Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: stushug on June 01, 2017, 10:23:43 AM
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I have a 1977 Grand Prix. I just had the engine rebuilt (stock specs). The carb was leaking from a lot of different places so I had it rebuilt also. Now, if I go past 1/4 of the way with the gas pedal, the engine coughs and sputters, while barely accelerating. I checked ignition, compression, wires and plugs and everything is fine. As long as I don't go past about 1/4 throttle, the car accelerates fine. It also idles perfectly. Looking for some help on this, any suggestions would be greatly appreciated.
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Looks like it's running out of fuel. I once had the same problem when I forgot to install the spring under the apt screw and the primary rods were going own all the way, almost blocking the jets.
What is your carb number and with what kind of parts was it rebuilt ?
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Frank,
Top row of numbers: 17057274 Second row: 1517 ARN. The carb was rebuilt by Dennis Barker, so I assume the quality of parts were good. I'm thinking it may be getting too much fuel, I can always smell it, and the mileage is down to about 6mpg. The car used to get about 10-12 city and about 15-17 highway. I pulled a plug today and it's pretty loaded with carbon. I'm attaching a picture. Thanks for the help!
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Very good unit, and that is most likely the original from your car, 1517 is the date code, 151st day of 77. Did you ask Mr. Barker about your issues ?
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Yes, I've spoken with him over the phone, but it's very difficult to work that way. He's located in Colorado and I live in Pittsburgh, PA.
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A simple test would be to pull the power piston up (thru the vent) and see if the same thing happens. I'm pretty sure I read somewhere about how to fabricate such a hook/tool. Maybe it's in the Doug Roe book or a Delco Rochester service manual. Not that complicated.
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I don't understand how to do that.
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Piece of wire bend a hook on it & go down through the bowl vent.
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I assume I do this while the engine is running and work the throttle after lifting the piston?
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Today I went to try what you suggested Frank, and I think I found the problem. When I looked into the vent, I saw that the gasket between the carb body and the top has that hole completely closed off. Just to make sure, you meant the round vent just in front of the primaries that sticks up into the air cleaner, correct. Should that hole be blocked off? Maybe Mr. Barker made a mistake and placed the incorrect gasket?
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Unlikely the gasket has anything to do with it.
That is an excellent unit, same exact part number I've been using for decades and it's successfully powered 4 different engines in my Ventura from 300hp to over 550hp.
If it were assembled correctly with good parts it would be flawless. That carburetor doesn't even need any help anyplace for what you are doing, they are as delivered one of the very best q-jets every made. Time to look a little deeper, I'm sure it's something very easy to correct.
I would also never "assume" a rebuild has good parts in it. I have many parts that we use custom made for us because the ones from the suppliers don't make the grade.
This includes the "blue" accl pump seals, they are complete JUNK, and swell up and fail quickly in this new fuel.......Cliff
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Before the rebuild, the car ran fine until one day the carb started leaking profusely. There was fuel all over the intake manifold. I had dropped the car off for a front end alignment and they called to tell me they couldn't get the car started. I had it towed back home and sent the carb for repair. When it came back is when I noticed the acceleration issue.
Cliff, when you say look deeper, what would be the next step? Do you think I need to purchase one of your rebuild kits to make sure I have better parts? I would have no problem there. The car is barely driveable as it is running now.
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That would be the first place to start, install good parts and verify correct float height, sealing at the gasket under the fuel inlet seat, make sure the power piston hanger arms are exactly level and even, pressure test the bottom plugs, check throttle plates for full closing/alignment, and look for obvious mistakes or problems like a leaking accl pump check ball, sticking power piston, not sealing the gasket well between the main body and airhorn (warped) etc, etc......Cliff
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Which kit do you recommend? My carb is a 17057274
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I would use the SR kit, it has everything to do a complete/correct rebuild on that carburetor and get it up to par for this new fuel......Cliff
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I purchased the SR kit, and redid the carb today. I got a little bit of improvement, but the car still won't run right. Now, if I go pedal to the floor, it still coughs and sputters until I back off the throttle to about 3/4 to the floor. The things I found wrong when I opened the carb were that the old float was partially disintegrated and the spring for the secondary plates was too tight. I'm not sure what to check next.
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Is that the only place you are having issues, going to full throttle?
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Yes. If traveling at lower speeds and I go wide open, the car starts to sputter, it has even stalled out a few times. As the rpms rise, it behaves a little better, but it never fully recovers. When it's acting like that, if I back off the throttle just a bit, the problem mostly disappears. As long as it's at full throttle though, the problem persists. Thanks for the help so far, Cliff!
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Did you install the new secondary plastic cam and spring from the kit?
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Yes I did.
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I'd try making adjustments to the spring tension and see if it improves.
Also make sure the choke pull-off is holding the secondary flaps tightly shut at idle and no slop in the linkage. The pull-off should open in about 1.5 to 2 seconds from compressed to fully open. Also make sure that it is holding vacuum.....Cliff
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I checked the pull-off and the linkage is fine, it holds the flaps fully closed with no slop. It is holding vacuum, but I did see that when I applied throttle, it went from compressed to fully open almost instantly.
As far as the tension spring, I'm not sure where a good starting point would be so I'm not sure if I have it too loose or too tight. If I started at no tension, is there a number of turns or partial turns as a general start? Or maybe using clock numbers such as one or three o'clock from zero tension?
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but I did see that when I applied throttle, it went from compressed to fully open almost instantly.
It should open much slower, about 2-3 seconds from closed to fully open once you go to full throttle......Cliff
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Does that mean mine is bad, or is there a way to adjust it? If it needs replaced, I assume you sell them?
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but I did see that when I applied throttle, it went from compressed to fully open almost instantly.
It should open much slower, about 2-3 seconds from closed to fully open once you go to full throttle......Cliff
Does that mean I need to replace it, and do you have replacements? Thanks.
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Cliff has them. Bet it's been modified.
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Yes, we stock the good ones with a straight inlet so they are easy to modify....
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I purchased one of your pulloffs, installed it today and didn't notice any difference. With the car at full throttle, it keeps stuttering and backfiring. If I back off the throttle just a touch, the car accelerates much better.
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Do you have a restriction someplace in the exhaust system?
Your problem sounds fundamental and may not be related to the carburetor provided you have done a complete/correct rebuild with good parts and correct settings......Cliff
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Cliff,
The carb was just rebuilt by me after purchasing one of your SR kits about three weeks ago, then I changed the pulloff on Sunday, on your recommendation. The engine is a rebuild with about 3K miles on it, and the dual exhaust, from manifolds to tailpipe was installed right after the rebuild. There are definitely no restrictions there. I will go over everything again, but I have checked fuel pressure, vacuum lines, exhaust and engine timing multiple times. I'm running out of ideas. I appreciate your suggestions and will follow up. Thanks.
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fwiw i think its ether a tight intake valve or the distributer . i don't think its in the carb it may even have a lobe on the cam going flat .
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I use the exact same carburetor on my 455 up near 600hp. It was also used on 3 previous engines that were in my car and has been flawless the entire time.
https://www.youtube.com/watch?v=6zVdoLR-VzM
I have done a LOT of testing and on several occasions the engine "puked" on full throttle starts with the following set-ups.
Installing a K & N X-Treem lid
Installing an RPM intake and shorter air cleaner
Putting a full open spacer on my factory dual plane intake
Installing a Performer intake on my current engine
The Performer intake has very restrictive runners to feed nearly 600hp so the engine hated it.
My carburetor is not "modified" in any was far as grinding or "porting" it anyplace, it is basically a stone stock part recalibrated for exactly what I am doing.
It uses the exact same parts we sent you for your carb except for jets and metering rods.
Hanger is an "L", and we change metering rods based on weather conditions at the track. The metering rods are all custom machined from the same cores for very precise metering changes.
I suspect a fundamental issue someplace not related to the carburetor. This assumes that it is completely/correctly rebuilt with correct settings and nothing plugged up anyplace internally.
If you can't find a suitable replacement we test carburetors here for $35 plus the fuel (usually about $15)......Cliff