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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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AngryPirate AngryPirate is offline
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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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  #37  
Old April 3rd, 2023, 12:33 AM
jgpnashville jgpnashville is offline
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Default Re: 305e Holley 500 swap question

I have a super-low mileage blue '67 K15 with the 305E that I bought earlier this year (it had been parked for >20 years). After replacing brakes and working on the fuel system, I replaced the Stromberg WW with a Holley 4412S 2BBL, but kept the mechanical fuel pump (for now).
The engine runs well, but doesn't idle consistently. I'm not sure I have vacuum connected everywhere correctly. The Stromberg WW had just one vacuum port, but the Holley has 3 vacuum ports - one on the throttle body (power brake or PCV vacuum port according to Holley pdf), the timed spark vacuum port on the choke side that was capped from the factory, and the full manifold vacuum port on the front, under the fuel inlet. I tee'd the single vacuum line from the distributor to the power brake/pcv port on the throttle body, and to the full manifold vacuum port, while leaving the timed spark port on the left side capped.
Something just doesn't seem right - the engine will either idle really high, like 1800-2000 rpm, or drop down to a more standard 700 rpm. I also struggled with the carb return spring - the one from the Stromberg was too stiff and pulls the throttle back into no-man's land when you let off the accelerator where the engine dies. Removing that spring allows the carb's built-in return spring to pull the accelerator back normally, but I know some sort of spring is supposed to be added.
I drove it on city streets today for the first time and it died on me, after stopping to put 15 gallons of gas in. It was seemingly for lack of fuel. The see-through fuel filter I added below the fuel pump was empty, even after just filling up the tank. So, I had it towed home and I'm not sure where to go next. The fuel filter is full of gas now that it's home (off the wrecker), but it just seems out of sorts.
Do I have the vacuum lines connect properly, or should I investigate something else first?
Thanks!
Am I better
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  #38  
Old April 3rd, 2023, 01:38 AM
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Default Re: 305e Holley 500 swap question

The ported vacuum (timed spark vacuum port) on the choke side in the metering block does nothing on the 4412, the throttle plate base does not have the hole in to allow that to work. I had drill the hole in my throttle plate base and the gasket to allow this feature to work on the metering block. Depending on how old your 4412 is, the ported vacuum is either on the metering block or on the throttle plate base below the choke or both. If it is on the throttle plate base it should be functional. Back in the day (correct me if I'm wrong) all of the distributor vacuum cans went to manifold vacuum. So that third fitting (on the front of the throttle plate base) I believe is manifold vacuum, if that what you have that is where the distributor vacuum can gets connected to. With tighter emission it got moved to ported vacuum. If you chose to use ported vacuum you have to readjust the idle up and maybe advance the distributor timing a few degrees from specs.

As for the throttle return spring, buy any spring that will give enough pull to keep the throttle close and still allow full throttle. The one on the carburetor normally not enough to keep the throttle close once installed on the manifold.

On the subject of fuel, did the engine start after you got home? Have you check the fuel pressure with a gauge tee in? Did you check the fuel level in the fuel bowl after you been cranking for a few seconds (without pumping the throttle)?

Let us know what you figure out.
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  #39  
Old April 13th, 2023, 02:17 PM
jgpnashville jgpnashville is offline
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Default Re: 305e Holley 500 swap question

Yes, the truck started when I got it home, but after some more thought, I capped the PCV/Power Brake vacuum line on the throttle body side of the Holley carb, since the truck doesn't have power brakes or a PCV line. This means that the timed spark vacuum port under the choke is capped, as is the power brake/PCV vacuum. Doing this has helped it idle much better, but maybe the timed spark vacuum and the full manifold vacuum lines should both be connected via tee to the vacuum line from the distributor. I'll try that next.

I bought a collection of throttle return springs from O'Reilly's and installed one of the lighter springs, which seems to provide enough tension to return the throttle back closed. The fuel level in the bowl seems to be about right - it was right at the edge of the screw hole on the side, but I haven't measured it after cranking with no throttle. It is worth mentioning that the truck starts so much better when cold with the Holley vs the Stromberg - I rarely have to touch the choke, but it also hasn't been much below 50 degrees F, either.
The only issue now is the engine has a tendency to die when coming to a stop, such as approaching a stop sign or traffic light. It restarts easily, but something isn't right with fuel delivery. I'm wondering if the engine is being flooded since the Holley 4412 has the original jets in it and may be over-providing fuel to an engine such as the 305e. Once when it died at a light, I smelled gas, so that has me wondering. It's worth noting that when I put the clutch in to coast toward a light, if I give it some throttle, the engine won't die.
I haven't tested fuel pressure with a gauge and tee, since I don't own one, but perhaps that's worth buying for this issue, if after connecting the timed spark vacuum port with a tee doesn't improve the way it runs when coming to a stop.

Thanks for all your suggestions. The truck is coming along and while the manual steering takes some getting used to, as does the SM420 shifter, notably downshifting from 3rd to 2nd seems touchy and a bit hard to find 2nd consistently, it's going to be a great vehicle.
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  #40  
Old April 13th, 2023, 07:52 PM
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Default Re: 305e Holley 500 swap question

My direction to you is to start with backing down the jets - that carb is overkill on fuel metering when it comes to a 305. Did you check your power valve to see it's not ruptured? Holley's been known to blow their power valve if the engine back-fires thru the carb. What kind of exhaust system do you have? With any engine when you start feeding it more gas - you need to increase the air flow - usually this is done with increased cam lift/duration and timing adjusted to comsume the increased fuel - and then you need to be able to get rid of the increased volume of exhaust. My advice is to get a good flowing exhaust system before you do anything else. What goes in - must come out.
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