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auto vs manual carb tuning? WTF??

Discussion in 'The Garage' started by 78Suburban, Jan 16, 2006.

?

What should I do?

  1. Put the old electric choke carb back on and tune it.

    6 vote(s)
    27.3%
  2. Put my old motor's dizzy and plug wires on.

    2 vote(s)
    9.1%
  3. Find a way to convert this carb to manual choke.

    4 vote(s)
    18.2%
  4. Get nekkid in front of a backfiring carb.

    10 vote(s)
    45.5%
  1. 78Suburban

    78Suburban 1/2 ton status

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    I haven't been on ck5 in like a week cause my net was down. I have been trying to get my truck running correctly so that I can go wheeling, but have been having some bad luck. Here's the story:

    I pulled my old 350 motor w/ qjet out of my burb. This carb had a little heat coil that bolts to the manifold that makes the choke work. This truck also has a th400.

    I swapped in a 350 from a manual tranny k5 (origionally from 73 camaro). This motor has an electric choke. This motor also had EGR, but I pulled and blocked it. The PO had plugged a bunch of other ports in the carb.

    I gapped all the plugs to .035 and fired her up and set the timing to 8* BTDC. She idles beautifully. I tried to drive it a little ways and it chokes like crazy!! It also wants to idle really low and cut out when I turn on the AC. It backfired through the carb when I tried to drive with much throttle at all.

    I figured that the carb was just not tuned right since it came from a straight shift with no AC. So I pulled my Q jet from my old motor (the one with the heat coil choke thing). I got a new gasket and bolted that carb up to the motor. There was no where to bolt the little heat coil thing , so I decied to just take the 2 screws from the choke plate and see if she would run with no choke at all. No when I try to crank it, it idles crappy, tires to cut out, and backfires through the carb. I suppose this could be from removing the choke. It's like 60 degrees outside right now. I'm really at a loss as to why it doesn't run.. I wonder if there is a way to convert it to manual choke? Aren't some people running with no chokes? I just can figure why it won't run.

    What should I do? If anyone can help me figure this one out, I'll owe you forever!! This little issue is all that stands between me and getting to wheel my burb.
    Thanks so much in advance,
    James :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow: :bow:
     
  2. big94gmc

    big94gmc 1/2 ton status

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    There isn't an option for me to select.... TBI!!!

    (So I'm nekkid.)
     
  3. gmtech954

    gmtech954 Registered Member

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    i would check your timing and make sure your vac advance is connected properly to a ported vac source
     
  4. 78Suburban

    78Suburban 1/2 ton status

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    Its connected and timed to 8* BTDC.. idles good, just chokes like crazy under throtttle......... I'm considering swapping the electric choke carb back on and swapping out the dizzy.... to see if the ignition is my problem. I just hope to have it up and running soon. Is my timing no correct, or should the plug gap be different than .035? I timed it with the vac advance line disconnected from the dizzy and plugged at the carb.
    Any more ideas or suggestions would be AWSOME.
    thanks,
    James
     
  5. BadBob

    BadBob 1/2 ton status

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    make sure the outer ring on your balancer hasn't slipped around on you
     
  6. 78Suburban

    78Suburban 1/2 ton status

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    you're talking about the timing tab being out of line? or what?....... it does seem to be in a different place (more to the right) than my old motor... but I figured that was just because my old motor had AC so they came in a different position from the factory.
     
  7. Triaged

    Triaged 1/2 ton status

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    I voted for nekid. Just remove the choke.
     
  8. 78Suburban

    78Suburban 1/2 ton status

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    I took off the choke plate (removed the 2 screws that hold it to the bar across the top of the carb) Now it doesn't even really want to start. And it backfires through the carb.. At least the old electric choke carb would crank and idle.. I'm really aggrivated at this truck.. I'm gonna put the electric choke carb back on and swap in another dizzy and see what happens..
    I'm also starting to wonder about the timing tab and if its in the correct position... There are so many variables that could be causing my problems.. Wish I had someone who knew what they were doing to look at it for me.
    This thread has had some long replies.. like one sentance each. lol
    thanks,
    James
     
  9. Triaged

    Triaged 1/2 ton status

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    Can you describe how you hooked up and timed the dist?

    Did you pull off and plug the vacuum advance when you set the timing to 8*?

    Is the vacuum advance hooked up to constant (below the butterflies) or ported (above the butterflies) vacuum?

    I don't think you have a carb problem at all...
     
  10. 78Suburban

    78Suburban 1/2 ton status

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    out of timing 180*?

    after a long IM conversation with Muddytazz I'm starting to think that its out of timing 180*.. since it runs good at idle but goes crazy in upper RPM's.. guess I just gotta pull the dizzy and retime her
    thanks,
    James
     
  11. Triaged

    Triaged 1/2 ton status

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    If it was 180 out it wouldn't start or run at all!

    If however the advance had vacuum to it when you timed it to 8* you would LOOSE timing when you loose vacuum and it would start backfiring out the intake.
     
  12. 78Suburban

    78Suburban 1/2 ton status

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    the vaccume advance was plugged at the carb and unhooked from the dizzy.
     
  13. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    Check the choke linkage under the round choke thingy. It may be sticking or the choke could need adjusting. Also I think A/C equipped trucks came with an high idle adjustment vacumn thingy (on the drivers side maybe) to compensate when the a/c was on. Does the carb look like the one that was on your truck minus the electric choke? It could be the timing but I don't know. I do know that the carb worked flawlessly in the truck, I ran it at 75 to 80 mph with no problems. Hang in there James you'll get it right. Nothing like the satisfaction of a job well done and the knowledge you gain from it. I just spent 2 weeks working out the bugs with my SM465 swap, pulled the tranny 3 times and reinstalled.
     
  14. k5rocker

    k5rocker Registered Member

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    OK, let's start with the basics.
    1. Is this a known good engine? You didn't say you heard it run or drove it before you installed it in your truck. There may be dead lifters, low compression, etc.
    2. Make sure the RING on the balancer (the part that has the timing groove in it) still points to exactly TDC (0 degrees) on the scale when #1 piston is at TDC (check this by sticking a wooden dowel in the spark plug hole and "feel" the piston come up and peak out while slowly turning the crank with a breaker bar. Compare highest dowel reading to timing marks.
    3. If it is in proper time, check for vacuum leaks. If none found, CHECK COMPRESSION.
    4. Take 2 asprin and call me in the morning. I don't think the carb is the problem either, but you can play with the choke, maybe force it open when the engine is warm and wire it in place and see if it drives any better. Hope this helps, will keep an eye on this thread.
     
  15. 78Suburban

    78Suburban 1/2 ton status

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    If John says the engine is fine, then its definitely fine.. its just some of my handywork.. lol...... I'm almost to the point of putting money on the dizzy being 180* out.......
     
  16. clarkjw24

    clarkjw24 1/2 ton status GMOTM Winner

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    Thanks James. Yeah, if I wanted to screw someone, I don't believe I would have drove 7 hours one way to deliever an motor for free. So #1 on that list is ruled out.

    You'll get it, don't worry.;)
     
  17. 78Suburban

    78Suburban 1/2 ton status

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    timing...........

    I'm still a little confused about timing it. If its not 180* off, but only 1 or 2 teeth off, would it still be saying 8* BTDC with the light? Or is is just idling ok but doing bad under throttle from being 180* out? Right now I'm thinking of turning the motor over till its says TDC on the tab and the rotor is pointed at #1 cylinder.. then turning it over one more crank, and pulling the dizzy out and aiming it toward #1cylinder,,, since I'm thinking its currently 180* out.. am I making any since? Or does everyone just want me to get nekkid in front of my backfiring carb? :eek1:
    thanks,
    James


    PS: I'm wondering if 8* BTDC and .035 plug gap is correct for this motor. It was for the stock motor in the burb, but this motor is origionally from a '73 camaro... I'm wondering if I don't need to set it at 12*BTDC, or maybe 4* BTDC.. who knows......... anybody got any numbers on this in a service manual?
     
  18. Triaged

    Triaged 1/2 ton status

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    Just ditch the timing light and put the dist where the engine wants it. Keep advancing it till it pings on acceleration up a hill and back it off just a bit.

    FWIW my engine likes to idle at about 30* (yes that is thirty degrees BTDC) with the vacuum advance hooked up to full manifold vacuum.
     
  19. bigbadchev84

    bigbadchev84 1/2 ton status

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    double and triple check your timing, and play close attention to your #5 and #7 plug wires they fire right after each other so it could idle fine but when it revs up it would cause it to fire with valves open....just not as noticable at low rpms
     
  20. zeroz400

    zeroz400 1/2 ton status

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    Ive gone through the 5&7 wire problem before, it will backfire through your carb so definately look into that. Try setting your timing again, you still could be a tooth off. Maybe your vacuum advanced is no good? If you have another distributor you could try tossing that in.
     

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