at idle and a tip in bog. I couldn't find a cure for either. Kept fouling the plugs, black smoke out the back...you know the story.

I adjusted the secondaries but now I wonder if it'll idle too high. I only opened them up enough to expose just a square of the transfer slot. I believe the carb model is a 3310. It's a VS 750 cfm.

 

[MOPAROFFICIAL]

You're good! Hit it on the nose.

The problem I was having was running pig rich at idle and a tip in bog. I couldn't find a cure for either. Kept fouling the plugs, black smoke out the back...you know the story.

I adjusted the secondaries but now I wonder if it'll idle too high. I only opened them up enough to expose just a square of the transfer slot. I believe the carb model is a 3310. It's a VS 750 cfm.

What is the idle speed/rpm now?
I mean in park and then idle while in gear/foot brake.
If it is too high..Close the primary some now.

Instead of square on the secondary, you may want less..just barely cracked open even.
You just want to make sure you can get the primary to be a sensitive to the idle mix screws that it will die if you turn them in all the way or too much.

 

[dart_68]

What is the idle speed/rpm now?
I mean in park and then idle while in gear/foot brake.
If it is too high..Close the primary some now.

Instead of square on the secondary, you may want less..just barely cracked open even.
You just want to make sure you can get the primary to be a sensitive to the idle mix screws that it will die if you turn them in all the way or too much.

It's apart at the moment but it was idling in gear around 600 if memory serves me. I'm thinking that I will have to put a secondary position screw in that I can adjust on the car.

 

[Mattax]

secondaries blades were almost completely closed and not exposing ANY of the idle slot

That is correct.

secondary throttle blades to only show a "square" of the idle slot.

And this is not. The secondary t-slots are located further up the bore than the primary t-slots. The main purpose of the secondary idle system is to help when the secondaries are just a little open. They're not supposed to be contributing fuel when driving around town.

I believe the carb model is a 3310.

It will be stamped on the choke tower. There will be the list number - revision. There may also be a date code.

Do this while the carb is off. Take some drill bits or feeler gages and measure how many turns of the idle speed screw it takes to reveal .020 to .040" of the transition slots. Start with the throttles completely closed, screw tip just touching. Write that down some place you can find it when you need it. Then you'll always know how much t-slot is exposed.

I wouldn't go through the trouble of switching the secondary idle screws on a vac secondary unless its really needed.
If you want to crack it a hair more open, do so while the carb is off. It as actually possible to adjust while on the intake - sometimes - but not easy.
Regardless, try another degree or two of timing at the same rpm as before. Say it was at 13* at 600 rpm, then try 15* reduce throttle stop screw to get near 600 rpm. Readjust mix screws by turning them in until the rpms just start to drop, then turn them back richer 1/8 to 1/4 turn. Then check engine in gear. Repeat with 2* more if you want to see if that helps more or hurts.

When my 3310-3 was fairly new, I reduced the throttle position at idle the 'old school' way - drilled holes in the throttle blades. Then had to reduce the IABs (with wire). Its not wrong. I'd do it again in the right circumstances. But in most situations I would start with more initial timing, then maybe crack the secondaries a little, and if yet more air was needed at idle then consider drilling.