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Explosion through the carb

Discussion in '40- & 55-Series Tech' started by baldboy, Aug 23, 2006.

  1. baldboy

    baldboy

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    Soooo.... I got my linkages connected correctly, carburetor back on the 78 2F motor, go to start it, runs really fast and then BOOOOM!!! like an atomic bomb (it was LOOOOUUUUUUD!) it explodes through the carb.

    When I originally took the carburetor off last week 90% of the emissions hoses broke off so I plugged them in a futile attempt at completion of my simple carb project.


    It was LOUD.... A lot of my neighbors came down their driveways to see what happened......


    So, diagnosis..... vacuum leak?, Missing emissions problems?, Something else?


    Thanks for any suggestions.... I know I have had a lot of questions about this carburetor but I need to get this thing going properly and I am pretty ignorant as far as aspiration systems go.
     
  2. Fast Eddy

    Fast Eddy

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    Sounds like a sparkplug went off with the intake valve open. Timing? Plug wires in the right order?
     
  3. projektdotnet

    projektdotnet

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    what drives the timing on these (gear, chain, belt)?
     
  4. Degnol

    Degnol

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    Gears. But check to see that your timing isn't off by 180*

    GL

    Ed
     
  5. projektdotnet

    projektdotnet

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    I was gonna say cause my friend had a belt go out in his chivette and it was spitting raw gas out the top of the carb.
     
  6. 65swb45

    65swb45 Supporting Vendor

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    Need more info.

    Was the truck running ok before you took the carb off?

    Did you take anything else off besides the carb and the emissions?

    Did you rebuild the carb?

    Did you make any provisions for the power valve to keep it from dumping gas in at idle?

    Running fast? Are you sure you got the return spring back on the carb?

    Stock dizzy? Where did you plumb the advance diaphram? Directly to the intake?

    Theory: Full vacuum advance at idle and no provision to keep the power piston retracted.....combined to let a LOT of fuel into the cylinder and be ignited by fully advanced timing. Disclaimer: only theory I could come up with without more info from you.

    Best

    Mark A.
     
  7. baldboy

    baldboy

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    The truck ran strong before I took the carb off but would not idle due to debris in it.

    I didn't take anything else off.

    It is a stock distributor.

    All linkages and springs double-checked and in place.


    I thought I connected the advance diaphragm as was it originally. I will have to check it tonight.

    Thanks for the input and let me know if you have any more thoughts on it.
     
  8. honk

    honk

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    This follows your overrevving of the other thread?

    If so, maybe you'd better take off the valve cover to check for any bent or out of place pushrods and watch the valve gear for bent or sticking valves as you crank the motor without letting it start.
     
  9. Pin_Head

    Pin_Head

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    Popping back through the carb is a sign of lean fuel mixture, but I wouldn't describe it as like an "atomic bomb".

    If the only thing you have fiddled with is the carb, then chances are that that is the problem.
     
  10. camcruiser13

    camcruiser13

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    my buddie had his off by 180 and it did the whole atomic bomb blast and it blue his vavle cover off, it was scary.
     
  11. 65swb45

    65swb45 Supporting Vendor

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    Another thought. If you did not hook up a vacuum source to the throttle positioner, then the linkage would not retract out of the way once the engine started, and would be unable to reach idle speed.

    If you de-smogged, where did you source vacuum for the throttle positioner?

    Mark A.
     
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