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Carb and or Timing issues

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Hossbaby50, May 31, 2003.

  1. Hossbaby50

    Hossbaby50 3/4 ton status

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    I am having a problem with my truck. My truck starts to stumble at idle after a little while. I don't seem to have a problem when I am cruising, but when I am at idle it acts like it is missing sometimes or loading up with fuel or something.

    When I sit at a stoplight at idle it will be fine for 30 seconds or so then I will start to get a stumble or miss. The RPM's jump around and it will stumble off idle when it starts missing like that unless I start off the line with very little throttle. If I raise the RPM a little by giving it some gas with the brake on it starts to go away or not happen as much. Any ideas?

    I know my timing isn't right (which is a whole nother issue), but it is set by ear. I did it with the timing both advanced and retarded a fair amount. It doesn't seem to be as bad with the timing more advance though.

    Any help or advice is appreciated. I need to get it running better for the trail run next weekend. Thanks

    Harley
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    An "intermittent" stumble or miss like that makes it sound like an electrical issue.

    You know, bad plugs, bad wires, coil, dist module, something along those lines that may work better with more voltage through the system, or more heat. I wouldn't *suspect* it to be mechanical, as something like a bad gasket, carb out of tune, so on, *should* be consistent at idle.

    Only mechanical problem I've seen that caused a miss at idle on my truck, and somewhat randomly, was messed up mechanical advance weights.

    Unfortunately there can be millions of "rare" causes for this problem I'm sure, hopefully others can chime in with "loading up at idle" stories and what the problem was for them
     
  3. 87GMCJimmy

    87GMCJimmy 1/2 ton status

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    I had a similar problem with my truck years ago. It turned out to be the distributor. If the 85 and 87 are the same I have a spare one that you could borrow for a week or so to see if it's the problem. I would image it's an electrical issue. My experience with carbs is that they work or don't. Intermittent problems have been always been electrical. Either way good luck, problems like this have always been a PITA for me to find.

    Mike
     
  4. wrathORC

    wrathORC 1/2 ton status

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    Is it hard to start after it's been hot then sits for about twenty minutes?

    Does it do it at high rpm as well (above 3500rpm)?
     
  5. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    First off I would see if someone you know has a timing light. The movement of the distributor a verry little amount by hand moves the timing an awful lot. Make sure your plug wires are not touching the exhaust and are in good shape, as well as cap rotor and plugs. It is easier to troubleshoot when it is all set to stock ( APPLIES TO STOCK CAMSHAFTS ).
     
  6. pilgrim

    pilgrim 1/2 ton status

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    I just figured out that my distributor was causeing me all kinds of troubles. My rig was hard to start or wouldn't at all when it was hot. Turned out to be the little piece of thin metal on the rotor that contacts the distributor. it would "bend" away from contacting it when hot /forums/images/graemlins/angryfire.gif, so i bent it back up and bam, truck start....

    all this talk about distributor's is makeing me think that some of my "carb issues" could be comeing from that piece of poo thing that ACCEL made....
     
  7. Hossbaby50

    Hossbaby50 3/4 ton status

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    It only stumbles when it is idling (650RPMish) and a little higher. Over 1000 RPM and it won't happen. When it is below 1000rpm it will do it, but the closer to 1000 it is the longer it takes the problem to start.

    I can't time my motor by anything except for the ear. Apparently when the Chevy dealer installed my crate motor they installed the wrong damper. So the timing mark doesn't line up with the timing scale on the timing chain cover.

    My ignition system is MSD. I have a factory distributor base but the cap, rotor, coil, wires, and ignition box are all MSD. The plugs are less then 1 month old (Champion Truck plugs gapped to .053).

    I was also thinking that the problem might be in the vacuum system or fuel pump. I was thinking the vacuum may drop too low at idle and start to make the motor run like crap, or the fuel pump may not flow enough fuel. But the fuel pump is under 4 months old, and the vacuum lines are only a few years old.
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    [ QUOTE ]
    It only stumbles when it is idling (650RPMish) and a little higher. Over 1000 RPM and it won't happen. When it is below 1000rpm it will do it, but the closer to 1000 it is the longer it takes the problem to start.

    I can't time my motor by anything except for the ear. Apparently when the Chevy dealer installed my crate motor they installed the wrong damper. So the timing mark doesn't line up with the timing scale on the timing chain cover.

    My ignition system is MSD. I have a factory distributor base but the cap, rotor, coil, wires, and ignition box are all MSD. The plugs are less then 1 month old (Champion Truck plugs gapped to .053).

    I was also thinking that the problem might be in the vacuum system or fuel pump. I was thinking the vacuum may drop too low at idle and start to make the motor run like crap, or the fuel pump may not flow enough fuel. But the fuel pump is under 4 months old, and the vacuum lines are only a few years old.

    [/ QUOTE ]
    Vacuum is actually highest when at idle becuase the butterflies are shut in the carb.
    Choke not full opening can cause this, EGR problems can cause this. EGR should be off at Idle. It comes on about 1500 RPM. The fact that it will idle then messes up leads me to think it's a choke or possbile even the solonoid in the carb causing this. Most likly the choke. THe heating elemnets only last a couple years is my experiance. Pull the top off the air claner and make sure the choke is all the way open once the the truck is warm.
     

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