First real drive! Not tragic but not good. I think I need carb advice.

[Chris64]

So I've been checking off items to make this thing drivable and nothing's been easy.

Lights; I had no lights and no single problem. A few cut wires, a few chewed wires, a few bad bulbs and a few bad connectors and even some bad bulb sockets. I know have full lights (outside) blinkers, brakes and even reverse. Each one on each side was a fight.

Suspension; I had one broken shock and no others and a leaking steering stabilizer. I now have 4 new shocks and I have a steering stabilizer (but I'm waiting for that since I might need to do some steering surgery).

Brake fixes; new soft lines. I'll probably be replacing them for longer lines and I'm wondering if I should just replace the master cylinder because it's 50 years old. It seems to be fine.

ANYWAY, My son and I decided to take it for it's maiden voyage to get gas...it's on fumes on both tanks. The engine takes a really long time to warm up, but even warm it has a dead spot in the first part of the throttle. If I can get past that it seems to rev OK but this is an automatic so that's not really doable driving. So it stalls constantly. We aborted about 1000' out because the steering was super sloppy and I hadn't done more than a simple visual on it. It became very tricky when I had to turn around and go up hill. I couldn't accelerate without it stalling. It's idling was high enough that I was able to crawl home with just that.

So long story short; brakes seem good, steering is super loose (30 degrees of nothing between left and right) and the steering wheel is at 90 degrees (hopefully the last owner just installed it that way.

But none of that matters if the engine can't reliably idle or rev so that's my focus for now.

The stock carb and air-cleaner is what I have (for a 350, quadra jet I think they call it). I've been advised to get an Edlebrock AVS2 but I'd like to hear what others recommend. Is there a good carb/aircleaner combo that can bolt right on to stock? I've never dealt with carbs on a car.

I have not changed the plugs, checked compression, checked the timing or really done any engine work at all. I just checked the oil which looked good (the previous guy said he changed it). It was running (sorta) so I didn't want to mess with it. It sounds like all cylinders are firing but I could be wrong.

Or should I try to get the quadrajet working?

 

[fast 99]

Before thinking about buying parts some diagnosis first. Check over the tune up, good plugs not fouled, timing, both advances, inspect wires, cap, ect. Check fuel pressure and volume. If possible check vacuum.

If it does have a q jet with appreciable age likely float is heavy and needs o haul. Some will disagree but the original q jet is the best compromise for economy and driveability on a GM. If you are intent on replacing the carb keep in mind they are generic and may require jet changes or other adjustments. Eldebrock/Carters are decent carbs and can be made to work fine. Just they aren't as bolt on as people assume.

 

[EvilGenius]

I went with a different carb for my 350. After some research I decided to go with a summit carb that is a clone of an old holley. It was around $400 and worked great out of the box. I went with it over the standard holley and edelbrock options due to price and I personally don't like the holley front/rear bowl design that leaks everywhere if you want to make a jet change.

Here it is if you decide to look into a replacement https://www.summitracing.com/parts/sum-m08600vs

 

[Ricko1966]

My take on Quadrajet vs. Other carbs. There are dozens if not hundreds of variations of quadrajets, changes were made to tailor them to the engine combination they go on. The standard go to replacement carbs have a very generic base tune,Qjet there will be a different model for standard tran vs. Automatic,AC vs. no AC etc.Not so with the generic replacements. I'd rebuild or have rebuilt my original or correct number Qjet. One that was designed by people way smarter than us to run,winter,summer,start hot,start cold,decent mpg,not foul plugs. The whole package. There's a reason GM didn't use a one size fits all carbureator,and cost savings wasn't the reason. No matter what carb you go with,checking compression and making sure ignition works correctly is first. Lots of good carbs get blamed for bad advance mechanisms etc. I read all of your post should have done that instead of a quick skim to begin with. Not able to accelerate without killing it, first thing I'd check is accelerator pump shot. Hold the choke open with one hand open the throttle with the other you should get 2 squirts like a squirt gun shot,1 down each primary barrel. ( ENGINE OFF)

 

[Chris64]

Great tips. While I really like the idea of buying a new thing that will just make everything better...nothing works that way.

I guess I need to buy some tools (compression test & timing light). The sparkplugs and wires are another challenge. The only thing the previous owner did "upgrade" was the headers which do a two-one thing. They run straight out from the engine which makes them dangerously close to all the plug wires. He wrapped one of the headers in that heat wrap stuff but not the other and he put little heat shield covers on the plugs and wires. It should probably all be redone and I wonder if it would be worth getting different headers that follow a more stock routing. Removing these headers may be another nightmare based on the rust.

Strange question; I needed to work on/replace the front fenders and inner wheel covers and hood. Is it reasonable to remove this stuff to work on the engine? So far working in the engine bay is a real PITA because how high it is.

 

[77Dmax]

You probably have a vacuum leak somewhere.

 

[Chris64]

You probably have a vacuum leak somewhere.

In reading about how to tune the quadrajet - I saw this same comment. I have a vacuum hose hanging on my passenger floor...Any idea where this goes? I assume it's part of the AC. Is that the same vacuum?

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[75gmck25]

Your truck is nearly identical to my ‘75 GMC K25, except that in ‘75 they made HEI ignition standard and tweaked a few other minor things.

The ‘74 Quadrajet is one of the older designs, since the truck carburetors got upgraded later than cars. It will work fine if rebuilt properly, but later carburetors have an externally adjustable APT, and some other improvements. A good Quadrajet rebuild is not cheap, which is why many move to a newer model like the Edelbrock AVS2 instead.

I have spent a lot of time and money tightening up my steering and front end. Start out with replacing the tie rod ends, the drag link, and the rag joint. This will not take out all the play, but it will help a lot. You can also work on adjusting the play in the steering box, but read a lot about the process first, and don’t get it too tight.

You can remove fenders and inner fenders to make working on the engine easier. However, you might first try just removing the hood. That allows you to use a short stool to step up and sit on the fender, with your feet in the engine compartment, and that shortens the reach quite a lot.

 

[75gmck25]

I believe that vacuum hose is for the HVAC recirculate function. It has a T because it connects to a vacuum motor in the cowl, and another one in the passenger kick panel. I think the rubber fitting is probably around the line that goes up to the cowl.

There is a round vacuum canister next to the A/C plenum under the hood. It will have one line running over to the intake manifold, connected to manifold vacuum. It has a 2nd line (usually a plastic hard line) that runs through the firewall and over to the HVAC dash control.

 

[77Dmax]

I think your vacuum leak is under the hood. Check all your hoses and spray some carb cleaner while it's running.

 

[Chris64]

I think your vacuum leak is under the hood. Check all your hoses and spray some carb cleaner while it's running.

Yeah - there is a hose coming from the carb that isn't going anywhere. I thought it was from the line on the intake that has the heat hose from the header (which I don't have) but I think it may go to the carb. I'll need to remove the air cleaner to follow it. I'll have to do that tomorrow.

 

[75gmck25]

The air cleaner has a thermostatic valve in the snout to control heated air, and it’s connected to vacuum at the carburetor. No reason to have that hose if the heat stove and tube to the air cleaner is not mounted on the headers.

If your carburetor is like my ‘75, it has an extra (larger diameter) vacuum port on the front and it connects to the vent on the emissions vapor canister. For large diameter vacuum connections, my newer Quadrajet only has one 3/8” PCV port on the front and a large threaded brake booster port on the back.

You probably still have a hot air choke, so there are some extra small ports that look like vacuum ports. They are not really vacuum ports, but are used to pull air through and heat the choke mechanism, so they can be capped to simplify troubleshooting your vacuum leaks. If they converted to electric choke they should have capped the extra connections.

 

[fast 99]

A couple pictures would help. Obviously with headers the heat riser valve is gone. That effects intake preheat and choke operation. Hard to help with diagnosis not knowing what your working with.

 

[Chris64]

OK - here's some pics of what I'm working with. I do see a little diaphragm looking thing off the distributor with nothing connected so that's probably wrong.

I'll see what I can find in the PDF service manuals but it seems like you guys will spot things I wouldn't even think of.

First pic - the rusty engine - red circle is a stray hose.

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Second pic - diaphragm should be connected?

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Last pic - headers keep-worthy? I wanted to take them off just to at least wire brush off the rust. Any suggestions for wire management? I could probably steel wool that back to shiny metal.

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[Ricko1966]

We need a pic with the air cleaner off. Need to see where the stray hose connects to the carbureator. In your second Pic that is the can for the vacuum advance,connect it to manifold vacuum. You still need to check accelerator pump shot. Put a piece of hose on the vacuum advance and suck on it does the diaphragm move you can feel the Plunger on the back with your finger. Does it hold vacuum or do you have to keep drawing on it?