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holley 750 vac issues

Posted By: HOTMOPR

holley 750 vac issues - 01/08/13 02:51 AM

Ive never really dinked around with vacuum secondary carbs much. I just went through one for my 63 413 4 speed. It idles and starts good but has a cruise stumble. When cruising steady throttle at 2000 rpms and I try excellerating slowly it cuts out. If I mash it it goes. Its that mid rpm cruising range that seems to be the problem..
Posted By: MR_P_BODY

Re: holley 750 vac issues - 01/08/13 02:57 AM

Sounds like the pump shot is late... make sure as soon
as the throttle moves its getting the pump shot
Posted By: HOTMOPR

Re: holley 750 vac issues - 01/08/13 03:35 AM

I have the pump arm gap at .015
Posted By: BSB67

Re: holley 750 vac issues - 01/08/13 03:39 AM

Is it a Holley - 3310? A slight stumble while cruising with light throttle can be caused by some junk in the carb causing a lean condition in the transition or possibly main circuit. That has been my experience more than once on Holleys.
Posted By: HOTMOPR

Re: holley 750 vac issues - 01/08/13 03:51 AM

yes its a 3310. I had it all apart and it was cleaned and reassembled.
Posted By: MR_P_BODY

Re: holley 750 vac issues - 01/08/13 04:10 AM

Are you good getting up to cruise and then it wont
take any pedal... could be your secondary is opening
to easy... put a slightly stiffer spring in it
Posted By: HOTMOPR

Re: holley 750 vac issues - 01/08/13 04:57 AM

It seems to stumble at lower rpms. Unfortunatly The weather has been crappy and I havent had much chance to drive it since I got it running. It runs great in the shop. Idle and throttle response is great but under load its a different story.
Posted By: 340SHORTY

Re: holley 750 vac issues - 01/08/13 05:03 AM

I had that problem. I went up to the next size squirter and adjusted the pump screw to let it squirt sooner..
Posted By: HOTMOPR

Re: holley 750 vac issues - 01/08/13 05:11 AM

I thought about trying a bigger squirter. I guess I'll try closing up that pump gap also since Mr p mentioned that too. I know bigger squirters helped my starting line bog on my 980 double pumper..
Posted By: 540DUSTER

Re: holley 750 vac issues - 01/08/13 07:43 AM

the gap is measured with the throttle open all the way,not at idle.
Posted By: Dragula

Re: holley 750 vac issues - 01/08/13 12:49 PM

On Mopar's a vacuum carb should never be used...But it also sounds like you squirter shot is a little late or small or both.
Posted By: dogdays

Re: holley 750 vac issues - 01/08/13 06:37 PM

There are also about 10 different accelerator pump cams to try.

R.
Posted By: MR_P_BODY

Re: holley 750 vac issues - 01/08/13 08:39 PM

Quote:

It seems to stumble at lower rpms. Unfortunatly The weather has been crappy and I havent had much chance to drive it since I got it running. It runs great in the shop. Idle and throttle response is great but under load its a different story.



Also make sure you have enough timing
Posted By: sixpackgut

Re: holley 750 vac issues - 01/08/13 09:42 PM

Quote:

the gap is measured with the throttle open all the way,not at idle.



this
Posted By: Guitar Jones

Re: holley 750 vac issues - 01/08/13 09:46 PM

Quote:

On Mopar's a vacuum carb should never be used...But it also sounds like you squirter shot is a little late or small or both.



Uh why? I've used vacuum sec carbs for years on my race car to slow it down. A screw and a lock nut on the vacuum pod cap stops the opening very well.
Posted By: cgall

Re: holley 750 vac issues - 01/09/13 04:15 AM

There are a whole range of different springs that are color-coded to vary the opening timing and duration of the the secondaries. They have a dab of paint on the small end of the spring. IIRC, the gold spring was the lightest one that was used at the strip. You might check your carb gaskets and hoses to make sure you don't have an air leak there. I run a 950HP carb that has a vac-sec pot on it, silver spring. It has been 10.24 at 128 MPH on my Duster.
Posted By: HOTMOPR

Re: holley 750 vac issues - 01/22/13 03:33 AM

Quote:

I thought about trying a bigger squirter. I guess I'll try closing up that pump gap also since Mr p mentioned that too. I know bigger squirters helped my starting line bog on my 980 double pumper..



PUNTING!! I give up on the 750! I went back to my 850 dbl pumper. Problem I am having with this carb is I cant get it to idle down. I welded up the drilled primary throttle blades. The secondaries are not drilled and it doesnt have the secondary idle adjustment. Right now the best I can get it is 1100 rpms. Which might be fine in a auto with a bigger cam but the 4 speed likes about 800. Any ideas why it wont idle down. No cables were hooked up so nothing is binding. blades appear to be closed when looking down inside.. I also sprayed carb cleaner around it and no vacuum leaks.. Any Ideas?
Posted By: lewtot184

Re: holley 750 vac issues - 01/22/13 03:41 AM

Quote:

I have the pump arm gap at .015

if you have an air gap between the arm and pump lever at idle, thats wrong. no air gap.
Posted By: 70AARcuda

Re: holley 750 vac issues - 01/22/13 04:09 AM

flip the carb over..there is a set screw that allows the rear throttle blades to be opened to help with the idle..see if some one has opened them up too much...
Posted By: HOTMOPR

Re: holley 750 vac issues - 01/22/13 04:11 AM

No air gap and this 850 doesnt have the secondary idle adjustment..
Posted By: 70AARcuda

Re: holley 750 vac issues - 01/22/13 05:01 AM

Quote:

No air gap and this 850 doesnt have the secondary idle adjustment..



my secondary throttle blades was in reference to the 750 vac.

on the 850...you may have an internal leak..check gaskets..make sure the power valve is tight and center on the gasket..
Posted By: Evil Spirit

Re: holley 750 vac issues - 01/23/13 04:38 PM

Quote:

On Mopar's a vacuum carb should never be used...But it also sounds like you squirter shot is a little late or small or both.



There's a LOT of hard running Mopars out there that run vacuum secondary carbs, not to mention the 6 barrel guys.

While it takes a different approach to tune them, they are no harder to tune than double pumpers and are a lot more forgiving to concessions to make a car more street friendly, such as a tight converter or not enough gear.
Posted By: Paul_Fancsali

Re: holley 750 vac issues - 01/23/13 09:47 PM

Late opening power valve Vac carb and on the dbl pumper leave it at 1100 runs better cold.
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