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How to lean a QJet? and check for a bad choke?

Discussion in 'The Garage' started by sled_dog, Apr 10, 2003.

  1. sled_dog

    sled_dog 1 ton status

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    My K5 doesn't run as well as I really think it could or should with the brand new rebuilt 355. Lately it smells of gas after you shut it down and my friend said when he followed me to school today that he smelled gas strong while behind me. It also seems to build fuel in the exhaust cause when I let off the gas it shoots flames out and today I shut down and about 8 seconds afterwards it backfired. My gas cap seems to be bad because anytime I open it I get the good old hissing sound. My mom mentioned the gas smell and so did all my friends, I have a bad cold so I haven't noticed it that much. So how do I check if my choke is stuck open or how do I simply lean out the QJet? I have disconnected the choke previouslly and drove around and all it seemed to do was start slightly harder when cold.
     
  2. 75-K5

    75-K5 3/4 ton status

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    The two mixture screws on the front of the carb are how you lean it out. Screw them all the way in then back them out about 2 or 2.5 turns. It will run fine without the choke. Mine has survived 2 Indiana winters without it. It should start fine in the summer as long as you pump it properly. In the winter, I would increase the idle speed a little bit. You also may have to stay with it and keep nursing the gas pedal while it's warming up. I can't start mine and then go inside while it's warming up, I have to stay there with it or it will die after a couple seconds. Other than that, I don't really miss the choke. I have a hard time trusting chokes anyway, as all the other trucks I've had have had problems with the choke sticking. I'd rather know I don't have one at all than worry if it's working properly.
     
  3. blueturd

    blueturd Registered Member

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    The two screws that 75-k5 mentioned are the idle adjustment. This won't control the overall mixture. The first question I would ask is how did the carb work on the old motor? was it rich then, if so you need to make a jet or rod change. If not, your problem is probably choke related as you suspect... PM me if you have questions
     
  4. sled_dog

    sled_dog 1 ton status

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    well it seemed rich because I smelled fuel in the exhaust I thought but that was a 305. No carb adjustments were made just slapped the 305 carb on the 350. I know its the same carb doubt much different settings? I discovered that my fuel pump seemed to be coated in fuel when I left school so I think that may be a big culprit. Gonna change that out tonight.
     
  5. Goober

    Goober 1/2 ton status

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    [ QUOTE ]
    it shoots flames out

    [/ QUOTE ]


    I bet the chicks dig that!!

    /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif /forums/images/graemlins/shocked.gif


    Next time you pull into the driveway with the engine up to temp, pull the air cleaner and look at the choke plate. Is it sticking straight up and down or is it at an angle to the primary bores? If it's straight up and down (totally disengaged) then it's probably working right and you need to check other stuff.



    As was already mentioned, the mixture screws in the front of the baseplate ONLY adjust mixture at idle.

    Be careful when you try to lean out the idle mixure. If it's too lean at idle it will start to miss and send raw fuel vapor out the exhaust that makes it smell like it's too rich. Lot's of folks do that and when they can't seem to get rid of that "rich" smell and the miss, they toss the carb in the garbage thinking it's toasted. The best way to adjust your idle mixture is to use a vacuum gauge plugged into manifold vacuum (your brake booster hose will work great). With the engine idling, open the mixture screws up (unscrew, one at a time) and watch the vacuum go up. It should peak around 16-20 in/Hg but that number may vary depending on the condition of the engine, type of cam, phase of the moon /forums/images/graemlins/grin.gif etc. Just look for the highest reading. As you continue opening it up past the highest reading, the vacuum will start to drop a little and the engine may even stumble a bit. Turn it back to where you FIRST got the highest reading and then open (unscrew) an extra 1/4 turn. switch to the other mixture screw and do the same thing. Then, as long as you have everything hooked up, go back and adjust them one more time just to be sure. That should get you pretty close.

    If you don't have a vacuum gauge then you can come close by just opening the mixture screws (unscrewing, one at a time) until the engine starts to stumble a little bit and then turn them in (clockwise) 1/4 turn.



    If that doesn't do the trick then you may have to pull it apart and check to see how the float needle looks. That is the little pointy thing (technical term) that hangs off the end of your float. Its job is to stop the flow of fuel into the carb when the bowl is full. If your float level is set too high it might not sit all the way down in the seat, allowing fuel to keep flowing into the carb. You could also have some gunk (another technical term) sitting in the seat that won't allow it to close all the way. A classic example of that happens when you use Teflon tape to seal your fuel inlet threads and some pieces break off and flow into the carb.

    A long-shot might be a bad float. Your carb (if it is the stock one) most likely has a nitril float. It's basically a chunk of hard black foam that does not usually soak up fuel. I've never seen one that has soaked up fuel but I have seen them cracked in half. The older style brass floats were prone to spring a leak, fill up with fuel and just sit on the bottom of the bowl letting fuel just pour into the carb .......... that's bad.

    Anyways, a rebuild kit with all your gaskets and misc parts(about $15.00), a new float (about $8.00 IF you need it) and a few cans of carb cleaner will give you everything that you would need rip it apart and "freshen it up". If you've never done it before but you know how to use a screwdriver, you should be able to "quickie" rebuild on a Quadrajet. Just make sure you follow the instructions included with your rebuild kit (they have nice pictures to show you where everything is) and make sure you adjust the float level correctly. Float level adjustment is where I've seen most people mess up.



    <font color="orange">dyeager535</font> has a great Quadrajet reference page to look at.




    OK, here comes the disclaimer:

    I'm not a carb expert (but I did sleep at a Holiday Inn last night /forums/images/graemlins/rotfl.gif) but I have been messing with these things for awhile and I did learn a thing or two along the way.

    There are many other things that could cause these types of problems but I have found that FREE (checking adjustments) and CHEAP (quickie rebuild) fixes will take care of many Quadrajet problems on a stock engine.

    Once you get a wicked bump-stick and 11:1 compression you had better know what you are doing or your Quadrajet won't work worth a squat.


    /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif




    I KNOW that many folks here are great at fixing and adjusting Quadrajets, anyone else have some more ideas??
     
  6. sled_dog

    sled_dog 1 ton status

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    thanks I am just gonna put a new fuel pump on first, I don't think its supposed to be covered in fuel ya know?
     
  7. Goober

    Goober 1/2 ton status

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    [ QUOTE ]
    thanks I am just gonna put a new fuel pump on first, I don't think its supposed to be covered in fuel ya know?

    [/ QUOTE ]


    Can you tell where it's leaking from?

    If it's just a lose fitting it would be a shame to spend the money on a fuel pump when the old one in OK.


    /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
     
  8. mastercraftkpk

    mastercraftkpk 1/2 ton status

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    If yo are not confident that your carb is 100%, you should start there. Otherwise, yuo will chase this gremlin all over the place, never fully find it, and end up rebuilding the carb after wasting lots of time &amp; $$$.

    /forums/images/graemlins/usaflag.gif /forums/images/graemlins/k5.gif
     
  9. sled_dog

    sled_dog 1 ton status

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    I am going to get a Carb rebuild kit and a new fuel pump today. It seems to be leaking out of the top where the bowl thing like seams over the rest of the pump so the pump is definetally done. I described my symptoms to a friend with a 70s 2wd and he said thats how his acted before he replaced the fuel pump and now it runs great. So $20 I am just gonna do it.
     

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