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timing help...(25degrees Before) not right!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BIGRIG, Oct 29, 2001.

  1. BIGRIG

    BIGRIG 1/2 ton status

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    Ok to make the truck shut off and not deisel it has to be at like 20deg. before, but then it doesnt run right and pings when i get on it. If I get it at like 8 before it deisels when I shut it off but runs good when on it...question is what does advancing the cam or retarding the cam 4 degrees do? and if you have any other suggestions. It's a 350 .30 over 400 crank, erson cam 9 to 1 compression i think i need to check it.

    Thanx

    Chris

    MY DRINKING TEAM HAS A FOUR WHEELING PROBLEM![​IMG]
     
  2. hammer

    hammer 1/2 ton status

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    check your carb the chock it might be sticking, It will make that happen
     
  3. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Advancing or retarding your cam timing just moves the power band up or down...thats an over simplification obviously but it does not affect 'Deiseling' one way or the other. Unburned fuel and small hot spots (usually carbon deposits) can contribute to deiseling. If the idle is set too high, carb really rich o the idle circuit, throttle blades not closing properly on shut down, all cause deiseling. Until you find the problem shut it down in gear if it's an automatic, for a standard shut it off in gear and let up on the clutch to help kill the motor.

    I'd check your carb...

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     
  4. Sparky

    Sparky 1/2 ton status

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    350 with 400 crank? In other words its a 383? What heads are on it? What kind of gas are you running? You probably need at least 89 octane with that compression unless you have vortec or some other really cool heads that let you run higher compression without pings. As far as advancing or retarding the cam, it can give you slightly better horse power or torque, but usually has more of an effect at higher RPM's. For a 4x4 or truck that isnt mud or street racing just leave the cam at 0 degrees. In order to keep it from dieseling around 8 degrees make sure you dont have any vacume leaks and make sure the carb/fuel system is in good shape and not makeing it lean. Check and make sure you have the proper heat range plugs. Check or replace your cap and roter, plugs, and plug wires. The list could go on, but chances are those are the most likly things. Start with that and if the problem persists ask some more specific questions. Hope this helps

    Sparky

    When all else fails... Check the blinker fluid.
    78 K-5
     
  5. Sparky

    Sparky 1/2 ton status

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    Hey trusty,

    I'm not acusing you of anything here, and correct me if I'm worng, but dosent it have to be a lean mixture in order to cause dieseling? A rich mixture would cause a lower temperature combustion right? The more air you got the hotter the combustion. In order for it to diesel it has to get hot enough with a high enough compression to cause ignition without a spark plug fireing. Thus a lean mixture would cause dieseling not a rich one.

    Sparky

    When all else fails... Check the blinker fluid.
    78 K-5
     
  6. BIGRIG

    BIGRIG 1/2 ton status

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    You all amy have hit the jackpot! The carb is off my orig Q-jet off my 305...I knew it ran lean but never even thought about it causing it to diesel. duhhh. That may be one hell of a lead to follow....I've got a TPI and was trying to make the carb last tell I get it together. The cam adv. though I did not know! Thanks.

    Chris

    Gotta love this place!



    MY DRINKING TEAM HAS A FOUR WHEELING PROBLEM![​IMG]
     
  7. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Caught me thinkin backwards...[​IMG] Every vehicle I've had that deiseled smelled real bad of fuel...

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
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  8. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Rene was correct (in a way). Yes usually dieseling is caused from lean mixtures (causing the engine to run hot), but a poorly cooled motor (bad water pump, clogged radiator) combined with rich fuel mixture causes carbon deposits which create hotspots and will ignite the excess fuel on shut-off. It is less common, but can happen. What does the temp guage read when the motor is being shut down?

    See my rig at <a target="_blank" href=http://coloradok5.com/gallery/Leadfoot>http://coloradok5.com/gallery/Leadfoot</a>
     
  9. The cam should actauly be set with a degree wheel to the cam's specs,thses numbers should be on the spec sheet that came with the cam.A simple vacume leak can cause the same problem.Just my $.02.Good luck
     
  10. 1986Blazer

    1986Blazer 1/2 ton status

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    What about something more simple like the balancer gone bad. Maybe it has slipped a few degrees off because of a bad rubber bushing? Just an idea. I had the same prob and had to replace the balancer - I could not get an accurate timing.

    <a target="_blank" href=http://www.geocities.com/keywestk5/KeyWestK5.html>http://www.geocities.com/keywestk5/KeyWestK5.html</a>
    So I says to him, I said, "get your own monkey."
    1986 K5, 350 GM Crate, 700R4, NP208
     

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