Quadrajet or Holly 650

[cottonme173]

This is on a '77 GMC C2500. Stock 4 speed, 4.11 Gear. I am not racing, just running on the street.

SO, initially I am having issues at full throttle. When running I can get trough second and third, but when I go into fourth and hit the gas my truck stutters and fails to speed up. If I gently push the gas it seems to keep up. Not that I floor it a lot, but I should be able to punch it.

I know very little about the Qjet's so I am starting very low there.

I am going to pull the truck in for the winter and go through both gas tanks, replace lines, replace the mechanical fuel pump, so this MAY actually solve my issue. I have the option of getting and rebuilding a Holly 650 to put on the stock intake. Will this even be worth it? Will there be a performance (MPG?) increase doing this?

I hope there are not a hundred other threads on this ( I tried searching and didn't find any).

I would love your input on this!

[meatwagon83]

On a stockish engine you can't go wrong with a quadrajet! Get yourself a book and rebuild it right, I've had holley carbs and edelbrock carbs on my truck and I keep coming back to the quadrajet, decent power and the best milage this side of fuel injection

[cottonme173]

Thank's for the input! When I first got the truck a few years ago I had a tune up done, but I was only getting a little over 6mpg!! I think I have a delivery issue though. That's why I am going through and replacing everything. Not sure what MPG I should expect with the 454, but that seemed low. I will find a rebuild kit for the Qjet and stick with that if that is the best thing for now.

[cottonme173]

Upon research......I guess that's on the high side of what I should expect....SMH...

Anyone need a 454....

[meatwagon83]

I rebuilt mine with a small bump in compression, a small cam (comp he260) headers and a performer intake, with a fresh quadrajet, 10 around town, 12 on the open road, no overdrive, 3.73 gears, and that is in a crew cab dually, when I got the truck it was stock with an edelbrock 750 on it and it got 9

[truckin 79]

I would go with the Holley if it were mine. The holley is easier to adjust float level and idle mixture screws on the side. The q-jet has idle screws in the front and if you get junk in carb you have to take half the carb apart to clear. I have a q-jet on Trans Am and Truck, it took me a lot of tinkering to get the q-jet on TA to start with just a flick of the key. The q-jet on truck is fighting me though and needs some more fine tuning, I just rebuilt q-jet so trying to stick with it for now. I might switch to a Holley on truck with vacuum secondaries and it should get about the same gas mileage as q-jet. In the end both carbs are good but q-jets a bit more fickle IMO.

[geezer#99]

Originally Posted by truckin 79

I would go with the Holley if it were mine. The holley is easier to adjust float level and idle mixture screws on the side. The q-jet has idle screws in the front and if you get junk in carb you have to take half the carb apart to clear. I have a q-jet on Trans Am and Truck, it took me a lot of tinkering to get the q-jet on TA to start with just a flick of the key. The q-jet on truck is fighting me though and needs some more fine tuning, I just rebuilt q-jet so trying to stick with it for now. I might switch to a Holley on truck with vacuum secondaries and it should get about the same gas mileage as q-jet. In the end both carbs are good but q-jets a bit more fickle IMO.

A lot of tuning and lack of mileage is related to a slow timing curve. Especially at elevation.
What's your timing like truckin?