Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

454 back fires at 1/2 throttle or more

Discussion in 'The Garage' started by nemesis_pyros, Jul 12, 2005.

  1. nemesis_pyros

    nemesis_pyros 1/2 ton status

    Joined:
    Mar 24, 2004
    Posts:
    229
    Likes Received:
    0
    Location:
    Winnipeg, Manitoba
    ok so I took my truck out after about 2 years of not being driven on the street. (it was started and moved from time to time) Well it runs pretty good but when I get on it at 1/2 throttle or more it starts to back fire through the carb like crazy. Like i said when I parked it, it worked fine and we did start it a few times to move it and all was well. The only thing that appears wrong with it is I need to adjust some of the rockers as they are making a bunch of noise, but I don't think that pertains to this problem.

    454 in a 49 chevy p/u with a th400 and a 10bolt with 3.08s


    thanks
    Brent


    oh I have tried adjusting the timing from retarded to advanced and it makes no difference.
     
  2. thatK30guy

    thatK30guy 1 ton status Premium Member

    Joined:
    Jan 12, 2001
    Posts:
    32,076
    Likes Received:
    55
    Location:
    .
    Vacuum leak? :confused:
     
  3. k5guyva

    k5guyva 1/2 ton status

    Joined:
    Oct 26, 2003
    Posts:
    165
    Likes Received:
    0
    Location:
    Southeast VA
    Could be distributor vac advance probl. There are some springs and weights in there.
     
  4. nemesis_pyros

    nemesis_pyros 1/2 ton status

    Joined:
    Mar 24, 2004
    Posts:
    229
    Likes Received:
    0
    Location:
    Winnipeg, Manitoba
    Good point didn't think to check the distributor advance wieghts, I'll do that this evening and see how things go. No vacum leaks as far as I can tell. But I'm gonna go over it thoughly this evening. thanks guys i'll keep you informed
     
  5. thor

    thor 1/2 ton status

    Joined:
    Aug 20, 2003
    Posts:
    512
    Likes Received:
    0
    Location:
    Wa
    If it's an HEI check the wires from the inductive pick up, they like to crack from where the vacuum advance moves the assembly and will cause this. have to change out the pick up if they are cracked.

    It could also be an intake valve hanging open. a compression test will catch this. SeaFoam makes a terrific product for this, pour one through the carb while running, add a second to your oil....
     
  6. diesel4me

    diesel4me 1 ton status Premium Member

    Joined:
    Jul 24, 2003
    Posts:
    17,577
    Likes Received:
    943
    Location:
    Massachussetts
    might be..

     
  7. sweetk30

    sweetk30 professional hooker Premium Member

    Joined:
    Nov 1, 2004
    Posts:
    25,549
    Likes Received:
    543
    Location:
    horseheads , ny 14845
    same problem with my 454 was bad cam. flat lobes. ran great till more than 1/2 gas . will almost be sure worn out cam. the bbc eat them more than sbc.
     
  8. nemesis_pyros

    nemesis_pyros 1/2 ton status

    Joined:
    Mar 24, 2004
    Posts:
    229
    Likes Received:
    0
    Location:
    Winnipeg, Manitoba
    New Problem, Old problem fixed thanks for the Help.

    Fixed the rockers, runs nice and quiet now :D . Also found a vacuum leak at the vacuum advance port on the Distributor. Runs much much better now! just needs some tuning.

    I got a new porblem now the bushing in the tail shaft on my TH400 is chewed and it ends up walking back on the yoke and pushing the output seal out of the tranny allowing me to lose all my tranny fluid. Question is can I just clean up the yoke a little if its scored a bit, then get the bushing and put it in myself with the tranny in the truck. I talked to a shop and they said i had to take the tailshaft off and the bushing had to be perfectly seated. The out put seal is brand new and so are the u joints. The yoke wobbles so bad that it feels like really bad u joints.
     
  9. dave_90_blazer

    dave_90_blazer 1/2 ton status

    Joined:
    Jan 1, 2004
    Posts:
    688
    Likes Received:
    0
    Location:
    Melvindale, Michigan
    one other thing to check, take your distributor cap loose and see if you can wiggle the rotor, also check the pickup reluctor wheel, ive seen both worn out and loose, causing reallly wierd drivablity issues
     

Share This Page