Holley 4150 780cfm woes. - Chevelle Tech
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post #1 of 15 (permalink) Old Feb 11th, 20, 8:41 AM Thread Starter
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Brian
 
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So after replacing plugs due to a no start (was running too rich) I decided to tune the Holley. I bought the carb many years ago with a fresh rebuild and it worked for a few months and 300 miles.
I checked the idle mixing screws and they were 2 3/4 turns out, so I set them both in 1 1/2 turned out
Next was to check float levels.

First issue. Disconnected coil, cranked engine to prime bowls with mechanical fuel pump. No fuel getting to front bowl? Completely removed front float adjustment screw and it was free and clean. Thinking it may be clogged inlet fuel filter in Holley?

Second issue, when I cycle the throttle linkage, I get fuel leaking front the main linkage shaft at the carb body?

Here’s my set up. The stainless fuel line crosses over the valve cover to a Y block.
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Last edited by 72soft-top; Feb 11th, 20 at 9:06 AM.
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post #2 of 15 (permalink) Old Feb 11th, 20, 9:03 AM
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Re: Holley 4150 780cfm woes.

Quote:
Originally Posted by 72soft-top View Post
Thinking it may be clogged inlet fuel filter in Holley?

Possible. Only way to know is take the fuel line off and see if anything is coming out of it when you crank the engine.



Quote:
Originally Posted by 72soft-top View Post
Second issue, when I cycle the throttle linkage, I get fuel leaking front the main linkage shaft at the carb body?

Thats somewhat normal. When you pump the throttle the accelerator pump is shooting fuel right on top of the closed throttle blades and there is nowhere for it to go except for out of the shaft which is not a perfect fit even when new.



I would have to wonder though, if you are getting fuel from the accelerator pump, there should be fuel in the fuel bowls. How long has it been sitting ?

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post #3 of 15 (permalink) Old Feb 11th, 20, 10:08 AM Thread Starter
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Been sitting since the Fall. Before I cranked, I removed both bowl site plugs and obviously they were both low. After I cranked, the rear bowl came right up to level and front bowl was empty?

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post #4 of 15 (permalink) Old Feb 11th, 20, 10:21 AM
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Re: Holley 4150 780cfm woes.

Suspect Holley filter or y block teflon tape plug right side? I have my filter removed and one in line.
You could fill the front bowl through the vent tube, fire the engine up and see what happens at the float level pug upon shut off.

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post #5 of 15 (permalink) Old Feb 11th, 20, 11:56 AM Thread Starter
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Removed bowl and no filter is installed. Used some tubing to test fuel pump and it pumps.

Took float assembly and needle out for inspection, no issues discovered. Of coarse the bowl screw gaskets are now trashed so I have to get some replacements for reassembly.

My plan is to put it back together and try to fire it up to see if the bowl fills?

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post #6 of 15 (permalink) Old Feb 11th, 20, 1:45 PM
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Re: Holley 4150 780cfm woes.

..and adjust the needle until it does! You can "rough it" by turning the bowl upside down and seeing where the float hangs. It helps to get it close this way.

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post #7 of 15 (permalink) Old Feb 11th, 20, 3:54 PM Thread Starter
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Got it fired up. Then shutdown to check front bowl level. It was good! Not asking why... just glad it’s good.

Tuned the idle mixing screws and got about vacuum of about 15” idoling at 700rpm. That’s probably pretty good for the cam (Voodoo 60203 FT)

Did get a major backfire after I leaned it out too much and hit the throttle. That scared me for a sec but I think it’s good now

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post #8 of 15 (permalink) Old Feb 11th, 20, 4:16 PM
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If that’s a really old Holley, change power valve. Prolly blew it.
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post #9 of 15 (permalink) Old Feb 11th, 20, 4:22 PM Thread Starter
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Quote:
Originally Posted by Reelysalty View Post
If that’s a really old Holley, change power valve. Prolly blew it.
Not sure of age, but it’s been rebuilt. How would you determine if the power valve is blown?

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post #10 of 15 (permalink) Old Feb 11th, 20, 5:56 PM
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https://forums.holley.com/entry.php?...r-Valve-Tuning

One way is turn idle screws shut, if engine keeps running chances are PV blown.

No big deal, you prolly have to change anyway for your app.
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post #11 of 15 (permalink) Old Feb 11th, 20, 6:01 PM
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Re: Holley 4150 780cfm woes.

If the P/V is blown you will know it, lots of black smoke.


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post #12 of 15 (permalink) Old Feb 12th, 20, 9:46 AM
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Re: Holley 4150 780cfm woes.

It will run like crap and stall.

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post #13 of 15 (permalink) Old Feb 12th, 20, 1:46 PM Thread Starter
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So now I replaced the torn fuel bowl screw gaskets with nylon ones from the Mr Gasket kit and they leak. Any tips for seating these or are the nylon ones crap? Originals weren’t nylon.
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post #14 of 15 (permalink) Old Feb 12th, 20, 2:17 PM
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Re: Holley 4150 780cfm woes.

Quote:
Originally Posted by 72soft-top View Post
So now I replaced the torn fuel bowl screw gaskets with nylon ones from the Mr Gasket kit and they leak. Any tips for seating these or are the nylon ones crap? Originals werenít nylon.
Have not had any trouble with the nylon washers. I do not use the slot screws in Holley's anymore just the ones with the hex head bolts as they tighten up better. Check that bowl out carefully, might have a hairline crack.


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post #15 of 15 (permalink) Old Feb 12th, 20, 2:30 PM Thread Starter
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I think I got it. Backed it out and re tightened. I think it may have been cocked a little?

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