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backfire through the carb

Discussion in 'The Garage' started by 85 Jimmy, Aug 3, 2006.

  1. 85 Jimmy

    85 Jimmy Sheepdog Premium Member

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    ok guys, here's the deal. i have a 1985 GMC jimmy with a 305 in it. well yesteday on my way to work it stalled on me and i found that i wasn't getting any spark. i found the problem to be the magnetic pickup in the dizzy, so i pulled the dizzy and rebuilt the whole thing (i got bored at work, and since we had all the parts in stock...) any way. before i pulled the dizzy i marked the rotor location and the base location after i pulled around to TDC like you should do. so i put it all in and it lined up perfect with my marks. well at first crank it ran alittle rough, but since we only work on new vehicles at the hummer dealership, no one had a timing light. it felt fine at work atleast fine enough to get it to my house, i'd rev the motor and it seemed alright, well i pulled it out the shop and put it in drive, i stomped on it and i got a backfire through the carb, so i got home after it was backfiring all the way home, and i looked for a timing mark on the timing cover, THERE'S NO TIMING MARK?!?!?! i guess the PO decided he didn't need it so he took it off. well i decided i'd time it by ear, everything i do i still get a backfire through the carb...

    so heres the problem summed up. i'm getting a backfire through the carb when the engine is under a load only. what should i do to fix the problem???
     
  2. broncoman6524

    broncoman6524 1/2 ton status

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    this happened to me the other day, 1st check you rocker arms. Id assume you know how to adjust them. 2nd my buddy said it may have been my *mechanical* timing IE off by like a tooth and pre-igniting or firing too late. Good luck.

    It sounds kinda like a ricer (realy loud and blatty) when you are about to hit you shift points right?
     
  3. justhorsinaround

    justhorsinaround 3/4 ton status

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    It ran fine right before the distributor issue?
     
  4. 85 Jimmy

    85 Jimmy Sheepdog Premium Member

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    well since all i did was pulled the dizzy and rebuilt it i don't think it could be the rocker arms. and do you mean that my distributor gear could be off by a tooth? if so my marks wouldn't have lined up when i put it back in... right?
     
  5. 85 Jimmy

    85 Jimmy Sheepdog Premium Member

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    yep
     
  6. broncoman6524

    broncoman6524 1/2 ton status

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    exactly i know it didnt make sense to me either but when i put my new intake on and then replaced my dist. my lines didnt realy like up perfectly either. :dunno: Only thing was mine wouldnt run, actually it did but it was 180 degrees out. does you truck feel like its got no power, coming from a stop but once you get going its fine?

    The same thing happened to my truck and i thought to myself why the hell were the rocker arms loose. (all i had done was mess with the timing and go play in some mud:rolleyes: ) If you can hear a clickin noise from one or both sides of the motor it is more that likely something in your valvetrain.
     
  7. justhorsinaround

    justhorsinaround 3/4 ton status

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    As a quick try, retard the thing alot and see what happens. I have in the past thought I had everything lined up perfectly only to find out I was a tooth or two off.
     
  8. 85 Jimmy

    85 Jimmy Sheepdog Premium Member

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    yeah it doesn't have any power from a stop. there's no tapping or clicking coming from the motor

    i retard it and i advanced it and it still does the same thing, but i'll try it again tomorrow at work
     
  9. justhorsinaround

    justhorsinaround 3/4 ton status

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    Maybe just maybe you had two gremlins pop up at the same time. You have compression testers at work?
     
  10. broncoman6524

    broncoman6524 1/2 ton status

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    your 180 degrees out. i dont realy remember what that means or how to fix that **** i feel stupid as hell. lol

    im pretty sure that it means that your timing is off by like 2-3 teeth. crank your motor over until the mark on the harmonic balancer is where you indicator *should* be . before you take off the dist cap take a sharpee and mark on the #1 cylinder plug wirethingy on the cap and on the actualy dist metal bottom. Pull the dist. make sure that when you drop it back in the rotor is aligned close to the mark you made on the dist. Try that, its what my mechanic neighbor did and it fixed it.
     
  11. broncoman6524

    broncoman6524 1/2 ton status

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    btw you can elimate the valvetrain:D :rolleyes: lol
     
  12. 85 Jimmy

    85 Jimmy Sheepdog Premium Member

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    i just got finished driving it and there 's no pattern, it'll backfire SOMETIMES when i come from a stop, and it'll do it SOMETIMES when i'm just going down the road cruising, it never did it at WOT though

    i'll just ask the guys at work...
     
  13. 85 Jimmy

    85 Jimmy Sheepdog Premium Member

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    i feel like an idiot now.

    i accedintally got the #3 and #5 plug wires mixed up :doah: , swapped them and now is running better than before it failed on me
     
  14. BackDoor-Banditt

    BackDoor-Banditt Registered Member

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    i have a 87 S10 blazer that just did this to me trust my on thin=s theres only two things that can cause this one it jumped time, or two (this ones ****ed up but its true) put your air breather back on, mine worked fine after i put the air breather on it worked like a champ
     
  15. Thunder

    Thunder 3/4 ton status

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    I dont see how there is any way getting your fireing order right could have fixed your truck. The above post says there only 2 things that cause your problem.
    You must have put your air breather on and didn't tell anyone. I wear my air breather all the time:D
     

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