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how do you tune a carb?

This is a discussion on how do you tune a carb? within the Classic Muscle forums, part of the Vehicle Specific category; Originally Posted by bamaz28 meaning i never use them, not that i dont know how. OH my bad I take ...

  1. #21
    Rockin the Ruckus! 02Sweet's Avatar
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    2002 z28 camaro

    Quote Originally Posted by bamaz28 View Post
    meaning i never use them, not that i dont know how.
    OH my bad I take it you use the "street tune" method

  2. #22
    Alabama Member bamaz28's Avatar
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    06 Jeep Grand Cherokee.
    02 superchipsZ28 M6(sold)

    Quote Originally Posted by 02sweet View Post
    oh my bad i take it you use the "street tune" method
    say what you want but we cranked out over 50-75 sbc no problems

  3. #23
    Rodzilla Tha Cavity Filla zero_proto's Avatar
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    99 Z28 with an SS complex

    Quote Originally Posted by cycowrencher View Post
    You will need a timing light to tune that car correctly. You will also want to buy a vacuum gauge. You can buy a cheap dial back at your local parts place. Warm up the engine, drive around the block, or run an errand, just make sure the car is at operating temp. Disconnect and plug the vacuum advance to the distributor.

    The only cam grind i can find from Isky is a 264. This is a .450 lift cam and should have 14-17 inches of vacuum in a 9.0:1 350 cid motor. If that is what is in your 307, you may have a hard time getting 12 inches of vac.

    Set the initial timing at 12-14* before top dead center. Your idle speed should increase, unless your timing is too far advanced. Then turn down the idle screw until the car idles at 800 rpm. Turn the dial on your timing light to 35* and rev the engine to 3000 rpm, you should be able to see the 0* mark on the crank pulley. Adjust the dial until the 0* mark on the pulley is zeroed to the timing pointer. Read the dial, this is your total advance, this should be between 35-39*. Once this is set up, it is time to move on to setting up the carb.

    Baseline the carb by turning in the bleed screws on the front of the carb all the way in until lightly seated. Now back them out 1.5 turns. Connect the vacuum gauge to a port that supplies manifold vacuum ( this will have a high reading at idle and will fall towards 0 when you rev the motor). Start up the car and read the gauge, you should have between 14-21 inches of vacuum at idle depending on your cam. If the car will not stay running, back out each bleed screw 1/2 turn until the car will idle (If you have to back them out more than 3 1/2-4 turns, your metering rods are too small and will need to read up on how to change them, or pay someone to do it for you). Pick one bleed screw and slowly turn it in until the engine starts to stumble. Then back it out until the vacuum reading peaks. Turn the screw out 1/2 additional turn. Repeat this for the other bleed screw. Readjust your idle to 800 rpm and you should be ready to roll. Disconnect your tools and plug the vacuum line back to the distributor.
    thanks alot, good info. I will see if i find out the cam specs before i do anything

  4. #24
    Rockin the Ruckus! 02Sweet's Avatar
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    Quote Originally Posted by bamaz28 View Post
    say what you want but we cranked out over 50-75 sbc no problems
    Im not putting down that method I have done it a few times to my older trucks, but a timing light has always yielded better results for me

  5. #25
    Junior Member cycowrencher's Avatar
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    You really do not need the cam specs to tune the car correctly. However, if the cam is too big for the motor it will run like ass no matter how you tune it. Do what I posted, and if it still runs badly, search for the cam specs to find out if it is too much for the motor. If you drive that car part time, you need those tools anyway,just to keep it running. It sounds like it ran fine before, so it most likely needs a tune up. Plugs, Wires, Cap, Rotor, and points if it still has them. You may just have corroded points causing the whole issue.

    I put a Crane 276 with .450 lift in the 305 that used to be in my 81. It was my first cam swap over 12 years ago. The motor had nothing until 3500 rpm and would pull to 7000. I had a 4 speed at the time, so it was not too much of a dog down low. That motor was very short lived because of the cam. It would not idle below 950 rpm and at 950 it was still "lumpy".

  6. #26
    Rodzilla Tha Cavity Filla zero_proto's Avatar
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    Quote Originally Posted by cycowrencher View Post
    You really do not need the cam specs to tune the car correctly. However, if the cam is too big for the motor it will run like ass no matter how you tune it. Do what I posted, and if it still runs badly, search for the cam specs to find out if it is too much for the motor. If you drive that car part time, you need those tools anyway,just to keep it running. It sounds like it ran fine before, so it most likely needs a tune up. Plugs, Wires, Cap, Rotor, and points if it still has them. You may just have corroded points causing the whole issue.

    I put a Crane 276 with .450 lift in the 305 that used to be in my 81. It was my first cam swap over 12 years ago. The motor had nothing until 3500 rpm and would pull to 7000. I had a 4 speed at the time, so it was not too much of a dog down low. That motor was very short lived because of the cam. It would not idle below 950 rpm and at 950 it was still "lumpy".
    will do

  7. #27
    Junior Member louisianagulf's Avatar
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    1955 chevy belair

    First thing you do is crank it cold and run it for about 10 - 15 seconds and shut off. Feel each cylinder tube for heat. Change out the plugs on the cooler or cold ones. Then go from there. You would be suprised how a cylinder or two down can affect the running of an eight cylinder

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