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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old September 26th, 2014, 05:17 PM
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Question Holley Carburetor Conversion

Hello,

I havenít posted to the board much but I would like some help in doing the carburetor conversion from the Stromberg to the Holley. I have a 1962 1000 truck with a 305D engine. I have already upgraded to the electric fuel pump.

I donít have the tools or expertise to do this conversion so I am going to have a garage mechanic do the work. He would like me to source the parts.

I started with the information on the http://6066gmcguy.com site on the Holley 500 CFM 2-BBL #4412 page but the part numbers have changed since it was written.

I located the following parts at Jegís:

The Holley 500 CFM 2-BBL
Holley #510-0-4412C
http://www.jegs.com/i/Holley/510/0-4...rentProductId=

Mr. Gasket Adapter
Adapter #720-1937
http://www.jegs.com/i/Mr-Gasket/720/1937/10002/-1

Can anyone verify the above part numbers I have located for the conversion? Also, are there any other parts I should consider or will need?

One last question, will my original oil bath air filter fit on top of the new carburetor?

Any other recommendations to consider would also be welcome as I feel I am flying blind here.

Thanks for your help.

Brian
Santa Rosa, CA
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  #2  
Old September 26th, 2014, 08:28 PM
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Andice Andice is offline
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Default Re: Holley Carburetor Conversion

The carb adapter that I used on my Holley was Mr Gasket #1937 from O'Reilly.
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Old September 26th, 2014, 08:37 PM
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Default Re: Holley Carburetor Conversion

I am almost 100% certain that the carb you posted is the same one that I used but you might want to wait for somebody else to chime in before you pull the trigger.

The installation was very easy - I even helped. We had done an engine swap from a '66 to my '64 and added the Holley a few months later. The adapter is required and you may have to purchase a different return spring and perhaps tweak the rod coming from the accelerator linkage. In my case I think we added a different return spring mounting "bar" so the spring would not interfere with the larger carb.

Ive attached a before and after. Sorry the images are so small. I hope they help.
Attached Images
File Type: jpg 201124.jpg (20.8 KB, Multiple views, 30 clicks)
File Type: jpg 201308b.jpg (64.2 KB, Multiple views, 28 clicks)
File Type: jpg 201207.jpg (142.6 KB, Multiple views, 26 clicks)
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Old September 27th, 2014, 07:52 PM
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Default Re: Holley Carburetor Conversion

Welcome Brian62GMC,

You have to modify the stock air cleaner to fit or just go aftermarket.

You can bolt this upgrade on, but some suggest you remove the intake manifold (*Need new intake gasket) and enlarge the opening to match the adapter.

Also I think you will need a longer manual choke cable. Some folks have played around with jetting the carb down, but that can be done later once you see how it runs. You should be pleased.

Which electric fuel pump are you using? I think the Holley requires 4-7 psi.

Any photos of your truck? Good luck with your conversion. Henry
Attached Images
File Type: jpg gmc intake non magnum.jpg (33.5 KB, Multiple views, 8 clicks)
File Type: jpg IMG_2669.JPG (1.20 MB, Multiple views, 9 clicks)
File Type: jpg IMG_2667.JPG (1.18 MB, Multiple views, 8 clicks)
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Old October 2nd, 2014, 07:15 PM
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Default Re: Holley Carburetor Conversion

Brian, all the part numbers are correct but you'll need a different air cleaner to accommodate the large air intake of the Holley.Definitely take Funky61's advice on opening up the manifold base, I've done the same myself in the past. If you ever need some hands on help I'm just roughly 5-7 miles south of you in Rohnert park.
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Old October 2nd, 2014, 07:16 PM
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Default Re: Holley Carburetor Conversion

Brian, all the part numbers are correct but you'll need a different air cleaner to accommodate the large air intake of the Holley. Definitely take Funky61's advice on opening up the manifold base, I've done the same myself in the past. If you ever need some hands on help I'm just roughly 5-7 miles south of you in Rohnert park.
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Old October 3rd, 2014, 03:35 AM
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Default Re: Holley Carburetor Conversion

Brian,

I did the Holley conversion last year on my 1964 3/4 ton GMC pickup with a 305E engine. It had been a long time since I worked on cars, but this was not a hard job. However, there are other parts you will need.

Funky61 is right about the air cleaner. The Holley requires a standard (5 1/8" if I remember right) diameter intake opening. I was told that this was common on 1970's GM cars, so I got an air cleaner from a mid-70's Impala that fit perfectly. It even had a spot for the oil breather line (which you may or may not have depending on the model year).

I was lucky that my accelerator spring set-up worked without need for changes.

I was able to use my existing choke set-up, but the cable is really too short (it had to go through the ignition wires at the distributor) and I eventually installed a longer one from Napa.

I also had a challenge in finding a gas line connection that fits the carburetor and the fuel line. I think Holley makes a part that will work and can be purchased from dealers like Summit Racing. You will probably have to convert the line from the fuel pump to the carburetor connection to a flexible fuel line hose that will require clamps. I added an in-line filter at this point as a backup to a larger filter ahead of the fuel pump.

I did not enlarge the intake manifold opening, but will defer to more experienced members about the need for this. I can tell you that my truck has more power and runs better with the Holley, with some loss of gas mileage - but I am still getting about 13 mpg from open road type driving. My next engine project is to reduce the carburetor jet size because the truck seems to be running rich.

JRMunn
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Old October 3rd, 2014, 07:04 PM
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Default Re: Holley Carburetor Conversion

Thanks for all the feedback.

I went ahead and ordered the adapter from OíReillyís and the carburetor from Jegís. Should have them in a couple of days.

The fuel pump I installed was the Carter P4070 with a PSI of 4-6 or 8 depending on which document I was looking at.

I guess I was assuming the adapter would fit the manifold exactly but then it wouldnít be a universal adapter. Is expanding the manifold something a machine shop would do or can any repair shop handle that?

I donít think Iíll modify the old air filter but I would like to get a replacement that looks something like the original, at least black. The chrome ones I see on the internet look too modern for me. Iíll shop after I get the carburetor.

Sounds like all the other adjustments will have to be dealt with as the installation progresses.

Thanks for the help. I have had so many manual fuel pumps break down after a couple of months and now the carburetor is gummed up so I have to use the choke to get any power going up hill. I decided to cut my losses and make the conversion.

Bigblock will understand that I had to turn around above Willits on 101 because I couldnít get up the long hills without full choke. At least I didnít get towed home that time.

Brian
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Old October 3rd, 2014, 07:11 PM
bigblockv6 bigblockv6 is offline
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Default Re: Holley Carburetor Conversion

Brian, Anyone with a die grinder and the correct bit can enlarge the opening on the manifold base so you don't necessarily need to go to a machine shop as they would charge much more for a simple modification.
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Old October 4th, 2014, 12:18 AM
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Default Re: Holley Carburetor Conversion

Brian,

BigBlockV6 has just described how I ended up doing this. My effort did not look "machine shop perfect/smooth," but it was some thing simple I can say I did myself and not difficult.

The fuel pump you are using is also the one I use. I also added an oil pressure safety switch and an inertia switch in the event of an accident.
Plus there's a relay in the circuit that I believe keeps it from overheating the pump/circuit. They have kits for this as well.

The inertia switch I got at the junkyard from a '96 ford contour and the other switch I bought from Summit. Here are some links;

http://www.summitracing.com/parts/sum-890145/reviews/

http://www.summitracing.com/parts/crt-a68301

http://www.smartracingproducts.com/f..._manual_v1.pdf

http://www.summitracing.com/parts/tfs-25004k
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