Welcome to Club Hot Rod!  The premier site for everything to do with Hot Rod, Customs, Low Riders, Rat Rods, and more. 

  •  » Members from all over the US and the world!
  •  » Help from all over the world for your questions
  •  » Build logs for you and all members
  •  » Blogs
  •  » Image Gallery
  •  » Many thousands of members and hundreds of thousands of posts! 

YES! I want to register an account for free right now!  p.s.: For registered members this ad will NOT show

 

Thread: Well, I've tried most everything.
          
   
   

Reply To Thread
Page 1 of 2 1 2 LastLast
Results 1 to 15 of 19

Hybrid View

  1. #1
    SBC Maro's Avatar
    SBC Maro is offline CHR Member Visit my Photo Gallery
    Join Date
    Dec 2005
    Location
    Lompoc
    Car Year, Make, Model: 1970 Chevy Nova
    Posts
    73

    Well, I've tried most everything.

     



    This is killing me! I have a 355 that I just CAN NOT floor without fireball-out-the-carb backfires.

    I've tried 2 distributors, 2 coils, new plugs and wires (Plugs gapped). 5-6 different initial timings with a mix of no vac advance, ported, and full. Tried 3 different carburetors (600, 650, 750 double pumper) and I just can't get this shaken out. This is starting to absolutely drive me nuts.


    The car runs great it idle (This is a 355 with Dart heads and a very mild cam) with about 8-12 degrees of initial timing, on full vacuum advance. Yea, I disconnected the vacuum advance when setting initial

    As soon as I peg the car though, with an exception of doing so at a very high RPM, the car will backfire out the carburetor, and shut down. If I lean into the throttle, and avoid pegging it, it works out, and picks up very well.

    I thought maybe I was running lean, but with a 750 mechanical secondaries double pumper? I'm out of ideas here.

    NOS is the only way to void your insurace, warranty, and birth certificate with one push of a button.

  2. #2
    SBC Maro's Avatar
    SBC Maro is offline CHR Member Visit my Photo Gallery
    Join Date
    Dec 2005
    Location
    Lompoc
    Car Year, Make, Model: 1970 Chevy Nova
    Posts
    73

    I'll get out there and take a look, Give the neighbors a few more minutes of precious rest before I start banging around out there

    NOS is the only way to void your insurace, warranty, and birth certificate with one push of a button.

  3. #3
    500caddy is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2007
    Location
    det
    Posts
    205

    check for vacuum leaks around the intake.. if you have power brakes make sure the booster is not leaking vacuum it will cause a lean pop. the next thing is are you running a mech or hyd cam?? to much preload on a lifter will cause it to. just a base line put as much initial timing you can 20deg or more is fine total 38deg have all the timing in before 2500rpms. did you make sure the timing pointer was dead on??

  4. #4
    500caddy is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2007
    Location
    det
    Posts
    205

    denny, read again i said for a base line tune..i have seen gauges show nothing and it was a vacuum leak. know thats out of the way. three carbs, two dizzy's. if the timing pointer is on then it sounds more like valve timing or to tight of a preload on the lifter only takes one!!! i would lock out the dizzy and set it to 38deg a forget about it and look for the real problem but thats just me..

  5. #5
    500caddy is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2007
    Location
    det
    Posts
    205

    he already said the timing was tried at 8-12. two dizzy's doing the same thing ????????? not likely.. three carbs all doing the same thing again not likely. as for the vacuum gauge if you have no base line and the car idles fine tell me how your going to read it???? the car pops on heavy accel not sure how a gauge will show anything there...i'm not sure way you would run as much int timing as you can?? i run all may sbc with locked out dizzy's. is there something that i don't know about as to way you wouldn't run 20deg of int???

  6. #6
    SBC Maro's Avatar
    SBC Maro is offline CHR Member Visit my Photo Gallery
    Join Date
    Dec 2005
    Location
    Lompoc
    Car Year, Make, Model: 1970 Chevy Nova
    Posts
    73

    Ah! I let this thread go, I haven't been able to get on in a while here.

    I set my initial to 8 degrees, and we're still having the same problems here. I have really steady vacuum, about 17" at idle.

    I'm starting to think it's a valvetrain problem. I want to go through and totally readjust all the valves and see if it helps at all. There is a tick on #5 intake, and I don't know if it's a lifter or a loose rocker arm. I was trying to hot adjust it, and gave it about a 1/4 turn tighter, and the motor seemed to lug a little, so I backed it off, not wanting to do any damage inadvenrtantly.

    Both of these distributors were new, one brand new (the Accell Blueprint Points-style) and a newish HEI with an Accell SuperCap. The HEI was in use on the last motor, and worked like a dream.

    Also, it should be noted that only the 750 is a double pumper, the first 600CFM was an edelbrock, and the 650 was a Holley, non double-pumper.

    I'm leaning towards valve adjustment thought. Thanks alot for the help, You can probably imagine how frustrating it is to have a brand new motor, and and endless supply of problems. Sigh. Hopefully this thing will run right someday

    NOS is the only way to void your insurace, warranty, and birth certificate with one push of a button.

  7. #7
    R Pope is offline CHR Member Visit my Photo Gallery
    Join Date
    Jun 2005
    Location
    Eston
    Posts
    2,270

    Could be a bad plug or wire,too. Even new ones can be NFG.

  8. #8
    C9x's Avatar
    C9x
    C9x is offline CHR Member Visit my Photo Gallery
    Join Date
    Dec 2004
    Location
    N/W Arizona
    Car Year, Make, Model: Deuce Highboy roadster
    Posts
    1,174

    Secondary float level low?
    C9

  9. #9
    fordbeast is offline CHR Member Visit my Photo Gallery
    Join Date
    Mar 2005
    Location
    midwest
    Car Year, Make, Model: 64 galaxie, 68 tang
    Posts
    23

    sbc maro, im thinking timing with quick accelation backfire otherwise carb problems.
    Women are just like cars run'em hard and treat'em rough and they'll eventually leave you stranded

  10. #10
    Racecar100 is offline CHR Member Visit my Photo Gallery
    Join Date
    Jun 2007
    Location
    Lawrenceburg
    Car Year, Make, Model: 1940 Ford Coupe
    Posts
    139

    Plug wires touching each other will cause upper RPM back fire. It will cross fire from one wires to the other. My friend was working on a 37 ford with Buick Nail Head motor did the samething and I seperate all the wires from each other and it stop backfiring.

  11. #11
    SBC Maro's Avatar
    SBC Maro is offline CHR Member Visit my Photo Gallery
    Join Date
    Dec 2005
    Location
    Lompoc
    Car Year, Make, Model: 1970 Chevy Nova
    Posts
    73

    Denny, I'll definitely give that a shot.
    This morning (before I read this) I readjusted all the valves. They were rather loose, although not terribly so.

    It does feel better, but it still likes to pop a little on acceleration, not nearly as bad however. As for the secondary float level, this carb has sightplugs, and the fuel is sitting right at the bottom of the sight window.

    Pope: On the third set of plugs (Bosch, then Autolite AR133s, now Accell 576s) all gapped correctly, and switching to HEI required a new set of wires (Set from the old motor, then Accells for the Points, now Accells for HEI). Sigh.

    Let's pray the you're valve adjustment technique clears this up, I'm getting ready to trade this thing for a 90's ford escort, hah. It would be nice to punch this thing from a dig and light them up

    Thanks so much for all the help, even if I don't fix this glitch, I'm learning a great deal

    -Rob
    Last edited by SBC Maro; 08-26-2007 at 01:07 AM.

    NOS is the only way to void your insurace, warranty, and birth certificate with one push of a button.

  12. #12
    500caddy is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2007
    Location
    det
    Posts
    205

    can i ask what gap your using for the plugs?? i would only put 1/4 preload on the lifters. i never run more then 1/8 to 1/4 on any after market cam and lifters... but if you using anything bigger then a .035 spark plug gap it will do it ever time. you should be using a gasketed nonprojected gaped at .035.plug

  13. #13
    Tohmer is offline CHR Member Visit my Photo Gallery
    Join Date
    Jul 2007
    Location
    American Fork
    Car Year, Make, Model: 1959 Chevrolet Pickup
    Posts
    10

    What kind of break in did you do on the new motor. 15-20 minutes at 2500 rpm usually does it. If the break in was not done well then the cam may be rounding lobes and causing this issue. You can continually adjusy but the lobes will go away. Just a thought.

  14. #14
    erik erikson's Avatar
    erik erikson is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2004
    Location
    clive
    Car Year, Make, Model: BLOWN 540 57 CHEVY
    Posts
    2,878

    Quote Originally Posted by Tohmer
    What kind of break in did you do on the new motor. 15-20 minutes at 2500 rpm usually does it. If the break in was not done well then the cam may be rounding lobes and causing this issue. You can continually adjusy but the lobes will go away. Just a thought.
    If the cam was on it's way out the door it would pop out the intake and exhaust.

  15. #15
    SBC Maro's Avatar
    SBC Maro is offline CHR Member Visit my Photo Gallery
    Join Date
    Dec 2005
    Location
    Lompoc
    Car Year, Make, Model: 1970 Chevy Nova
    Posts
    73

    It's fixed!

    Welp, whaddaya know. It was right under my nose the entire time.

    It turns out that instead of replacing everything, I should have used a little more intuition. Felt retarded, acted retarded, was retarded. Apparently I didn't index my balancer correctly. When I was reading 12* initial, I was getting more like 4 degrees ATDC. My friend's father is a mechanic, and we were just shooting the breeze about the Nova, and we decided to take a look. Cranked the timing up a bunch, drove around listening for knock, and did some minor carburetor adjustments. I punched it at a stop sign, and all hell broke loose.

    This. Nova. MOVES! now that I can floor it, that is

    Thanks for all your help guys, I learned a great deal about tuning while trying to track this problem down. I'm going to go grab some timing tape, get back out the dial indicator set, and degree the balancer correctly. I'm surprised that the car even ran so retarded. When the #1 cylinder was at absolute TDC, the balancer was reading about 16* BTDC, if I remember correctly.

    Again, thanks for your time and suggestions, there is much of wisdom that you can only get from the combined experience of this many people.

    NOS is the only way to void your insurace, warranty, and birth certificate with one push of a button.

Reply To Thread
Page 1 of 2 1 2 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Links monetized by VigLink