VCCA Home Forums TECHNICAL - 1945 AND NEWER 1971-1979 Crappy Quad

Hey Guys; I am asking this for a good friend who has a '77 Z28 that he has owned since new. The car runs great as long as he starts it every day or at least every other day. If he lets it sit any longer than that the only way he will get that car started is pour a tiny bit of gas down the carb and away it goes. This supposed to be a rebuilt carb. Its got to be leaking down somewhere. Could someone give me a place to start to look. Thanks guys. Cheers!!

John

I have found this to be typical of the Quadrajet Carb.The fuel evaporates from the small bowl very quickly and often takes a bit of grinding over the starter to get running....after setting unused for a while or if engine was hot when shut off the night before.If the choke is closing properly and the fuel pump is strong it should start with out priming first.The bowl dose have plugs on the bottom which can leak but by the late '70's this was usually not a problem.If not external leak can be seen looking down into the throat with a light would find an internal leak.Also the fuel today evaporates so fast it may be adding to the problem.

I have three vehicles with Quadrajets and if they sit three or four days without starting then they are difficult to start. No priming is needed however.. The key is that while turning the engine over with the starter, the gas pedal must be constantly pumped until the vehicle starts. If the choke is working correctly (another famous problem with the Quadrajet) then it will only take a short time and the vehicle will start.

It doesn't really "solve" the problem; but I'm in agreement with Skippy..... just pump the heck out of the foot feed while you're turning the ignition key. Mine more-or-less fires right up; but I've pumped the accelerator 5-6-7 times in rapid succession while turning the key to start.

If the next question is 'flooding' - I don't think I've ever flooded it. It seems to need all the gas it gets from the multiple pumping on the accelerator.

Bill.

I agree the Q-jet is a pain to get going after it has set for some time. But a very quick starter if it sets less than a day, then if you do a lot of pumping it is prone to flooding, which don't seem to keep them from starting, But mine leaves a nice one foot diameter soot spot on the garage floor, I lay a piece of cardboard on the floor. I replaced one that was so corroded that the needle and seat threads were gone and the bottom plugs leaked all over the manifold, but it still ran like a scaulded cat on the highway. we were going to drive the 68 to G.J. but decided not to because of poor gas mileage (12mpg), running the A/C, but we will drive the Tahoe and pull the open trailer with the 53 onboard, since I get 14 or 15 mpg with the Tahoe. We probably will need the extra vehicle anyway, and A/C is nice in July.

Thanks alot for the tips guys; my buddy is going to let it sit now till Sunday then I'll take a look at it. He said a mechanic sealed the bottom plugs and it worked ok for the first couple of weeks but continued to get worse until it was back to normal.lol. Maybye he sealed it with something that was not fuel resistant. Anyhow I'll check it out Sun. Again guys, thanks for taking the time to answer the post. Greatly appreciated. Cheers!!!

John

I start each one of my cars as 42bill describes.....ya just gotta pump the heck out them! Even at that, I have never had one of my Quadrajets flood, except for a couple of times in the past 30 years when the float needle stuck open from some dirt.

JYd, have you ever had the soot on the floor problem? maybe my 68 is unique? I'm thinking I need to change the divorced choke operating mechanisum, I got a new one on ebay. ( I think a new set of dual exhausts may also help)

Yep, all the time! Not a lot but enough to notice, and the chokes work as they should. :( :( :(

I'm no pro with this problem but, like most of my input on this forum, I read something about it recently so I hunted the material down and found it in the "Collector Car Restoration Bible" by Matt Joseph.

Fuel percolation after motor shut down is one cause for fuel starvation at startup, when the heat from the motor causes the fuel in the bowl to evaporate by literally boiling it away. Pumping the gas while trying to start the motor will eventually get the fuel to the bowl, but it does take it's toll on the starter as it has to turn the motor several extra rotations.

Joseph suggests installing an electric "helper" fuel pump close to the gas tank wired to the power of the ignition. Then by just turning the ignition to "ON" for a few seconds before cranking over to "START", you'll get some fuel up the pipe to fill the bowl without having to use the motor to work the mechanical fuel pump.

The electric pump should be rated at a PSI equal to or lower than the spec for the mechanical pump, because some carb jets won't react well to over-pressure.

It might also help to keep the carb cool by installing a riser block to lift it off the manifold or, as I've read elsewhere, a stack of gaskets between the carb and manifold helps to insulate the carb and keep it cooler.

And of course, a set of dual exhausts couldn't hurt either . I'll have to try to convince my wife of that one next year. ("But we'll get WAY better gas mileage!")

In "Rochester Carburetors" by Doug Roe, he also mentions a problem with the casting plugs in the bottom of the throttle body. He attributes leakage from these plugs in the secondaries to running rich at idle, which might cause - I don't know - maybe soot on the driveway or something.

He notes that Delco and other companies sell foam pads that are supposed to stop secondary fuel well leakage, but these are only partially effective and can cause throttle body warpage if the foam is too hard. The fix he recommends is epoxy, and the photos show a substance that looks suspiciously like JB Weld.

Of course, if the problem is heat percolation and not running rich at idle, this fix won't solve the heat problem.

JB Weld is what the local Qjet guru uses. The new gasoline combined with water seems to eat away the potmetal in these carbs. The one I took off of the 68 was so bad the valve seat would not screw into the carb, no threads, the bottom plugs were eaten away. Almost every rebuilt Qjet you see will have the bottom plugs JB welded. The replacement I put on was a Holley rebuild. The new rebuilt carb runs much better, but the start up after a couple of weeks is still a bugger, and the soot on the garage floor is still there.

58BelAir-Your 1958 348 should have dual exhausts - thats the only way they came from the factory.....and it dosen't have a Quadrajet, would need to wait several more years for that feature......and gas milage 12 in the city and 16 on the highway would be considered normal.

It should either be a 4GC or a carter WCFB. You could not even fit a Q-jet on a 348 intake, no room for the secondaries
John

I know little about Q-Jets aside from what I've read. The book by Roe is all-encompassing for Rochester carbs, so it runs the gamut from monojet, 2G/2GC and 4 barrels from inception through at least mid-80's. I read (or mis-read) whatever I can get my hands on at this point.

My 58 has a 4GC, but single exhaust for now. We had a hack exhaust job replaced when we got the car road-ready in '03. It was probably replaced in the late '60's or early '70's and routed out the side in front of the rear tire on driver's side. Might be visible in the before picture on an earlier post.

I think I'm gettng about 13 MPG, but I haven't kept an egg under the acccelerator either. Not really my style to baby a motor with power to save some gas. For the money I'm putting into the motor this summer, period authenticity of the exhaust won't carry much weight if the one it has on it is working just fine.

Back to the electric auxiliary fuel pump; I just found the reader's letter in "Hemmings Classic Car" magazine, June 2006 #21 in the "Tech Talk" area. This also makes a third source, two general and one Rochester-specific, so the source-searching for info is looking prety solid now.

The reader's fuel starved carb was on a '49 Merc, so this problem is not unique to the Q-Jet. It also suggests switching over to a new carb of a different brand might not cure anything except a nagging incidental cash surplus. A good problem to have, but frustrated indiscriminate parts replacement almost always ensures it's temporary.

The technical advisor in Hemmings suggested a small electric pump "available at any auto parts store" which was not generally the case, as was pointed out in a follow-up letter in the July issue. The available off-the-shelf positive displacement rotary pumps have to keep running if the engine is running. Not necessarily desirable once the mechanical fuel pump kicks in.

The technical advisor went back and did his homework and recommended a 4.5 to 7 PSI pulse or bellows-type pump such as the Walbro WEP-38, which JC Whitney sells for $39.99 as item number ZX730906P at www.jcw.com . See this page: http://www.jcwhitney.com/autoparts/...6P&searchbtn.x=21&searchbtn.y=12

One letter writer had a 6-volt application while the other had converted to 12-volt. The JCW site shows this is a 6-volt pump but says "For all American cars and trucks with carburetor".

When it's all said and done, I would install this pump last if the vehicle is only idle for a day or two at a time instead of months. First I'd go with the passive fix of inserting about a 1/2" riser block between the carb and the manifold. Reducing the temp in the float bowl solves the problem of short-term fuel evaporation, pumping in fresh fuel at startup circumvents the symptom.

And of course, my technical expertise is not automotive, so this advice and five bucks is guaranteed to get you a pretty nice cup of Joe at the coffee place on the corner with the green sign.

Hey Guys; Back to this starting thing on this '77 Z28. When I checked this carb out after it had been sitting for four days fuel was pretty well gone in the bowl and it has already been epoxied. Put it back together and had my buddy start it. Pumped the livin' crap out of it and still no go. What I did notice is the choke plate was completely closed untill he started cranking it and it would open about 1/4 of the way. I pushed the butterfly closed with my finger and she fired right away. the auto choke was shot. Too much play in it and couldn't adjust it. I put an electric choke kit on it and it starts like it just come from the factory. Doesn't matter how long it sits. Case closed. I would like to thank you all for your replys. I personally am going to stick to my single barrels LOL. Thanks again all. I really appreciate the replies.

John

The choke plate will stay closed until the vacuum chock pull off works. There should have been a small sponge in the bottom of the baseplate between it and the bowl. It was "supposed" to handle any leakage that happened. Sometimes checking the fuel pump check valve will fix the problem. The fuel pump had a check valve made into the fuel pump to help this out. Another theory we had at the dealership was that the heat from the intake manifold would cause the gas to evaporate from the carb instead of it leaking down. I don't know which happened. I always liked them and if you built them with the right jets, 73's I think, they would run great and go through gas like pouring it out of a boot.