Rochester Quadrajet Woes

hey mister · Dec 6, 2024

So...for the most part I agree that QJ's are great carbs.
However, one aspect has been over looked...wear.
Specifically, throttle plate shaft/bore wear.
More specifically, the primary butterfly shaft bore.
If you can wiggle the primary shaft and see movement in the shaft, the shaft bore is worn out and that causes air leaks. Any degree of air leaking, especially around the primaries shaft will disrupt the air/fuel circuits. Start ups and idle will be a constant fight.

However, there is hope...
Install new bushings.
And I can do that.

So, I think I will start a new post about this cause I don't want to hijack this thread.

See ya there.

3 Ton · Dec 7, 2024

fast 99 said:
Be sure to replace the float, fiber only. Brass replacements do not work the same.

BS, very few carbs NEED fiber floats. Only a few Holleys NEED them black junkers. If your Quadrajunk is in a boat, then you might go fiber.
Amazon, auto box stores all sell chinese kits and parts, the lowest quality you can get.
Mikes Carb Parts has all American kits, and electric choke conversions and floats.

My question is have you removed the filter and ran it with out it in there? Might be in backwards, or plugged. The non American made ones tend to have clogs in them right form china.

BTW very few V8 four barrels that had fiber floats no longer exist.

fast 99 · Dec 7, 2024

3 Ton said:
BS, very few carbs NEED fiber floats.

Respectfully disagree, after doing emission work for 20+ years brass floats to not react the same or hold fuel at the same level. I was dealing with less than 1/2% co in most cases. If not familiar with emissions that isn't much. Not suggesting taking a carb apart because it has a brass float but there was a reason GM used fiber.

If you want to use brass go ahead.

edit

By the way for the most part folks on this forum are respectful. If you disagree I am very willing to discuss any of my posts. However, starting with a BS comment is a little overboard. There must be another way for you to express your thoughts.

Bextreme04 · Dec 9, 2024

3 Ton said:
BS, very few carbs NEED fiber floats. Only a few Holleys NEED them black junkers. If your Quadrajunk is in a boat, then you might go fiber.
Amazon, auto box stores all sell chinese kits and parts, the lowest quality you can get.
Mikes Carb Parts has all American kits, and electric choke conversions and floats.

My question is have you removed the filter and ran it with out it in there? Might be in backwards, or plugged. The non American made ones tend to have clogs in them right form china.

BTW very few V8 four barrels that had fiber floats no longer exist.

Its not that you NEED the fiber floats. What he is saying is that they react differently and if you don't know what you are doing it becomes a problem. The setup instructions for setting float height are designed for a fiber float. The brass floats are heavier and don't have the same buoyancy, so the fiber float setting that is called out for a specific setting will be very wrong for a brass float. It isn't a deal breaker, but it IS a problem if you aren't aware.

So, if you use brass floats, be aware that you need to set the float height LOWER, because the float will not rise as much for a given amount of fuel on a brass float as it did with a fiber float.

Sad Sack · Dec 9, 2024

It's the ol' air-fuel-spark conundrum.

I'm guessing...spark, since it wont run on ether and ether is usually sprayed straight into carb which eliminates the "air" factor since the air filter lid is removed. Take a spark plug out and ground against block and turn over, observe strength of spark.

Bextreme04 · Dec 9, 2024

Sad Sack said:
It's the ol' air-fuel-spark conundrum.

I'm guessing...spark, since it wont run on ether and ether is usually sprayed straight into carb which eliminates the "air" factor since the air filter lid is removed. Take a spark plug out and ground against block and turn over, observe strength of spark.

Its not "air" that you need. It's "compression". Yes.. you do need air, but if it is being allowed to come in to the engine at the wrong time, you won't get any compression and it won't matter how much fuel or spark you have. In these cases I usually pull the plugs and inspect them. Check for spark with a tester and check each cylinder for compression at the same time. If you have one or more cylinders showing you 100psi or less compression then the engine won't run and you have a mechanical issue. I had a case where the engine just randomly stopped running well. It would crank and not start. Ran a compression test and one cylinder had 0 PSI while all the rest were pretty close. Turned out I had a broken spring on the intake valve.

Slooptin · Dec 10, 2024

Here's a pretty good q jet resource for anyone interested

http://www.florida4x4.com/tech/quadrajet/qtune.pdf

Ajax19 · Dec 10, 2024

Brother who ever touched that thing in the past... my guess is plugs fouled from secondarys being open like that it's dumping fuel it needs to set it up right or your gonna have problems I think it's quadrajetparts or quadrajetpower should have parts you need

Chevrolado · Dec 10, 2024

My rebuild kit just showed up at my place and I'm really happy from the looks of what they put together for my specific carb... If you (original poster) are looking for a true rebuild, check these guys out. Looks to be a quality parts list and you give them your exact carb number to build from too. Seems like a great route.

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fast 99 · Dec 10, 2024

Does show a windowed needle and seat.

JBswth · Dec 12, 2024

KevinP said:
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.

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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.
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If your's is an automatic, I hope it wasn't towed with the drive wheels on the ground. That destroys automatic transmissions.

J. B.

JBswth · Dec 12, 2024

Slooptin said:
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

Rebuilt Carburetors | Guaranteed Carburetors

Rebuild kits usually don't come with links and such. I would try to grab one from a junk yard for use as a parts carb.

J. B.

Rochester Quadrajet Woes

hey mister

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3 Ton

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fast 99

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Bextreme04

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Sad Sack

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Bextreme04

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Slooptin

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Ajax19

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Chevrolado

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fast 99

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JBswth

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