Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Quadrajet 7029282
Kavesh:
Many thanks for the replies. This gives me a little more confidence with my main body.
Very surprised about about the comment that there can be this liquid around the base. I assumed that area would be mostly dry.
Hopefully I get some time this weekend to sort it out and get it working nicely again.
Cliff Ruggles:
It would be difficult for fuel to get into that void in the baseplate unless the large rear bottom plugs are seeping out some fuel. I pressure test them here by putting 140psi of compressed air into the holes in the rear of the fuel bowl that supply fuel to the secondaries. With a little soap/water mix over the plugs you will very quickly find the smallest leaks. Although leaks are rare on the 1969 and newer units (despite what the "gurus" making Youtube videos tell us) you will occasionally find one that leaks slightly around the pressed in aluminum plugs.
The quick and easy repair is to gently "peen" the material over and around the plugs with a small machinist hammer. 99 percent of the time that is all that is needed to seal them back up. Dabbing any type of epoxy over leaking plugs, especially JB Weld is a complete waste of time. I see more carbs messed up by that stoopid repair that I can count. Building up a layer of epoxy over the plugs can hold the baseplate away from the main castings when it's tightened up. This puts the part in a bind, can cause the throttle shafts to stick, and also prevent the gasket from sealing causing a very difficult to find vacuum leak......FWIW.
Once again the "gurus" from ever Forum you go on, or Youtube video you watch on this topic tells us to put JB Weld over bottom plugs that most likely weren't leaking in the first place. JB Weld is also USELESS for that type of repair right to start with. It gets "soft" over time, and doesn't stick well enough to seal them up right to start with.......
Kavesh:
Thanks again Cliff for your advice. I will try and test the bowl this weekend for leaks.
I also thought it not normal to see so much fuel in the baseplate. I wonder if somehow there is a hairline crack in the bowl. Could that even happen?
I will post an update once I have assembled the carb.
Cliff Ruggles:
I've seen quite a few splits or cracks in the 1965 thru 1968 Q-jets that will cause them to leak.
The Carter castings are also bad for being porous and leaking fuel thru them. I've found quite a few "leakers" made after 1968 but almost all of them were Carter castings.
I've also found a few Q-jet bowls that were leaking between the passages under the DCR's over into the idle tube area. This is very difficult to troubleshoot and locate the problem but I've found quite a few of the Edelbrock 1904 thru 1910 units defective in that area and several 7041262 Pontiac castings doing the same thing.
I've also found a handful of later SMAB truck castings with the same issue. About the only way you can find that problem is to completely fill the bowl with fuel and eventually some will migrate over to the passages leading down to the mixture screws and start dribbling.
You can also fill the bowl mostly up with a soap/water mix and very carefully blow compressed air into the DCR's and you'll get some bubble over in the fuel bowl area where the idle tubes are located. That move is difficult because it's hard to seal off the compressed air during the test.
I have an Edelbrock 1904 in here right now that's got a bad casting. It was sent in by a customer who said it has never ran well despite numerous rebuilds and attempts to tune it. I found nothing wrong with it first time thru, then did a pressure test and found the driver side DCR passage leaking over into the main fuel bowl, so it's junk.......
Kavesh:
So I believe that the carb I was using was a Carter built unit, as it did not have the fill carb number, it was a 29282.
I decided to assemble another one from my shelf, with the correct QJ part number 7029282. I needed to fix the airhorn warpage which I did with some heat and G clamps. I had dismantled the airhorn air doors prior. After fixing the warpage I found that the shaft for the secondary doors was binding. I checked for straightness and it was fine. It seemed the 3 holes through which the shaft goes is now slightly out. After some though I used a perfect size thread bar as a file to realign the holes. I hope this does not create another issue!
Apart from the fuel inlet being damaged this body was decent. I used epoxy to seal the fuel inlet. I installed an inline fuel filter as I can no longer use the internal filter.
I am reusing the baseplate as I had previously repaired the shaft bushes.
While assembling the internals I remembered Cliff saying that the float clip will need some adjustment to work correctly. Armed with my needle nose pliers while holding the clip it vanished from sight never to be found again :-[ Anyways proceeded to assemble the carb for now just using the new needle and seat and accelerator pump and old gaskets. Once I confirm everything is good I will use my new gaskets.
I had previously tried to remove the ATP adjustment screw after removing the cap, but it would not budge. I hope there is no vacuum at that point.
I fired her up and see was purring like a kitten ;D. Mix screws are 2 and a half turns out. It was now late and performed some minor mixture adjustments. Curb idle screw is barely touching the stopper. I would have expected the motor not to idle but this was always my experience, choke fully disengaged.
Hope to take her for a drive later in the week.
Please see some pics will be posted below
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