Thanks for the info it’s much appreciated. I’ll check it out!
Quadrajet or Aftermarket?
- Thread starter TheSaint
- Start date
Mark,Jack the problem with the pre-1975 carbs is that the metering rods are a little longer than the post 1975 ones. They are not interchangeable. Even with eight years of production, they are much harder to find than the six years of the later ones. Seems odd but that is what I have found to be true. That said, I like to use the later Q-jets simply for the APT, and the electric chokes. The electric choke can be back fitted easily on the hot air choke models. But the old intake manifold choke stove coil type are totally impossible to convert. I have tried and failed. It's funny now, but I used to trip over Q-jets at swap meets years ago. The lowest I paid was three dollars for one. So I stripped them down for parts and I have a large selection of rods and jets to play with. You can get jet sets on Fleabay easily, but metering rods are tough to find and expensive.
I found the carb # in my notes. which indicates #17056221.They claim it's for a '76-'77 Chev/ GMC truck 454. Somewhere I thought I saw that it was for a 400 sbc. It also indicates that it's an electric choke carb, which it has.. Now to find notes on what jets, metering rods and hangers it uses.
I guess being a slightly later carb is a good thing, huh?
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Yes Jack, I would prefer that model over the earlier ones. Have you opened it and recorded the rods and jets? Even though I am the world's worst person for writing things down, I actually have recorded the info on most of my 'good' factory carbs that I use. So a dead stock carb's specs can be used for a base line when modifying. When in doubt I refer to this site for the factory parts and specs. You would go to the Chevy section and look up your year and carb number. That tells you what was in it when new. Then you look up what came on the engine you are using. Or something as close as you can get. This site is a gold mine of info and I swear by it. https://www.newagemetal.com/ You should have a #77 jet [BIG!] and a #45 metering rod. If you still have the #77 jets there should be NO flat spot. A 350 would be drowning in fuel.
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Mark,
As far as I can tell, it should be a dead stock carb, with baseline jets, metering rods, hangers, etc. I figured it would be on the fat side being it's for a larger displacement engine. Running headers and a mild street cam would probably balance it out somewhat.
I'll look a little further for the specs of this carb.
Of course, I've opened this carb up and overhauled it... plus re-bushed the primary throttle shaft.
As far as I can tell, it should be a dead stock carb, with baseline jets, metering rods, hangers, etc. I figured it would be on the fat side being it's for a larger displacement engine. Running headers and a mild street cam would probably balance it out somewhat.
I'll look a little further for the specs of this carb.
Of course, I've opened this carb up and overhauled it... plus re-bushed the primary throttle shaft.
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Jack could the flat spot actually be a bog? That carb in stock form is probably way too rich for any 350. I think the biggest jet set I ever came across was #75s and they were in a Pontiac 455. I did use #75s on a 1974 Corvette I was involved with. Someone had stuffed a WAY too crazy cam into an otherwise stock 350 and plopped a huge Scummit carb on top. No way to change cams so I replaced the Scummit carb with an 80's Suburban Q-jet carb. I had to drill the idle ports just to get it to stay running. Even then it needed 1000 rpm to idle at all. The #75 jets worked great but the car was still a pig because of the dead rear gears. It's like when adjusting the secondary side. Everyone thinks you need to loosen the secondary flap spring and make it open faster. That results in an over rich bog and then the 'Quadra-bog' name gets assigned. The trick is to TIGHTEN the spring so the flap opens later. You want the primaries screaming before the secondaries even think about opening. THEN you have a smooth transition and make gobs of power.
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You guys really go into detail on these issues which is awesome, but leaves a guy like me a bit confused. lol
Don't be. The Q-jet is the easiest carb to work with once you understand how it operates. Get the Doug Roe book 'Rochester Carburetors'. It is my bible of Q-jets. There are other Q-jet books but they are more performance orientated. The Roe book concentrates on theory and purpose. It covers from one barrels to the CCC Q-jet carbs. The biggest thing I learned was that the carb that came on the engine from the factory is the BEST carb for that engine. But it gets dirty. A simple cleaning [without messing with it] is all that is needed to keep it working perfect. But if necessary, it can be modified right up to racing form. ---------------------------------------------------------------------------------------------------------------------------------
I bought mine at NAPA last year for about that with tax. It was the last one in store, and so dusty I had to shake the packaging outside.
Mark,
I don't think it's a bog. Once it gets by the "flat spot" which is a sudden blip, it accelerates fine. It really doesn't fall on it's face. Aside from that, it runs quite well. The idle might be a tad high, but once it warms up it idles around 1000 rpm. maybe 900 rpm and gets good strong, steady vacuum.
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