The Stovebolt Site Forums The Shop Area Engine Shop Carb advice for 283

Howdy all,
I just purchased a '71 Chevy K10. It has a '64 283 in it, but I've been told the heads and intake are off a 305. I believe it because it has the EGR valve, etc., on the intake. I haven't gotten the truck back home yet to get some casting numbers, but this is what the guy told me. It needs a new carburetor, so with this set-up (it also has headers by the way), would a 570 cfm holley be too much carburetor? Thanks a lot,
Si

No.

cm

570 CFM would be OK. I wouldn't go any bigger.

Thank you much.

A 570 should be fine. But it might not just bolt on to your intake. Might need an adaptor.

NuthinFancy78,If the original intake is still on the engine,you will need the aluminum billet adapter to bolt your new carbutator,unless you are going with the original Rochester Quadrajet. Someone can correct me if I am wrong. I just replaced the carb,on my 350SB,and I had a AirGap aluminum intake,and I didn't need the adapter.I went with the Edelbrock 600cfm,the engine I have is a 4bolt main,with a mild cam. Good Luck.

My 283 is bored over to about 302, and even then a 650cfm is to much (seems to cause backfire). 570 will surely be a good choice

Is it back firing through the carb? Like a cough or sneeze? Is it snorting a flame through the carb? Or is it giving a loud bang through the exhaust?

No, it doesn't backfire through the carb or through the exhaust. I don't think I have a timing issue, other than the points need fine tuned. It floods terribly to the point where you can't get it back running before the battery dies and fouls plugs like nobody's business. I've "rebuilt" several of these Quadrajets, and have yet to find one that will actually "rebuild." That is why I was considering switching to a holley. Thanks for the adapter tip guys, I almost forgot about having to do that on my '78 when I switched to an edelbrock. Thanks for all the help.

At idle, look into the carb air horn. If fuel is bleeding into the carb, the float level is high. The needle seat could also cause this problem.

What sort of problems are you having with building a QuadraJet? I've been working on them since the mid-1960's when they were first introduced, and unless there's been severe corrosion or other damage to the castings, they're one of the best-designed carburetors on the market. Of course, it's necessary to use the correct part number for the application, and follow the adjustment procedures exactly, but that's true for any carburetor regardless of manufacturer. Most problems with carburetor rebuilding end up being operator error, not the fault of the carburetor.
Jerry

It could very well be operator error, I'm no master mechanic. I've rebuilt other carburetors without problems, though. Usually though, some piece is too corroded or damaged to repair like you mentioned Hotrod or some part is broken that I can't find a replacement part for. I just seem to be jinxed by Quadrajets, they run excellent for me until they need rebuilt, and then I can never get them right again. I have different problems with different carburetors. One such example was fuel pouring out the top of the carburetor. I believe this was because the plastic piece that sits on top the float assembly was broken, and the local parts stores couldn't find a new one. I'm fairly certain I had the float level set right, so I don't think it was that. Any advice that would enlighten me to the finer points of these beasts would be very welcome. Thanks for the help everybody.

One thing that I've found about working on them is that it's necessary to replace the float every time I rebuild one. Those plastic floats have a nasty habit of soaking up fuel and getting so heavy they can't produce enough lift to effectively shut off the incoming pressure. Another trouble spot is the riveted-in plugs at the bottom of the float chamber. They get loose and leak, emptying the float chamber as the vehicle sits overnight. I like to peen the plugs tight with a small ball-peen hammer, then use a fuel-resistant epoxy over them to assure there's no problem with future leaks. The plugs are supposed to be in a "dry" area, so if the leaks can be stopped, the epoxy doesn't deteriorate from being submerged in gasoline. That plastic cover over the float pivot could have been scavenged from a junk carburetor, but it's not likely an aftermarket supplier would be able to find a replacement. I don't think I've ever seen a broken one, in 40-something years of fixing Q-jets.
Jerry

With absolutely no offense meant:

The Q-Jet is one of the very finest carburetors to be built anywhere in the world at any price and any time period!

If you are having issues, I would highly suggest the book on Rochester Quadrajets by Cliff Ruggles. Of all of the carburetor books I have read since 1959, this is by far the most "novice friendly"; and probably the second best of any carburetor book (the first requires some knowledge of differential equations)!!! You might take this recommendation with a "grain of salt" as Cliff is a good friend; but he has done a fabulous job.

As far as the flooding is concerning: the three major causes of Q-Jet flooding are:

(A) defective plastic float (as Jerry said, this is an automatic replace EVERY TIME! Don't even think of trying to test one).

(B) too much fuel pressure. The Q-Jet doesn't like fuel pressure. Most A/M pumps will overload the float buoyancy.

(C) too large an orifice in the fuel valve. Rochester made many different ofifices. (And the A/M has an even larger one). Get a quality kit designed specifically for your carburetor (not a generic "one size doesn't fit any") that has the proper fuel valve.

Yes, the early Q-Jet had "teething" problems; but nowhere near so many as the 4150 Holleys. I knew lots of good mechanics in the late 1950's early 1960's that couldn't say Holley without a sarcastic cough!

The earlier book by Doug Roe (chief engineer on the Q-Jet) is also very good, but Cliff's book is written so that a consciencious 11 year old could rebuild a Q-Jet.

Jon.

Thanks for all the advice fellas. I think I will invest in that book; it sounds like it could have been useful to me several times in the past few years.

Cliff Ruggles and the above carbking Jon Hardgrove are the carb oracles known to me from the Performance Years Pontiac forum. Cliff is the Q-jet guy and Jon's speciality is the AFB but he has assembled a huge data base of information on many old rare carbs. http://www.thecarburetorshop.com/

the carbon floats on the old q-jet are porous and will absorb fuel over time and tend to sink a little with age, you can feel the difference in weight between a new one and an old one. I usually would replace the float with a brass one like they used to come with in the early 60's NAPA used to stock them.

Might want to try a leak down test to check the valves.