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Carb Backfire? Engine guru needed!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by NMJImmy, Jul 26, 2002.

  1. NMJImmy

    NMJImmy Registered Member

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    I was looking at a '78 Blazer yesterday that someone had for sale cheap, but when running it would backfire through the carb. He said that when he installed the dist he must have put it 180 degrees out, therefore causing the backfire. Is this true, if not what else would cause it to do this? What can this damage?

    It just makes me leery as to why he wouldn't fix it if he is trying to sell the Blazer. Other than that the engine seemed to run fine.

    Any input would be appreciated, thanks.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    180 degrees out I don't believe it will run at ALL.

    The timing could be *off* though, when mine was messed up (advance weights stuck) when I tried to give it gas, it would stall, then pop (backfire) through the carb.

    How does it start? Really advanced timing is easy to tell by how hard it is to turn over...if the engine doesn't "spin freely" but sounds like the starter is having a hard time, bogging down as it cranks, its probably too far advanced.
     
  3. NMJImmy

    NMJImmy Registered Member

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    The engine runs good, sounds smooth, started right up. The only thing was the steady backfiring through the carb. He had said that he had just did a top end rebuild, could they have screwed something up on an intake valve causing the backfire?
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    I hope someone else has an idea, because I don't have anything concrete, sorry. Steady backfire but runs good? Maybe a fuel drip inside the carb or something?...
     
  5. bklynlifted

    bklynlifted 1/2 ton status

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    sounds like timing . break out the timing light to verify it's OK next pull the cap check things /forums/images/icons/smirk.gif out.
     
  6. 1979Jimmy

    1979Jimmy 1/2 ton status

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    Im with timing...
     
  7. HarryH3

    HarryH3 1 ton status Author

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    If it starts right up, then backfires all the time, then an intake valve is probably not closing all the way. It could be something as simple as a rocker arm that needs to be adjusted, or as bad as a burned valve. I'd try to talk him WAY down on his price, since you'd be taking the risk of needing to go inside the engine. Or just pass it up and wait for a better truck to come along. /forums/images/icons/cool.gif

    Oh yeah, the engine won't start with the distributor installed 180 degrees out.
     
  8. joker89blazer

    joker89blazer 1/2 ton status

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    Everything i can think of would be internal,like cam timing,rockers,bad valves.The guy said he just done a top in rebuild but thinks he got the timing wrong and he can not fix? I don't think I would want a motor that was rebuilt by a person who could not set base timing.If the rest of the truck is in great shape, and you had your eyes set on a 383 stoker, it might be what you want
     
  9. Wally81k5

    Wally81k5 1/2 ton status

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    wooooooooo!!! Be careful!! I just lost $800 dollars over the smae problem. Bought a jimmy, ran for 2 days, started backfireing out the carb, looked inside... changed some rockers and push rods. Turns out the cam was worn out and made it do exactly what you are talking about!! Have a look!
     
  10. NMJImmy

    NMJImmy Registered Member

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    Thanks for all the replies, I think I'll take everybody's advice n' run. I was just looking for something cheap to play with and this could just turn into another headache.

    Thanks again!!
     

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