Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: Ponchonutty on September 04, 2025, 05:35:35 AM
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Thanks for letting me in Cliff. So here's a long winded tale of my issues. Bought a 79 Trans Am with matching Pontiac 301 and Th350 that was gone through mechanically. Sent carb off to Classic Carb Rebuilders in Eden NC. I knew the carb wasn't right from the start due to the Holley reman sticker on the side. Also, the throttle would always hang up just off idle so fine tuning it was impossible. CCR said the carb was warped and since it's not the original carb I should look for a better core. Found one that was listed as a Pontiac one but was for an Oldsmobile. He then called me asking if I needed all the extra brackets on the old carb. I said yes, I need those because one bumps up idle when the AC is on and the other shuts off the AC compressor when floored. He said he never seen such a thing (first red light). He also said the old carb was full of rust in the bottom of the bowl. So, I replaced every single fuel related item including the tank.
Got the carb back and it still would hang up at idle. It would bump up about 400 rpms. when it would do it. So I messaged CCR again. He stated that possibly the shaft he used from the original carb may be slightly bent and for me to send it back. I do then when he gets it he calls screaming I am name bashing on FB. I assure everyone I did not. I merely mentioned I still had an issue that I have to send the carb back to him on another's post. After him yelling at me he said he was going to blueprint this carb and make sure everything was in tolerance. Grand total of about $800 I still have what I believe is carb problems.
For the life of me I can not get the mixture to richen up at all. It starts great. Off, part, and 3/4 throttle is fine. Floor it and it slows down. Sometimes will even backfire. I do have a wideband and its showing it's way lean like in the 20's cruising and pegs at 50 when WOT. Only time the wide band shows decent numbers is when the choke is on. The secondary does indeed open. I can see fuel pumping through it.
Before anyone mentions a plugged exhaust, I just replaced the original exhaust with a Pypes kit. Also swapped the trans to a 2004r but had this issue with the original one.
Carbs are outside my comfort zone. Had I known about this site I would have given it my best and tried to rebuild it myself. Right now the car is at a buddy's shop. He suggested getting another carb to see if it changes anything for the better. Found one that's in great shape to see if that corrects anything. Cliff, if I drive to you, would you wanna rebuild another?
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Here’s a video.
https://youtube.com/shorts/zVpcvFY8sj8?si=6tn45XKpGjVJ1K5w
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UPDATE: So did a carb swap, that changed nothing. Car definitely is running lean. Squirting starting fluid down the carb while running causes the engine to smooth out and the o2 readings to go 14-12. Smoked the intake and nothing. It's sealed up tight with no leaks. Next is to check fuel psi when driving. Did check it out at while cranking it and it showed 7psi. Not sure if maybe I am losing volume when flooring it or not. This test should tell me. If it checks out then I'm lost. If timing is that far off it should crank real slow when starting but it doesn't. Will update when I find out about the fuel psi.
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UPDATE: My buddy who has had my car for a little while now finally was able to dedicate a few solid hours to mess around. Said that he happened to notice the secondary lever not coming up with the throttle opened up. Took the top off and inspected noticing no plastic cam. I'm hoping this is the issue all along. The other carbs he tried were literally straight off junkyard motors and not cleaned up. Still unsure if the wide band is even reading correctly.
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If the cam is gone it won't raise the rods, so it will be lean. Should just about die.
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Little update. So found out not only is the secondary cam non-existent, I've got a plugged POE. When I sent this carb in the first time, I was told it had rust in the bottom of the bowl. I took a mason jar and cranked it over a little and sure enough, rust (pictured). That prompted me to replace EVERYTHING. Tank, sender, all lines including return and vent, and pump. Still had the sticking problem so I sent it back. He sent me pics saying the carb still has junk inside as shown in pic of cut open fuel filter. I don't know how that could have happened since again, ALL OF THE FUEL RELATED ITEMS WERE NEW AND EVEN FLUSHED PRIOR TO INSTALLING THE CARB THE FIRST TIME. Anyways here I am rebuilding this carb for the 3rd time :-[
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Second rebuild. No warranty due to contamination according to the rebuilder
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Plugged POE
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Filter as shown last year allegedly from fuel contamination on an entirely new fuel system.
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What I found in the first rebuild which prompted me to replace everything.
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This is a horrible picture I took from a video he sent me with him running it on his test engine. This was WOT and this is the widest the secondaries go. I was told he pulled a lot of performance out of the carb due to being for a Pontiac 301?
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He got you good, wow. That puller pic is the air bleed the larger tube is the pullover.
I don't know about 301's but the sec. should open farther than that.
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He got you good, wow. That puller pic is the air bleed the larger tube is the pullover.
I don't know about 301's but the sec. should open farther than that.
Yeah, After I bought Cliff's book and went back through the archives of my messages with him, I realize what I was failing to see now.
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This is a horrible picture I took from a video he sent me with him running it on his test engine. This was WOT and this is the widest the secondaries go. I was told he pulled a lot of performance out of the carb due to being for a Pontiac 301?
The air valves will NOT open fully unless you put load on engine driving the car.
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Somehow he can do it with other carbs like this one he did after mine
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Video of his test of my carb https://youtu.be/Eeq3wzPrvoc?si=HCe6-SVF82VlPvO1
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That about normal for just winging the throttle. I thought he had it on a dyno.
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I don’t think the engine is under any sort of load. Here’s another carb about a day later. It too was for a Pontiac https://youtube.com/shorts/Ugl6HN0t3A8?si=HOU7m8e1-4aUKyKO
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Plugged POE
That carb does not have the POE, (pull over enrichment), what you have circled in your picture is the secondary air bleed tube.
If it had the POE system, there would be a 3rd set of tubes located in the slightly larger holes just ahead of the air bleed tubes, and these would be longer and thicker. In addition, the discharge holes for the POE are located just above or below the choke blade when it's closed.
If those are not there, the carb never had a POE system. If there are discharge ports, then it's possible that someone pulled the tubes at some point and didn't replace them.
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Sorry. New to the quadrajet terminology. From reading about a plugged secondary air bleed tube it said this condition would result in rich idle conditions. This can't be true since my carb runs extremely lean.
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Secondary air bleed tube would have no effect on idle, but it would definitely affect WOT secondary metering.
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So this is a late 80’s Chevy style carb body with the top of mine after installing the missing secondary cam. Once the o2 sensor warms up, you can see she’s now twice as rich as it once was. So, rebuild number 3 on the way. DO NOT SEND A CARB TO EDEN, NC!
https://youtu.be/KID_MnNmRJ8?feature=shared
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Well my stopped by my buddy's shop to see what all he's found so far. He said he was appalled at how dirty the inside was. You can see the old gasket that was reused. He said chunks of carbon fell off it when removed. Also the jets all look used. He said although there's nothing technically wrong with reusing parts, a "professional" would never do that. Everything is nice and super clean now with no old residue left. He said "no wonder why Classic Carb Rebuilder said if this is opened, warranty is voided." I told him I already sent it back once and he denied warranty saying my fuel was contaminated. He then asked how many tanks of fuel I ran through and I said at least 2. He said every fuel sample he's taken is fine.
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Other side of gasket
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Looks good and clean now. Buddy also said it looked like subpar parts were used too
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With a sufficiently weak preload on the spring to the air valves you can make them open whenever you want.
The same settings in a car the car willl nose dive at WOT.
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The only advice I can give here is to avoid commercially "remanufactured" carburetors. I woln't touch on here and recommend others to the same.
BTW, Holley is one of the WORST companies to ever touch a Q-jet. Every single one from them I've seen has been a complete pile of bovine excrement......FWIW....
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The only advice I can give here is to avoid commercially "remanufactured" carburetors. I woln't touch on here and recommend others to the same.
BTW, Holley is one of the WORST companies to ever touch a Q-jet. Every single one from them I've seen has been a complete pile of bovine excrement......FWIW....
Yes I've known this for decades and wasn't surprised when Tim said what I sent was junk. I sent him a virgin carb to rebuild twice still having the same issue plus now running super lean with reused parts and junk new parts. over $700 deep when all of it is added up.:(
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Not good news. I'm not familiar with your "builder" but if you've invested that kind of money with him you'd think he'd do what is needed to make sure you have a good end result......
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Yeah, I know I stand by my work. Heck I have to travel and hour to do a reset of a remote starter that I installed over 3 years ago. It was something the owner did to the car. Guess what, I won't charge her for it.
Tim, tongue lashed me when I sent it to him the second time. He accused me of me bashing his work online saying I was hurting his online reputation. All I had said on someone else's post that I was sending it back to have him take another look. I asked for him to provide proof I sullied his name of which he could not. He had me by the balls and charged me another $200 to correct the original reason for having it rebuilt. I spoke to him several times after I noticed still having issues and he "assured" me it wasn't the carb and that it has to be something with the car.
I bought another correct junk carb core and will be dropping it and the frankenstein carb to Ray Klemm. I suspect the throttle body is either junk or needs shaft bushings. When I last ran it in the garage, it was where it needed to be via what my wide band showed. Let it sit after running for a bit and restarted it. It then began to lean out more as it ran. When I pulled it off, there was what looked like moisture on one side of the primary and secondaries blades and gasket. Thought that was odd but it was super humid that day. I noticed later if I tap the rod that holds the secondary baffle plate, it rattles on one side. That shaft appears to be new. Either it is wrong or there's wear in the throttle body. I do know Tim said my original carb was junk because it was warped. He did reuse that part of the old carb due to the brakets needed for the solenoids for the AC system.