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Old 05-11-2014, 03:26 AM   #1
frankenstien
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Default carb swap issues

so im swapping out my edelbrock 750 for a Quick Fuel technology 750, having some vacuum line issues, seeing if anyone has done a similar swap and run into these issues.

i am running a professional products crosswind intake manifold( pretty close to an edelbrock performer air gap rpm)

problem - ill have to plug the vacuum port in the manifold for my trans, as the fitting is too tall and the float bowl hits it and will not seat fully on the carb pad.

the stuff i need vacuum for is my brakes, transmission, and heater controls, the distributer is ran by an msd box and is all mechanical advance.

the carb only has 1 3/8'' port- brakes- instructions say use for brakes or pcv, my pcv is vented to atmosphere

1 manifold vacuum port- transmission
2 timed vacuum ports- not really needed

the dilema im having is should i T the trans and hvac together? seems like a bad idea to me?

or just hook my timed vacuum port to it and call it a day, it does have a vacuum canister for the hvac so probably be ok?

this is on a 1974 gmc truck with a healthy 383

thanks
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1974 3/4 ton gmc
450+HP 383

2005 GMC 2500HD Duramax Diesel- 452hp/962tq on P3's dyno

2015 Ford Expedition EL - Wife's rig
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Old 05-11-2014, 04:30 AM   #2
ChevyMan0784
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Default Re: carb swap issues

Why dont you run an inch spacer under your carb for clearance and better air fuel mixture? Run the 4 bore one for low end power, open plenum for higher end power. That is what I do to run my THM400 vacuum off the manifold. I also run a 90 off the port so that the hose still clears as well. Would that help your situation? Oreilly carries a combo type that has a removable 4 bore center. Maybe 30 bucks?
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Old 05-11-2014, 06:45 PM   #3
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Default Re: carb swap issues

I was using a 4 hole spacer, been having trouble getting the old carb tuned to the different can for about a year, that's the only reason I used the spacer was to see if it helped. But that may be what needs to happen. I would like it to be the last resort
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1974 3/4 ton gmc
450+HP 383

2005 GMC 2500HD Duramax Diesel- 452hp/962tq on P3's dyno

2015 Ford Expedition EL - Wife's rig

Last edited by frankenstien; 05-11-2014 at 11:41 PM.
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Old 05-11-2014, 11:51 PM   #4
ChevyMan0784
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Default Re: carb swap issues

I am not sure that putting a T for the trans and HVAC would be the best idea. But, I dont see what it would hurt to just try and see how it works. If everything works, run it for a bit and see how the trans acts. Also, you could drill and tap your intake in a different area to accomodate the carb. Aside of taking off the manifold, doesnt seem like too difficult of a thing to do. Just another idea/thought.
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Old 05-12-2014, 11:07 AM   #5
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Default Re: carb swap issues

Thought about drilling and tapping with a vacuum, was just going to run the spacer, but the carb has an X shaped cut out in the base of the carb that the 4 holes share, and I don't know how running a spacer super close would effect that, so I'm going to wing the vacuum lines, but the T may not be an issue as it has a vacuum canister, we will see, just want this thing to work right
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450+HP 383

2005 GMC 2500HD Duramax Diesel- 452hp/962tq on P3's dyno

2015 Ford Expedition EL - Wife's rig
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Old 05-19-2014, 01:02 PM   #6
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Default Re: carb swap issues

If your 383 has a long duration cam, it may have a weaker vacuum signal, so tying both the signals may not work. I would think there would be combination of fittings to make it work, failing that there should be an alternative place for tapping a vac port in the manifold. Good luck!
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Old 05-22-2014, 01:13 AM   #7
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Default Re: carb swap issues

thanks, i think i have it figured out, i had to plug the main vacuum plug in the manifold, 3/8 man. vac. port to brake booster, 3/16'' manifold vac on carb to transmission, i am going to try using the timed vacuum port for the heater controls, and just see if they work. this has turned into quite the ordeal, the holley style carb and edelbrock that was on it is 100% different, had to get an aftermarket throttle cable as the stock one does almost a full loop to be the correct length, new cable and kickdown bracket, dual feed fuel line, and best of all no one stocks any of it here in town lol

the cam has a 286/294 adv. duration, never had any vacuum issues, but i have never tied andy of the vac systems togeather
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1974 3/4 ton gmc
450+HP 383

2005 GMC 2500HD Duramax Diesel- 452hp/962tq on P3's dyno

2015 Ford Expedition EL - Wife's rig
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