best carburetor for a ‘79 GMC C7000

[wbmoore]

Just bought a 1979 GMC C7000. It has a 366 big block. Needs a new carburetor. I’m wondering what would be the most reliable replacement. The truck will not be used very often, I’ll run it every month to keep it exercised but it will be driven very few miles. It’s a Forest Service crew truck with water pumps to be used in case of emergency while waiting for the Real Firefighters to arrive. The 366 runs one of the pumps off the PTO.

Carburetor does not need to make high horsepower. Most important is Always Starting Easily and then Run Smoothly after sitting for a month. There will be a few 30˚ days and even more 110˚ days.

Truck now has a very old Holley.

Thanks for any input.

[franken]

It might help to know the type of carb. 2 or 4 barrel?
Sadly, if you don't keep fuel flowing through the fuel system, ethanol in the gas will cause problems. I haven't checked but this site supposedly lists places w/ good gas. https://www.pure-gas.org
Or a stabilizer.

[sweetk30]

most i have readis 500 cfm or under in 4 brl size to keep the flow good and fuel speed up and no kill it from slow down of the bigger carbs .

i have read if ditching the factory stuff do a rpm limited ignition setup and bump it 200-400 rpm over the 3,400 rpm stock to get you a little more pull over the stock setup .

[wbmoore]

This is the carbahooter that is on it now.

[franken]

Ok, square bore vac secondary. Guessing it's a 600 or so. I'd probably throw a kit at it unless it's leaking from the throttle shafts. It isn't that tough.
Why spend $400 for a similar carb?

[wbmoore]

I’m told these are overly complicated and un-reliable carburetors. I’m looking for a carburetor that is simple and reliable enough to sit for a month and then just start and run. I’m looking for recommendations for that carb.

[jumpsoffrock]

Honest to god you could risk it suffocating on a two barrel carb, and get a carb adapter and put a Rochester dual jet. You'd be going from a larger air volume four barrel to a two barrel.

Quite frankly I have one on my Chevy 327 small block and it spends a lot of down time--on the only rebuild I gave it in 2014, mind you--and it drinks the cheapest ARCO I can find; no leaks, and to my complete surprise it starts and runs fine.
My choke is inoperable and even on a 40ºF day in winter after not running for a few weeks it will start almost immediately if you hold the gas pedal just right to simulate a choked setting(more fuel less air).

If I let it sit more than a month, It will allow the fuel in the carb bowl to evaporate away making for longer starts(15-20 seconds of cranking at the most) but as long as it's started once every two or three weeks it'll start and run like a champ.

If you were running a 454 I might shy away from a two barrel, but for your non-high-RPM needs and the engine is only a 366, you could spend a little money and try it.

Those Rochester Dual Jet's are very simple and tried and true.

[semn49]

Personally, I would throw that (or any other Hhhholley) carb to a drag racer!
Find yourself a Rochester Quadra-jet. If you have to, buy a spacer/adapter.
Then as previously posted buy gas without ethanol.

I'll probably get scolded for saying that about Holley carbs, but in my experience, I've always had good luck with Rochester carbs.

[1976gmc20]

Not exactly the same thing, but my 76 had a Holley on a 350. It did great on the highway, but did not tolerate being driven slowly around in the woods. It would flood and barf gas all over the top of the engine!

I got a Qjet from a junkyard and had a neighbor rebuild it for me. Worked fine after that.

Nice truck, BTW

one of the pumps

So does it also have a small engine pump? The PTO pumps don't work very well for "pump and roll" operations. But maybe you're just doing stationary structure protection. I don't know your experience but let me know if you have any wildland firefighting questions.

[geezer#99]

Originally Posted by wbmoore

I’m told these are overly complicated and un-reliable carburetors. I’m looking for a carburetor that is simple and reliable enough to sit for a month and then just start and run. I’m looking for recommendations for that carb.

Why change the carb?
If it needs a rebuild do that.
If you want it to start once a month just plumb an electric fuel pump into the fuel line close to the tank. Set it up with an on/off toggle switch. Turn it on for 30 seconds, close the choke, give it a couple pumps and fire it up. Shut off the electric pump until next month.
You don’t even need to rebuild it first. Try a pump first.

Here’s a carter that has a max pressure of 4 psi. Perfect for starting.


https://www.summitracing.com/parts/crt-p4389?rrec=true

[jumpsoffrock]

Originally Posted by semn49

Personally, I would throw that (or any other Hhhholley) carb to a drag racer!
Find yourself a Rochester Quadra-jet. If you have to, buy a spacer/adapter.
Then as previously posted buy gas without ethanol.

I'll probably get scolded for saying that about Holley carbs, but in my experience, I've always had good luck with Rochester carbs.

If he's looking to replace something complex with something simple I'd think that a Q-jet would be essentially the same level of complexity to what he has.
I'm also a Q-jet fan but those are for performance, he just needs it to start and run. The Q-jet has many adjustments that really aren't necessary unless you want max performance.(depending on what year the Q-jet was produced)

[Tom]

The holley on there is no more complicated then any other vac secondary 4bbl IMO.

A Qjet is very complicated with all the adjustments possible. But it would give the most reliable performance once set correctly.

No matter what, how fast the fuel in your area degrades will be the biggest factor in reliability from sitting.

[franken]

Originally Posted by wbmoore

I’m told these are overly complicated and un-reliable carburetors. I’m looking for a carburetor that is simple and reliable enough to sit for a month and then just start and run. I’m looking for recommendations for that carb.

The same carb has been on it for 40 years. How unreliable do you figure it is?
Crap gas will be the issue, not the carb.
Google ethanol.

[wbmoore]

1976GMC20....the auxiliary pump is driven by a Wisconsin TJD. The PO (a pro auto mechanic) lightly rebuilt it. Ran on the bench but didn’t when he reinstalled it on the truck. The truck has been sitting so I am working on the systems to put them right. Main pump does work. The biggest problem is the carb......won’t start after six hours without being primed. For now, maybe the fuel pump mentioned above would be a quick fix.
Truck will be stationary for the most part.
Don’t know enough about wildland fire fighting to even ask questions.
I was hoping for a consensus on a replacement carb....too many things to do to spend time rebuilding a carburetor.
Thanks for the input.

[jumpsoffrock]

I apologize for having 5 guys give you five varying answers, but I contend that if you're looking to go less complicated, subtracting two of the barrels is taking some out complication of it.

I cannot even find a carb rebuild kit online because I can't ID that carb from my chair.
Rochester dual jets were widely used and a carb kit can be found easily; might have to go online for an adapter to make fit on your manifold.

Of course every person here thinks they are correct, however I stand by that the only answer that truly makes your engine running a physically less complex task is switching to a very common and well understood two barrel: Rochester 2G







EDIT: I'd also like to point out that ANY new carb--including my idea--will require the fabrication of some type of throttle linkage. You really should consider a rebuild of your current unit unless you want to figure out how to fab linkages somewhere in the mountains.

[1976gmc20]

Don’t know enough about wildland fire fighting to even ask questions.

It would be good if you could somehow take a Basic Wildland course. I wish there was a quickie version for rural residents (maybe one day instead of two and a half).

For rural structure protection, fuel mitigation and "defensible space" are your friends.

[CABLESCUM]

Seriously:

If you don’t want to mess with it, snatch that carb off and take it to a reputable carb guy, put it back on then drive it to him and have him tune it. Then repeat every 10 years.

Holleys are not difficult at all. I rebuilt my first one when I was 14 lol

[Bigdually]

I scoured the internet to find an answer to the SAME question, and I found several farm sites where grain haulers and farmers all had a consensus, the tried and true 1406 Edelbrock. I found a 1906 locally, the AVS2 updated model, for the same price as the old model. It's the readily available carb on most auto parts store shelves and they're dead simple to adjust. The electric choke works flawlessly and it holds it's tune perfectly. I cannot say enough good things about the positive gains I saw going from the same Holley garbage governed carb you have to the Edelbrock. You will want a 1/2" phenolic or composite wood spacer between the carb and the intake to help kill heat issues. The one (and only in my opinion) downfall to the Edelbrock is that the float bowls will boil dry easily it seems, and today's ethanol gas boils faster so you want it as cool as possible.

[sweetk30]

i have the 500cfm man choke std edelbrock waiting for my 366 in the GMC 7000 dump . i did get a spacer and also a pertronix upgraded ignition mod for the dist to give me a rev limiter i can set . and few old timers i talk to and stories here all say go to around 3800 rpm limit . 1 guy said the old fire tanker he drove if he just had 200 more rpm he would of been golden . . .

[wbmoore]

DING DING DING....geezer#99 gets the prize. Had an electric pump on the shelf, cobbled it in and BINGO....after sitting for twelve hours, it started....something it hasn’t done for a long time. Now I’ll wait a week and see if that happens again. THANKS for the thought geezer.

Bigdually, sweetk30..... I was thinking Edelbrock too... 1405 manual choke. Good to know the farmers use them.

Jumpsoffrock....looking at a GMC manual...some of these things came with a 2G on the Big Blocks.

1976gmc20....if I find a class, I WILL take it.

The seller told me it was a 366 but the glovebox tag says 427...but I guess that doesn’t really matter.

Thanks for all the positive input.

[1976gmc20]

1976gmc20....if I find a class, I WILL take it.

The trick will be getting a seat unless you're signed up to be a fire fighter.

If you know somebody them maybe they would loan you an instruction binder to read.
Might be some stuff online also.

A little bit of knowledge can make your efforts more effective and might save your life.