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GMC V6 and V12 Engines Engine repair and rebuilding

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  #31  
Old October 19th, 2019, 12:11 AM
jerrspud jerrspud is offline
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Default Re: 305e Holley 500 swap question

Hello. Power Valve question.

Everything is working fine, still very rich on idle. Silly me... I finally adjusted the idle screws in and vacuum when up so I'm on the right track. I probably turned them in almost a full turn to get the best vacuum. I read the specs on the stock carb and the power valve is a 5. My Vacuum is 17-19 so I'm assuming I need a much larger power valve then a five. Anyone put a higher number in?

and if I do put in a higher number... I would dump more fuel at acceleration right?

specs
https://www.holley.com/products/fuel...b0e_ENCG868neA
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Last edited by jerrspud; October 19th, 2019 at 12:32 AM.
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  #32  
Old October 19th, 2019, 12:49 AM
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Default Re: 305e Holley 500 swap question

I did not change the power valve but I did use lower number jets. I believe I used 68"s.
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  #33  
Old October 19th, 2019, 02:45 AM
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Default Re: 305e Holley 500 swap question

Running rich at idle is usually the float is too high. Adjust the float level until it barely come out the sight hole on the right side of the bowl. If you do not have the instruction be sure to download the instruction from the web site.

Power valve is just fine like it is. It only open when the vacuum drop to 5" of vacuum, it is for fuel enrichment during full throttle operation. Changing it to a higher number will not help your acceleration, it could make your engine run worst by making it run too rich too soon.

If you have acceleration issue will need to make changes on your discharge nozzle (stock is a 28). When you snap open the throttle and it backfire through the carb you need a larger nozzle, I would go to a 35 and see if the would help. If it bog down then accelerate OK the you need to go to a smaller nozzle, maybe a 24. You can go up or down from there to get the best response. There is a couple of other adjustments that can help fine tune it if needed. Here a link for some of the different sizes:
https://www.summitracing.com/search/...charge-nozzles
Also I would stay with the same style of nozzle.

Once the above is working right the recheck the idle speed and idle mixture.

Keep us posted on the progress good or bad so we can get the engine running great.
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  #34  
Old October 21st, 2019, 04:23 PM
jerrspud jerrspud is offline
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Default Re: 305e Holley 500 swap question

Quote:
Originally Posted by Funky61 View Post
I did not change the power valve but I did use lower number jets. I believe I used 68"s.
Yeah... I was kinda thinking to leave it alone. It's definitely got more then enough fuel now, and I don't need to dump more in with a higher number Power Valve. I have 70 mains in it right now, and it's still a a little rich. I can see white some when I rev the motor from idle. The rich idle is much better since I turned in the idle screws. I even had to turn down the idle speed a bit so that's another sign I'm on the right path turning down the idle mixture.


Quote:
Originally Posted by James View Post
Running rich at idle is usually the float is too high. Adjust the float level until it barely come out the sight hole on the right side of the bowl. If you do not have the instruction be sure to download the instruction from the web site.
Float level is fine. This is a 500CFM carb on a motor that doesn't need that much fuel. So I'm trying to get it dialed in to match the motor a well as possible.
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Last edited by jerrspud; October 21st, 2019 at 04:33 PM.
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  #35  
Old December 1st, 2022, 07:13 PM
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Default Re: 305e Holley 500 swap question

Quote:
Originally Posted by TJ's GMC View Post
Put an HEI in as well if you don't already have one to help burn the fuel. I'm running a 500 cfm eddy 4 barrel on my 305E. Opened up a magnum intake. It's way more than the engine needs, but ready for the future 401 or 478 I may find.
@TJ, what are these things in your fuel system?
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  #36  
Old December 1st, 2022, 07:25 PM
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Default Re: 305e Holley 500 swap question

Quote:
Originally Posted by AngryPirate View Post
@TJ, what are these things in your fuel system?
Fuel pressure regulator.
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