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Strange SBC problem.

Discussion in 'The Hokey Ass Message Board' started by saeger, Nov 8, 2010.

  1. David Chandler
    Joined: Jan 27, 2007
    Posts: 1,101

    David Chandler
    Member

    My best guesses have all been mentioned, timing, cam, worn distributor parts and timing chain issues. However it sounds as if it's leaning itself out at higher speeds. Perhaps the carb or fuel system is in question? I know an ice cold engine with a broken choke will backfire nicely through the carb, on a frosty morning. Also see if there is any slop in the distributor main shaft. If it's moving around that will cause the points to bounce at higher speeds.
    Good Luck.
     
  2. fearnoevo
    Joined: Nov 28, 2009
    Posts: 218

    fearnoevo
    Member
    from Iowa

    Not sure if you mentioned it. Is it still points ignition?

    If so, I would be cleaning/replacing/adjusting points and replacing the condensor

    I can't tell you how many times I've chased odd running conditions and ended up replacing the condensor and seeing the problem go away.
     
  3. blacktopjeff
    Joined: Oct 13, 2009
    Posts: 17

    blacktopjeff
    BANNED
    from iowa

    I don't know the year of the motor, but I had a 305 from the 70's which had incredibly low compression (factory standard). It was a dog, and the only way to even make it a good dog was to step the timing advance way up. The real solution would be a blower, but I didn't have the money.
     
  4. Look for any carbon tracking or cracks between the terminals inside the distributor cap.....(bad coil/cond/points?) Really hard to diagnose without being there. Can you safely power brake the thing in the dark somewhere and look for cross firing plug wires?
     
  5. Russco
    Joined: Nov 27, 2005
    Posts: 4,194

    Russco
    Member
    from Central IL

    Is the mechanical advance working ? with the vac advance disconnected and timing light hooked up, the timing mark should move at least 2 inches when the rpms are increased to 2500 to 3000. Also mentioned it could be any of the basic stuff plugs, cracked cap, bad rotor wires ETC...
     
  6. saeger
    Joined: Feb 16, 2007
    Posts: 115

    saeger
    Member

    The mechanical and vacuum advance are both working as they should. The cap is new as are the points and condenser. I will try new plugs and a new condenser to see if that makes a difference. Is there anything else to test for or rule out?
     
  7. OldBuzzard
    Joined: Mar 8, 2008
    Posts: 878

    OldBuzzard

    A new cap and an old rotor may not get along too well with each other. New wires??? Leaky wires will crossfire. If the points are too close it will cause a problem. There is not much room for error setting them. Make sure the rubbing block is exactly on the highest point of the distributor cam.
     
  8. saeger
    Joined: Feb 16, 2007
    Posts: 115

    saeger
    Member

    The rotor is also new, I forgot to mention it. The wires are also newish. The dwell was set with a dwell meter. Could it crossfire, but only under load?
     
  9. 1nos487
    Joined: Aug 4, 2010
    Posts: 26

    1nos487
    Member
    from east TN

    lobes where points ride good shape and not worn?
     
  10. drs47ford
    Joined: Sep 5, 2010
    Posts: 108

    drs47ford
    Member
    from Western NY

    I just went through the same thing a couple years ago with a 350 in a 72 Monte Carlo. All the same symptoms....tried all the things you're trying with no improvements. Camshaft was totally wiped out. I'd be really surprised if that isn't your problem.
     
  11. "New" doesn't always mean it's good
     
  12. Can you safely power brake the thing in the dark somewhere and look for cross firing plug wires? (Already posted in #34)
     
  13. saeger
    Joined: Feb 16, 2007
    Posts: 115

    saeger
    Member

    The motor used to run well, then I put in a 262/272 cam, 305 heads, Eddlebrock Performer intake and an Eddlebrock carb. It sounded awesome but didn't make ANY power whatsoever. So I put every thing back stock. I don't think that the stock cam is wiped out, there wasn't any wear on it when I put it in the motor. although I didn't check for valve lift.

    I know the motor was working until I took it apart and now it's not working even with the original parts.
     
  14. Deuces
    Joined: Nov 3, 2009
    Posts: 21,278

    Deuces
    Member
    from Michigan

    Sorry man....... But i have a hard time believing that the timimg is 2 degrees before top dead center... You need to advance it......
     
  15. Deuces
    Joined: Nov 3, 2009
    Posts: 21,278

    Deuces
    Member
    from Michigan

    What other 305 parts did you use on the 307???
     
  16. auto shop
    Joined: Aug 20, 2005
    Posts: 284

    auto shop
    Member
    from kentucky

    Remove the valve cover and watch the rocker move up and down. If it is a lobe the valve will not move up and down as much as the valve that is good. Does it have any valve train noise?
     
  17. saeger
    Joined: Feb 16, 2007
    Posts: 115

    saeger
    Member

    I only used the 305 heads, but now the stock 307 heads are back on the motor. 2 degrees is what it says under the hood, in the Chilton manual, and the factory service manual. I always though it was odd, though, because most other small blocks are timed 4 degrees BDTC.
     
  18. saeger
    Joined: Feb 16, 2007
    Posts: 115

    saeger
    Member

    I did that today, all the rockers appear to move the same amount. There isn't any valve train noise I can hear, well at least not audible over the glass pack.
     
  19. David Totten
    Joined: Nov 21, 2005
    Posts: 248

    David Totten
    Member

    You need to have some one put it on a scope and find out what is wrong and stop guessing.
     
  20. Deuces
    Joined: Nov 3, 2009
    Posts: 21,278

    Deuces
    Member
    from Michigan

  21. saeger
    Joined: Feb 16, 2007
    Posts: 115

    saeger
    Member

    I just went out and power braked it. No cross firing. Dave, I think your right, I have to find someone with an engine analyzer. This might just be the strangest motor problem ever.
     
  22. Deuces
    Joined: Nov 3, 2009
    Posts: 21,278

    Deuces
    Member
    from Michigan

    Did you check the rotor position on # 1 terminal and #1 cylinder on the top of the compression stroke??? Mark the distributor housing under #1 terminal and bring # 1 cylinder up to TDC on the compression stroke and see if the rotor lines up with the mark....
     
  23. jimvette59
    Joined: Apr 28, 2008
    Posts: 888

    jimvette59
    Member

    What distributor is in it. Has any body played with the springs are the weights stuck. Did the dist. gear spin. I would pull the dist. and have it checked.
     
  24. MotionNova
    Joined: Mar 29, 2010
    Posts: 113

    MotionNova
    Member
    from Ohio

    The 350 in my truck started poppin thru the carb under a load one day totaly out of the blue. It had blown the head gasket between two cylinders. The spark would jump across to the other cylinder causeing it to backfire thru the carb.
     
    Last edited: Nov 16, 2010
  25. OldBuzzard
    Joined: Mar 8, 2008
    Posts: 878

    OldBuzzard

    When you adjusted the valves did you snug all the rockers down 'till there was no play? If so, some of them are too tight & when the lifters pump up a little they are holding valves open.
     
  26. OK, back to basics. Do a compression test in all holes.
     
  27. rsluggoboy
    Joined: Nov 1, 2009
    Posts: 104

    rsluggoboy
    Member
    from SALINAS CA

    Had that problem once, Flat cam
     
  28. 1954satan
    Joined: Nov 20, 2009
    Posts: 28

    1954satan
    Member

    hi from the uk, you need to buy a good quality vacuum gauge, correctly read it,ll tell you a whole lot about whats goin on with an engine. thats where i would start from.
     
  29. Rude Dude
    Joined: Dec 14, 2003
    Posts: 356

    Rude Dude
    Member

    Check distributor plate splins on shaft are pressed on ,have been known to break free if it is spot weld under plate. This problem can cause all kinds of havoc and frustration
     
  30. MotionNova
    Joined: Mar 29, 2010
    Posts: 113

    MotionNova
    Member
    from Ohio

    Have you found the problem yet?
    Let us know.
     

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