Rochester Quadrajet Woes

Thanks for the add. I have a '76 C20 with a 350ci engine / TH350 trans that I bought about three months ago. It was running great until a few weeks back when it died in traffic and I had to have it towed home. At first glance it appeared to be a fuel delivery issue, so I replaced the in-carb fuel filter on my Rochester Quadrajet. That's when I noticed that the previous owner had eliminated the vacuum break rod (the piece of linkage that opens the secondaries the correct way) and then he pinned open the secondaries by using a cable tie going to a hardline from the attachment point for the rod in question. I have attached an image of what he did, but I'll warn you that it's a shady sight. It ran OK for a few days with the new fuel filter, but then it died again in my neighborhood and now it won't start at all. It will crank, but it will never fire up (even on ether). My question is this; would it be better to try to rebuild the Rochester Quadrajet that has been monkeyed with (it may or may not even be an original unit), to buy a remanufactured Autoline Rochester Quadrajet from RockAuto, or to upgrade to a different carb setup altogether? Also, are there any aftermarket carbs that will work with my existing intake manifold? I know I'd need to run an inline fuel filter if I change carbs, but other than that I'm trying to keep things as stock and as cost effective as possible, as we use this truck for truck things regularly. We could really use it back up and running ASAP. Thank you in advance for any advice, and Merry Christmas.



PS: Don't worry. I have period correct wheels and hubcaps ready to go on it. I just have to keep my priorities in check at the moment.

IMO, it might be worth it to rebuild as the kits are pretty cheap. I just ordered an ACDelco rebuild kit off amazon for like $30. I also try and pick up old q jets off marketplace or from the junkyard when they pop up for cheap just to have parts or spares around if I ever need them. If you're thinking about buying reman, check out guaranteed carburetor out of Florida. I've heard good things from people I know who've used them

Thanks. I have a rebuild kit and I have considered going that route. I'll check out the company you mentioned. I may buy a reman unit just to get it moving again quickly, and then rebuild the one that that is currently installed as a backup if I can determine that it is a real period-correct Q-jet. I like things to be as close to original as possible. I'm just not an aftermarket / performance guy. I feel like you change one thing and then you end up having to mess with everything.

I'm thinking it should at least fire on ether regardless of carb issues. Have you checked for spark at the plugs?

Whens the last time its gotten plugs wires and a coil?
Failing to run on ether is the red flag, its not a carb issue i dont believe

Sorry, I should have clarified that there are multiple issues at going on at the moment, but the pinned open secondaries and missing linkage really bugged me. I hate backyard “quick fix” nonsense like that. I figure I might as well get the carb stuff sorted properly too while I’m chasing down my spark issue.

When I had crank no fire issues with my truck, it was always a loose wire or a short, either under the hood or on the starter. If your engine won't fire at all, it's almost certainly electrical.

My thinking was the same as you on the Quadrajet. I looked at carburetor options, and almost all of them required a new intake, and had a different fuel inlet setup. I was trying to go with something original and reliable, rebuilt by somebody competent.

I ended up going with a JET Performance Stage 1. It's a later model Quadrajet than my original, but it was similar enough that I could be sure I hooked up everything that needed hooking up, and it ran out of the box. In my case, the new harness I installed had a wire (and a fuse) for the electric choke, but that wouldn't be too hard to deal with if that hadn't been true. If you need help sorting that out, I'm sure someone can help, but I'll set that aside for now.

I'm going to rebuild my original Quadrajet one of these days, and convert it to electric choke. The original divorced choke I had was not remotely working, and the manual choke conversion it had was not working either. I still haven't figured out why the choke butterfly is just permantly fixed the open position, and nothing short of a damaging amount of force is going to budge it. In the meantime, I have the Stage 1 running pretty well. It still has some wrinkles I need to iron out, but it's basically reliable to get me from A to B now, and it starts in cold weather. Everything else is a later problem.

Good luck!

Has multiple issues. Check for spark and plug condition.

On that style carb choke thermostat is heated by the intake. There should be a operating heat riser. Most times on older vehicles there is some restriction to the crossover passage or stuck heat riser. Those need to be checked at some point. Will not cause a no start.

Secondary air valve [wired open] is there to slow the air entering to allow the fuel to "catch up". Rigged like that as soon as throttle is advanced enough to open secondaries engine will fall on it's face.

Missing rods need to be located. Appears pull off and it's rod are also gone. If those parts can't be located carb can not be overhauled. if that's the case later q jets have an electric preheat stat and might be an option.

Get it running again first. Then deal with the carb after you've sorted out the other issues. Reason is you change x y and z at the same time. Now if it doesn't run right well x must be bad so you spend a Day jacking with that,nope well z must be bad another day wasted,well it's gotta be y. Nope it was r.

fast 99 said:

Has multiple issues. Check for spark and plug condition.

On that style carb choke thermostat is heated by the intake. There should be a operating heat riser. Most times on older vehicles there is some restriction to the crossover passage or stuck heat riser. Those need to be checked at some point. Will not cause a no start.

Secondary air valve [wired open] is there to slow the air entering to allow the fuel to "catch up". Rigged like that as soon as throttle is advanced enough to open secondaries engine will fall on it's face.

Missing rods need to be located. Appears pull off and it's rod are also gone. If those parts can't be located carb can not be overhauled. if that's the case later q jets have an electric preheat stat and might be an option.

Click to expand...

This is a pretty good description of what should be happening, but I'll add a few caveats.

Early quadrajets like this one only had one pull off on the front. That still appears to be present. The pull off actually keeps the rod from being able to extend when a high engine vacuum is present and has a measured leak to release the vacuum slowly when the vacuum disappears(during full throttle). This helps limit the stumble from the blades slamming open immediately.

Here's a pic of a complete original linkage setup for that era quadrajet:


It also appears that someone had it apart before and did not reassemble it correctly. It looks like maybe they put the secondary lockout lever on there backwards, or at least not correctly riding on the high idle cam. I have marked up the OP's original pic to show where the rod should be and also the end of the lockout rod that should actually be below the choke cam. The other end of the circled rod locks out secondary throttle linkage from being able to move when the choke is engaged. You can see the end of the rod holding the pin on the end of the secondary linkage in the pic above as it is supposed to be.

Also, notice the black ziptie on the vacuum port... that is locking out your choke. Cold starts will be tough. I would recommend you buy the correct rod and cut off those zip ties. It's possible that the choke thermostat is bad. If it is, the rod going down towards the manifold will move freely, otherwise gravity and airflow will have that linkage being pulled up and the choke will be randomly opening and closing. There are a few conversion kids to make that either manual or electric if the current thermostat is busted.

Here is the correct linkage(I think)... $8.99
https://quadrajetpower.com/new-vacuum-brake-pull-off-linkage/

New choke thermostat(mounts under that metal cover).. $34.99
https://quadrajetpower.com/divorced-choke-thermostat-chevy-350-71-78/

Great advice. Thank you so much!!!

Take a close look at the throttle linkage side of the carb and get the Quadrajet number. This tells you which carb you have (original or later), and you will need it to get the right rebuild kit.

For example, my original 1975 Quadrajet is 7045583, which is an older version, but I am currently using an 80’s 17080213 that I have changed to an electric choke.

If you find a cheap rebuild kit ($25 was mentioned) it may not work very well. Base gasket and other details changed over the years, and you need a kit that really matches your carburetor number and truck characteristics. For example, the kit I got from Cliff Ruggles included calibration of jets and rods for use with better flowing aluminum heads, it has an accelerator pump with ethanol-resistant seal, all new gaskets, various step-up springs to tweak the lean/ rich rod transition, etc.

Thanks. I'll look into this. I bought a rebuild kit already, but I'd hate to find that out once everything has already been disassembled! Since you have already completed the process of changing to electric choke, is there anything that needs to be blocked off or redone vacuum-wise when switching to an electric choke version, or do just need to wire up the electric choke to a ground plus a key-on power wire and then install everything else normally? I thought about upgrading to one with electric choke, but I don't want to make things worse by getting it wrong.

Be sure to replace the float, fiber only. Brass replacements do not work the same.

Got it. I've heard about that. Thanks!