Holley 750 double pumper rich/floods at idle - Chevelle Tech
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post #1 of 27 (permalink) Old Sep 10th, 12, 4:52 PM Thread Starter
 
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Holley 750 double pumper rich/floods at idle

I've got an older 750 on my 69 396. I'm having "loading up" problems at or near idle. It has vacuum secondaries, not running a choke. Running this past a few friends I've got many different ideas. One seemed most sensible. Because of my cam .544 dur is 230 with 109 lobe center. I have low vacuum (10"). He said the secondary spring is probably opening the secondaries near idle.
How do i check for this and is there a way to choose the right spring.
Or.... any other ideas? I have the floats lower than the sight glass now, checked the needle/seat for shut off, and it's spotless inside, no varnish or dirt.
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post #2 of 27 (permalink) Old Sep 10th, 12, 4:59 PM
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Re: Holley 750 double pumper rich/floods at idle

Quote:
Originally Posted by memo3189 View Post
I've got an older 750 on my 69 396. I'm having "loading up" problems at or near idle. It has vacuum secondaries, not running a choke. Running this past a few friends I've got many different ideas. One seemed most sensible. Because of my cam .544 dur is 230 with 109 lobe center. I have low vacuum (10"). He said the secondary spring is probably opening the secondaries near idle. How do i check for this and is there a way to choose the right spring.
Or.... any other ideas? I have the floats lower than the sight glass now, checked the needle/seat for shut off, and it's spotless inside, no varnish or dirt.
First, you need to determine what carb you have.

A "Double Pumper" ONLY has mechanical secondaries, and NEVER has vacuum secondaries... A "Vacuum secondary" carb with the spring housing is not a "Double Pumper, and should only have an accelarator pump on the front (primary) side of the carb... Unless its been assembled from a hodge-podge of parts (not even sure it would work)...

The "secondary" spring should not matter at idle...

Could be the Power Valve, either blown or incorrect... Its been a while, but as a rule of thumb/baseline, the Power valve should be around half on what the vacuum is as idle... For 10" at idle, I install a 5.0 Power valve to start...


If you do have a true Double Pumper, then maybe you have too much pump shot coming in too soon... Double Pumpers can be finicky down low, as their really intention was for all out WOT, with little consideration for idling very much...

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Last edited by 1966_L78; Sep 10th, 12 at 5:17 PM.
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post #3 of 27 (permalink) Old Sep 10th, 12, 5:18 PM
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Re: Holley 750 double pumper rich/floods at idle

Yeah, check the power valve. The only way I know to do so it to "suck it" an see if it holds.

Not going to debate Tony's recommendation of a 050 powervalve, as it what Holley would tell you BUT you can run higher rated ones without them dumping fuel through the venturies if the whole carb is properly set up.

Use a 065 which is pretty much stock Holley. Likely its the one you'll find inside.

And I simply cannot imagine the engine pulling enough cfm at idle to move the secondary flaps at all unless something is amiss with the secondary vacuum system.

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post #4 of 27 (permalink) Old Sep 10th, 12, 5:19 PM
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Re: Holley 750 double pumper rich/floods at idle

Quote:
Originally Posted by memo3189 View Post
I've got an older 750 on my 69 396. I'm having "loading up" problems at or near idle. It has vacuum secondaries, not running a choke. Running this past a few friends I've got many different ideas. One seemed most sensible. Because of my cam .544 dur is 230 with 109 lobe center. I have low vacuum (10"). He said the secondary spring is probably opening the secondaries near idle.
How do i check for this and is there a way to choose the right spring.
Or.... any other ideas? I have the floats lower than the sight glass now, checked the needle/seat for shut off, and it's spotless inside, no varnish or dirt.
Vacuum secondary spring has nothing to do with manifold vacuum. To much fuel pressure will cause the needle/seat to open, or the float itself is not sinking to bottom. Check the gasket between to throttle body and carb body if it's properly sealed.
A power valve is most likely rupture do to backfire. If you have not install a check valve in the throttle body.

Louis
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Last edited by lg1969; Sep 10th, 12 at 5:47 PM.
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post #5 of 27 (permalink) Old Sep 10th, 12, 5:22 PM
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Re: Holley 750 double pumper rich/floods at idle

Louis is right on the fuel pressure. I think Holleys can take 8-9 psi though.

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post #6 of 27 (permalink) Old Sep 10th, 12, 5:25 PM
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Re: Holley 750 double pumper rich/floods at idle

If this has been played with ,the floats may have gotten switched and that doesn't work.
From Holley
Quote:
Use of brass floats on the secondary side of Model 4160 Carburetors factory equipped with nitrophyl secondary floats such as part number 0-3310C for Example, may cause the float to contact the metering plate resulting on loss of fuel control and flooding.
Also ,as it was brought up ,if parts were swapped ,you may have a metering block on the secondaries where a metering plate should be.
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post #7 of 27 (permalink) Old Sep 10th, 12, 5:28 PM
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Re: Holley 750 double pumper rich/floods at idle

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Originally Posted by 427L88 View Post
Louis is right on the fuel pressure. I think Holleys can take 8-9 psi though.
Too much. should be 5-6 psi.

Louis
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post #8 of 27 (permalink) Old Sep 10th, 12, 5:33 PM
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Re: Holley 750 double pumper rich/floods at idle

Quote:
Originally Posted by Mike View Post
If this has been played with ,the floats may have gotten switched and that doesn't work.
From Holley

Also ,as it was brought up ,if parts were swapped ,you may have a metering block on the secondaries where a metering plate should be.
3310-1 yes on the metering block
3310-2 on up, no
3310-1 = 780cfm
3310-2 on up, 750cfm

Louis
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post #9 of 27 (permalink) Old Sep 10th, 12, 6:47 PM Thread Starter
 
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Re: Holley 750 double pumper rich/floods at idle

Ok went out and checked carb. It's a 3310-11. Holley says it is a 4160.
I took the vacuum cap off for the diaphram and it looks like an old accoridian. All wrinkles. The holley site shows this as "junk". Also it has a silver spring, Holley says to try a black spring.
Now... where is the power valve?? So I can see what size I have.
Ohhhh fuel pressure is 7psi, vacuum was 10" @ idle up to 11oo rpm.

On the Holley site it says this was the stock carb for a 375HP which I have.
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post #10 of 27 (permalink) Old Sep 10th, 12, 6:51 PM
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Re: Holley 750 double pumper rich/floods at idle

Quote:
Originally Posted by memo3189 View Post
Ok went out and checked carb. It's a 3310-11. Holley says it is a 4160.
I took the vacuum cap off for the diaphram and it looks like an old accoridian. All wrinkles. The holley site shows this as "junk". Also it has a silver spring, Holley says to try a black spring.
Now... where is the power valve?? So I can see what size I have.
Ohhhh fuel pressure is 7psi, vacuum was 10" @ idle up to 11oo rpm.

On the Holley site it says this was the stock carb for a 375HP which I have.
Power valve is in the metering block, which is the 5/8" or so block that is sandwiched between the main body of the carb, and the fuel bowl.

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post #11 of 27 (permalink) Old Sep 10th, 12, 8:44 PM
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Re: Holley 750 double pumper rich/floods at idle

Floats too high?

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post #12 of 27 (permalink) Old Sep 10th, 12, 9:13 PM
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Re: Holley 750 double pumper rich/floods at idle

Were the idle mixture screws tuned by vacuum? If so, was it done with vac advance disconnected and the port on the carb plugged? A 540 cam really isn't huge for a 396 as I ran similar in a 350. You should be able to get tuned more around 12" between timing and carb. What is your initial timing set at? If this is while driving or taking off from a start have you tried using a smaller pump shot nozzel?

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post #13 of 27 (permalink) Old Sep 10th, 12, 9:23 PM
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Re: Holley 750 double pumper rich/floods at idle

Holleys cant use more than 5-6?
Think my carter 172 puts out 8ish...no problems yet but dont want to ruin it.


Quote:
This post is a duplicate of a post that you have posted in the last five minutes.
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post #14 of 27 (permalink) Old Sep 11th, 12, 9:24 AM Thread Starter
 
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Re: Holley 750 double pumper rich/floods at idle

Where is the best place to get Holley parts? I live in Western New York.
Is there a kit with various springs, valves, jets available?
My initial adv is 12deg with limiters for total of 36, no vac adv.
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post #15 of 27 (permalink) Old Sep 11th, 12, 11:18 AM
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Re: Holley 750 double pumper rich/floods at idle

Google it, And I do not think Holley made -11 in 69. -1 yes. -11 does not exist. It only goes up to -6

Louis
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Original owner
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https://www.youtube.com/watch?v=53OG2K2P9vQ
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