Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: turboguard on January 20, 2017, 01:01:30 PM
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So I just rebuilt my quadrajet using cliff's HP kit, and while it definitely improved my throttle response/performance (no more bogging from a takeoff) and gas mileage (this is the first time I've seen 200 miles between fill ups!!!), I've developed an idle fluctuation when warmed up:
https://www.youtube.com/watch?v=nQJdGQ06ES4&feature=youtu.be
There is a low thumping sound from the exhaust when the idle drops which I can only assume is a slight backfire?
Also, if I try a warm start after letting the car sit for a while, it will sometimes stumble and die if I don't give it a little gas first. Hasn't died in traffic yet, but it almost acts like it wants to. Picks right up with no stumble or bogging when I floor it from a stop.
I also installed a brand new TPS and MCS as well. The only other thing I changed were my spark plugs since they had fouled up pretty bad due to the carb running fairly rich before and also some oil leakage (replaced with NGK V-Power plugs)
What would be the most likely cause of this idle fluctuation? My carb didn't have it before I rebuilt it.
The other thing that is odd about my quadrajet is my airhorn doesn't have a rich stop screw (as in there isn't even a hole there where it should go). My carb number is 17085204, which according to my resources SHOULD have the rich stop screw, so I'm thinking the carb is kind of a mish-mash from the PO.
I still tried to set things the way they should be, but I don't have a dwell meter to exactly dial in my air bleed valve. It seems to idle the best at under 2 turns out from seated, which seems low? I have the idle screws turned out 5 turns each, but past 4-5 there doesn't seem to be any change in rpm/vacuum (vacuum is about 21 hg). If I fully seat both screws the engine stumbles and dies. Choke is fully open, and if I cover the primaries the engine does start to die as it should.
Another thing I just noticed was my Idle Stop Solenoid seems to be engaged all the time when the engine is on (I actually have it turned down so it doesn't interfere with normal driving)...don't know if that is a separate issue or related.
So basically, running like a champ except for this idle (which is embarrassing when stopped in traffic :-[). Any advice as to what I should start checking first? Maybe something to do with the fact it was running extremely rich before is why this problem just started?
Car info:
1985 Trans Am LG4
Stock except for AIR and Cat delete
Edelbrock 14"/3" open air element
MSD cap and rotor, Accell super coil and, plug wires
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Decided to make another video tonight...there is definitely a loud hissing coming directly from the carb, don't know if this is normal or not. Theres also a loud whistling when I open the throttle plates which I assume is caused by maybe an imperfect fit, don't know if it has any major effects or not.
Please let me know if anything in particular jumps out as a major issue to anyone, thanks!!
https://youtu.be/D-TqLcbpNHw
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Did you adjust the new TPS via the factory Service Manual?
Did you adjust the upper idle airbleed screw in the airhorn per the Service Manual?
Is the float set to factory specifications?
Might want to set the idle speed screw right against the linkage so see if it stabilizes idle speed instead of letting the computer control it.......Cliff
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I set the float as precisely as I could to 11/32 per the instructions
I haven't messed with the TPS adjustment (mainly due to not having the right tool to turn the little hex head), but when I tried to check the voltage by backprobing I was getting weird readings from my multimeter (the voltage would fluctuate slowly up and then down and sometimes show negative??), on both my old TPS and my new one...not sure if I was doing it wrong or my multimeter won't work right. I actually found a multimeter that apparently reads Dwell that I'm going to pick up today:
http://www.oreillyauto.com/site/c/detail/BOST/FIX7677/N1001.oap?ck=Search_multimeters+%26+analyzers_-1_1430&keyword=multimeters+%26+analyzers
Would this be sufficient to set pretty much everything to what it needs to be?
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Sounds pretty normal to me for an 85 T/A. The only thing I would do is get rid of those "novelty" NGK plugs and put a set of A/C Delcos in.
Double check your timing as well.
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Sounds pretty normal to me for an 85 T/A. The only thing I would do is get rid of those "novelty" NGK plugs and put a set of A/C Delcos in.
Double check your timing as well.
The V-Powers aren't really a "novelty" compared to other plugs out there, literally just a regular copper core plug with the V-tip which supposedly helps burn (couldn't hurt either way). Plug gap is at 0.35
My timing was 8 degrees advanced with the ECM disconnected.
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So I'm starting to think my idle problem has to do with the fact my airhorn has no rich stop screw. I've adjusted everything the best I can and it runs pretty good while in drive, but in park or neutral the idle is still very rough.
Would you be able to sell me the appropriate airhorn for my quadrajet? Or would it be possible for me to drill in a place for the rich stop screw myself?
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Can you provide a picture of what you are talking about (rich stop screw) and where it is missing on your carburetor?
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Can you provide a picture of what you are talking about (rich stop screw) and where it is missing on your carburetor?
Sure, I'll pop the airhorn off when I get home this evening and post up some pics of everything.
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Pics of the airhorn:
(https://lh3.googleusercontent.com/Af-NgDRPqtjorRVQY_jFh4z4o98FZzcSgOni80xv1irrsBaWPCw_nYikzc9dk-dr4jsSgw2YnPl9ETRVS9aiU1SGypTJx5M-spyzmH9ZFyUKCsT1ZBeuvJm0W7yzVlq4BNddyhrShKcUqFcmQVOdXbI7sznSLMkzkF2d-6EGRenQYVvoXnQewMXssuM3Qd4dCqKgbHVBtV9tAFrSiHW5Rgv1Acl4RRp2QsjaRFrl9D7rj0KiGfPxXYrnpRjxLAWFqeoIvRe3y_B8YwhayoB3Z2W7S2osauhHjpTlpIA0uC8eer4pyYBJMuKGIZFlrWsuGeHie6VEz65g_ENakOgB3RBjRN8K7EonXNxXrYXVCHqOIu8bH7reQy6EBHmcm09bM5zLMbHI4aF9wIzsGAt1yaVsaTwDSQqWdwAOVMnkiyqE3ZoMyCeqS-Q-T4LJXCQlvYH2J5BcGKVc6McozFY5XBVyA07Bg3uvgC15Fo_eA4myJlzyP6Etx3kBmbeqikDw5nrwK3IgvSJD1e8buJLl91FahNO53I6UQRir3x7i_l-6qxwB9mKrZximjz9KGJDJk-2AeWZffvaycmG7KXmy7E8exfxv-3vLCYyKDACPabEBAYwbX5TP=w2328-h1310-no)
(https://lh3.googleusercontent.com/5558aqlMM4rk_HuBEKLOB8rk2mvWxTf-wIbYRwAWdC5YolYadRS9Pyfz-amjauc3heHVikFDycBUp7XoUJepYWc025_5wUGWH6WP--gC4F1wb36wgVUxXq2B3Bj0bZcSUlCWFNZ_CnyJ0VZxQJ-tahyRCPJuLdIPS2wKW3Dr8S88mfmeK89EEzx0oRqjTtbx0P_ezuWEz9qg0jFWwu7CCLa5It57B3y9Ium0OYghqH9JCJJBMtl8Pm3-BMbOSyF6ld-J4ZGlr4MEEIMh0L3UDrz80pDzdEpT5Mw2uqyG93O21_DX4VHad-V_uAGk7P-ab40os7Ix6qYlhmk7D15J5Y7bPzV6hjB1HKE8gu4k4eO7QqCO2gB0hDcPOqiWz97c8AeOJnxWzVpB2oxI_TcAtcKhQlwXpWpOjN2PBncgGge4kpaYaElbj0BdUtqL10Ig14NQF4EHRbsBA-XT4d3hh9xfNLBJ1ZCplF0_hmOQP2pS9d1UaTL5wscZH0eDf9RjHW2v81tFR49OWSkfCyd1D5qy36w9lbfT_iwrb5DNIgYNoJHtub_TY0ZmUKQB_ZRPZID4-tzB3peCB0Umz17fWpHH0fJBR39UBix-Fkq1HBrCb_ij=w2328-h1310-no)
Close-up of where the rich stop screw should be if this were the correct airhorn:
(https://lh3.googleusercontent.com/WZb_fDlUU3xiQtLXFf8u6SXqHxlPYza4aQdcqpfaGruCpQnKoDjyD5Hdli2cfrnZ49F6hETucSFMYFOMcM9Xsymc5C3KNDf5Smp7uE5SOobbi8xd3ZLt_S3wufU3yTDC14xdTEvuJiss9KvV8sK8dGhlbGEhxG-p3KudfX9lCwpqovsrxwXgGfPBDCTZxf51BaTKDJ1yOGwvKgTNujdyUzRRx80r8CltLg-0TDTbmasDHXqURofCBsPU6CQaTY7stWkDvuPqvfp8FAMMy4nZKkME7LIlVUKrIGxLXhrYNUDmnhwL1009fnxoCi_xk5ksnzByBCeYg-U-tt_E6QaGkmib4fXla7N_ppTXLS0SK8qTlUNELQvLjzUuzUysA-nnBdQWDxRv0XBAteMegx1-xe6zm-sr4L6A_26PZGykO6hybDH68JVP8PxMj12UZid91NC4hDMrDD-TN3ijWV5gIh19KAZ62x7wPIWtK6usEr7X-9mGSFK66OXJ7y9bTMqqGDaEl8PdnGgvLeeL6gH9FwPQqQ9nCWPTMNsSycPbZLUcNA8BjMVNEg2QqnGP_HpYVJhIiw5cSTGL5O3M3jLSeG2JyYImGLib5XawXbCUigzPqqpK=w2328-h1310-no)
The carb number:
(https://lh3.googleusercontent.com/U0br4ANkXZywX74WnY2BIFfOlEdSDzFnekBrw_j_EvIvrMr93uXcAKaE0VfWHuz0a3LPPd28Yglq-W3bR5Pk2edsZZIi0KXNqXc4FMJW7GtN4Khh-zGplcsOKgSPYQYcdUo3kW7rB19MB8gVWar6hnHaw4T9ZYV47Df8-sQZETa2cWAHjEZPj-zvKmiYMu2zkk-kB6goJYaKxq_zBxNpJOdHNay08jxyG12S-aBc6AcOw3DPgxGpml0I-qUo1Q6HmLHVhTT1LcBTAgL47BGRE1KWWZNP-aFhKBVzHJ1kzvfTFjm39aWbG3fGnC5gBonb5T3dLbmaTTh4gEOFcaabvz3WtchhouZjpTbb5Q1HgGEk3e8BnYPL7IR7DcadF2GMANdfMybng_eey7W7PHaCvEf5Isy5naZufUtyVwiwwSYeLdLWMrst8SOQnmDdciqcF9eEdsZX-9IVLUaLImuLYIhTBjXHHXdTHNWeg4TsLJT2nlfQw1LE3ZfvR7RuDsSqE-KfOesBtn5fZrJkjdeMwKED8jWP9iLKtDUeSrlyvkCmkGVJCRP3IztLKZfgvEXw26pyA0xskR3J2cW-yZYDeoVcBCH6bZLFS6x_YPsyav0C2z32=w2328-h1310-no)
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Another pic of the carb w/o airhorn:
(https://lh3.googleusercontent.com/mzAyh0d-wwUbP490kETEE1j4E4W8HTg-260TTWzGXkIvVywb7BL0kKQF35x0401NjOQtjVfUSUEzwMaJze4CssOvp-aoIQsKozm9ZBnvG255YNuJhEI1m4K4YhhcqpFFHIJHuX3Z41HMpP-ZU9i96zJo8Q-q_yjZsQObCB2FWenDT2aS5dy7Esx7T-Cq-AafhqaubbtQGDwb7vk83hu71qe4NAtmaDe_CYPCbaPF8n098TVNTNuKi_huJId_0A7RIbBZdLl57XQrP4FTxfgYDgawEjd8SQjl83Sic_lRXoUZI2Lm_G62MACZSCy-_S7cZWjd6pv7DrqeFUsEYUPofg8nggXzb31AuWpN0g-5PuGNVYqr2NJZPniygl4arVh25TT_DeQ5xPL8Wc7U5ftO_ZUjanwbJb5_RH0VLtmYrgrX1J-_DdnokqCVK2UyLzJPTL2bWdVMK0SvdbBmp9Pw26-rjs0qJeK18Pyj83PuOnERMr6-0IjZhg6qz_Gu1lv5hFIKaqdqv1vp7LOQAO5MMl3Dan_l4rSPQVnZuJpeDvm048K6K8fig57f320YHwZrfGG-pzmfp_BnSM2yK5YZbdt1Pf0n8VgEF2AsikWifZ7exFva=w2328-h1310-no)
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I'm not seeing the pics?
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I'm not seeing the pics?
Sorry, Google Chrome tricked me into thinking the links would actually work for other people :P
Here is a direct link to my album, should work for anyone:
https://goo.gl/photos/jDKXybfKPorA85Hx6
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That worked.
That airhorn doesn't have the adjustment most have to adjust or limit the height of the primary metering rods. It would have nothing to do with idle quality in any way.
I also see that the upper idle airbleed adjustment parts are missing, the one with the two "O" rings on it. That needs to be in place to fine tune the idle system once the carb is placed back in service.....Cliff
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That worked.
That airhorn doesn't have the adjustment most have to adjust or limit the height of the primary metering rods. It would have nothing to do with idle quality in any way.
I also see that the upper idle airbleed adjustment parts are missing, the one with the two "O" rings on it. That needs to be in place to fine tune the idle system once the carb is placed back in service.....Cliff
It has the IAB valve, just had it out for the pics.
I know you say the rich stop screw doesn't affect the idle, but with it not being there, wouldn't that also effect the IAB valve's travel since it would cause the little piston to move further up, pushing the IAB valve more than it should?
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They made those carburetors with and without the limit or rich stop. If it's up against the IAB's valve and pushing it to the deepest position you still should be able to use the adjustment it the airhorn keep the idle from being unstable.
Do you have full control with the idle bleed adjustment in the airhorn?.....Cliff
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They made those carburetors with and without the limit or rich stop. If it's up against the IAB's valve and pushing it to the deepest position you still should be able to use the adjustment it the airhorn keep the idle from being unstable.
Do you have full control with the idle bleed adjustment in the airhorn?.....Cliff
So after I drove home (~30 min) today I hopped out and immediately hooked up my dwell meter...with the IAB valve screwed all the way in to about 1 turn out, it idles the highest and smoothest (but still stumbles and backfires slightly), but the dwell is pegged at 54°. Once I start backing it out, the idle drops slightly and starts stumbling and the dwell goes down into the 40's and slowly decreases as I unscrew it. I can unscrew it to the point where I hear the piston stop hitting the IAB valve's rod and actually tick on the airhorn itself and the dwell is in the 30's. I have the idle mixture screws at about 3 1/2 turns out during this, and the lean stop screw set approx. 1.304 inches according to the guide.
I'm kind of at a loss as to how to get it running perfectly without scrapping the whole thing honestly, lol.
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3.5 turns out from seated is pretty lean with one of those carbs as the mixture screws have metric threads. Most end up 5-6 turns out from seated to get enough fuel to them to idle well.
I would install the correct airhorn if doing it here as I like having the limit for the metering rods so we can fine tune them to run well if the M/C solenoid quits working. We probably have a dozen of them in the core pile.....Cliff
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3.5 turns out from seated is pretty lean with one of those carbs as the mixture screws have metric threads. Most end up 5-6 turns out from seated to get enough fuel to them to idle well.
I would install the correct airhorn if doing it here as I like having the limit for the metering rods so we can fine tune them to run well if the M/C solenoid quits working. We probably have a dozen of them in the core pile.....Cliff
How much would you charge for a good airhorn? I think my best bet is getting the appropriate airhorn so I can better tweak the settings, plus my airhorn is slightly warped anyway so that's probably causing some issues too (although I am using the thicker gasket you sent which is probably helping a lot).
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We sell those for $15 plus shipping. We're here 8am-4pm, M-F EST...tks....Cliff
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Thanks for the awesome airhorn! it even had all the plugs and rivets still in! Gonna clean it up real good and install it tomorrow and see how much better my car will run with the proper adjustments! ;D
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You are most welcome. I ended up taking one from a complete core as I wasn't happy with the ones in the core pile. We've been robbing parts from them for many years so couldn't find one with everything on it and unmolested......Cliff
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So...this will be my third teardown and rebuild of it, and after getting the correct airhorn on, it runs even better than before. Takes off like a bat out of hell and screams at full throttle! But of course...still running into idle problems (of a different sort this time).
This time I actually removed my old idle pickup tubes and carefully installed the new ones I received with my HP kit, making sure all passages were free and clear. My primary throttle shafts were already bushed, so along with bushing my secondaries, both shafts are freely rotating. There is a very slight amount of left-right play on the primaries when they are open, but they close snuggly and I tried my best to center them in front of a light. The only other thing I did regarding the throttle shafts was the fast idle cam piece (the one that is spring loaded onto the adjustment screw) was having some clearance issues with the throttle plates closed, causing it to stick, so I filed a bit of metal off of the piece so it would move more freely and let the throttle plates close fully without any hangups.
I actually got a hold of the Quadrajet Thexton tools and meticulously set everything to the proper stock settings using the tools (float, lean and rich stops, IAB, TPS). I set the idle mixtures screws to 3-3/8 turns out as per the instructions that came with the kit, tools, and my service manual. After warming up, I connected my dwell meter and found at stock settings the dwell was in the single digits, so per my manual I turned the IAB valve in until the dwell was fluctuating around 30 degrees, which did take several turns to get to, but never bottomed out. (Remember before with my old airhorn this was impossible, dwell was pegged at 54 no matter what!). Idle stop solenoid is set fairly low and engaging properly only when it should, so its not holding the throttle up. PCV is hooked up and functioning correctly. All vac ports hosed or properly capped. Still using the thicker airhorn gasket.
Now the main problem with the idle is that it is too high! Fully warmed up, choke properly open and fast idle disengaged, I get 1000-1100 in park and about 750 in drive. The throttle plates are fully closing, and the linkage is all the way against the idle adjustment screw (which is just barely sticking out of the hole as it is, where as before I actually had to turn it in to get the idle high enough to be smooth).
Some other symptoms: The dwell varied about 10 degrees with my air cleaner on and off ( I have the 14" edelbrock open air element with a wix filter). When I rev the motor in park, the rpms seems to be slow to drop back down to idle (the rpms drop to about 1500 and then slowly go back down from there, where as before it was almost an instant drop after releasing the pedal). Still getting what seems to be a slight backfire and idle and low part throttle. Sometimes get dieseling after shut off, which is expected I guess when the idle is too high?
Any suggestions on what's going on this time? Too rich? Too lean? I know a vacuum leak could be suspect, so I'm actually gonna go buy a propane bottle today and see what I find around the carb and intake manifold. Aside from that, any clues what I need to be looking for?
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Forgot to mention my timing is set at 8 degrees with ECM disconnected, I haven't messed with it yet because I had a hard time even getting to the nut to loosen the distributor, lol.
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Can't say as I've ever had to remove any material from the part on the throttle shaft that contacts the fast idle cam if the correct parts were being used. Having to do that raises a "flag" here.....Cliff
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Can't say as I've ever had to remove any material from the part on the throttle shaft that contacts the fast idle cam if the correct parts were being used. Having to do that raises a "flag" here.....Cliff
It was the little free floating piece where the bottom touches the adjustment screw and the top rests against the fast idle steps...near the center of if there are two little spots on each side of the hole that stick out against the outer piece that holds the adjustment screw. Clearance was fine if the throttle shaft was held open slightly, but when rotated to fully seated the little metal tabs would get held up and cause the shaft to stick, so I just shaved the tabs down a little to where they wouldn't stick when the shaft was fully rotated closed.
I'm starting to think I may have a major intake manifold leak...I'll find out tonight when I probe with some propane!
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Provided that the throttle plates are well seated in their bores at idle speed with the adjustment screw backed off and you are still seeing high idle speed, there has to be air getting to the intake from another source.
This assumes that you don't have HUGE idle bypass air holes or holes drilled in any of the throttle plates......Cliff