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Nailhead breaking down at top end

Discussion in 'The Hokey Ass Message Board' started by striper, Aug 22, 2009.

  1. Just so you know I think about the first 1/4 throttle is handled by the idle circuit. the rest is a combination of main curcuit and power valve.
     
  2. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    I'll give your suggestion a go. Can't do any harm and I can always put it back where it was.

    Just wish I knew more about what the motor is actually doing.
     
  3. Pete
    I think you are on the right track. I also think that the balincer really needs replacing before you can get a good handle on where this motor really is.
    PS
    I am 61 years old I did not learn these things overnight. I have Fucked up more shit than you can possibly imagine
    Fuzzy
     
  4. swifty
    Joined: Dec 25, 2005
    Posts: 1,829

    swifty
    Member

    Pete, do you want a lend of the balancer off the 401 I've got here while you send yours to Wagga to get it rebuilt?

    If so let me know and I'll post it to you.

    swifty
     
  5. Are you sure your carbs are sealing to the manifold? I had the same problem once and this was the cause.
    Spray some CRC aroung the carb bases when its running and see if it sounds different. Also try it with the revs up a little.
    Worth a try.
     
  6. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    Thanks heaps Swifty. I'll get back to you on that. I'm not so sure mine has moved. It's embarassing but it only dawned on me a short time ago that I didn't disconnect the vac advance when checking my initial advance. First thing tomorrow :eek:

    Thanks. I'll add it to my list.

    Pete
     
  7. steel rebel
    Joined: Jun 14, 2006
    Posts: 3,604

    steel rebel
    Member Emeritus

    Seem to have worked out the high speed miss on my Cad.engine.

    First I removed and cleaned the emulsion tubes on the four 97s. Ran better.
    Thanks Bruce Lancaster!

    Changed the fuel filter. Ran even better.

    Set the points to a tight .017 and set the timing at about 12 btdc. Runs great. Took it to 6000 rpm without a miss.

    Hope this helped. At least it took you back to the top.

    Gary
     

    Attached Files:

  8. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    Some progress. This morning I checked my advance, this time with the vacuum blocked off. It was bang on 12* BTDC. That is a relief and also says my balancer is OK for now too. Then with the vacuum back on it went to about 24* at idle. As I increased the revs it incrementally climbed but I don't have a measurement of total advance. I would estimate it could be somewhere around 40*.

    Then I screwed in the mixture screws on my outer carbs 1/2 a turn. All 3 are now 1 turn out. Brought up the revs and it ran nice. No pops or misses.

    So I took it for a short drive, gave it a squirt and all good again. So I decided to have a real test drive...my first one really...about 5 miles.

    It went pretty well but I still felt it stop pulling a bit at maybe 3500 - 4000 (still guessing). I have a lot of exhaust noise due to only having baffled headers at this stage but it didn't seem to be popping as much.

    In the final stretch up my road I gave it a little and the popping came back. Back in the shed it ran up OK again. I think I've made progress but I'm not there yet.

    Checked the plugs. All the right bank were a nice light brown. On the left #8 was rich, #6 and #4 looked a little light and #2 was good.

    I'll keep fiddling

    Pete
     
  9. DRUGASM
    Joined: Dec 16, 2008
    Posts: 2,772

    DRUGASM
    Member

    the nailheads are NOT really meant to make high rpm power....the stats i saw in the chiltons manual on my 401 showed max torque was like 2800rpm. thats pretty low compared to alot of other engines.

    good luck sorting out the problem though,...these kinda problems are always hard to troubleshoot.

    drew.
     
    Last edited: Aug 25, 2009
  10. sdluck
    Joined: Sep 19, 2006
    Posts: 2,751

    sdluck
    Member

    What size fuel line and what kind of fuel pressure are you running.
     
  11. sdluck
    Joined: Sep 19, 2006
    Posts: 2,751

    sdluck
    Member

    Rev it up and see if the timing jumps around could also be points floating,are the good points?
     
  12. Pete
    Try to figure out what your total timing is. By this I mean while you have the timing light hooked up slowly rev the motor and watch how far out the timing goes. should be around 36 degrees.
    Another thing you may try
    Disconnect the vacuum advance, block off the hose, set the timing around 18 degrees and see how it does.
    From what you have described your timing is using manifold vacuum which is advanced at idle or when you have a lot of vacuum but retards as you lose the vacuum IE: Accelerate.
    What all this means is that as you accelerate the timing is advanced by the weights but is being retarded by the vaccum advance so that it is firing too late to burn all the fuel in the cylinder. The bore on this motor is 4.185 so it takes a lot of timing to get the fuel burned. Fuel burns at a constant rate so that being said as the motor sppeds up you need to advance the timing to get the fuel burned sooner. In a perfect world all fuel should be burned as the piston just passes TDC. So all power is placed on the downward power stroke of the piston.
    Keep your chin up we will get it!!
     
    Last edited: Aug 25, 2009
  13. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    Running 3/8 steel lines and around 6psi. I want to run lower but the damn reg won't play ball.

    No it's pretty steady

    Sure, I can try that, why not? Oh I know why not. My fuel pump just decided to take a dump. But once I get a new one I'll try it. BTW, yes I am using manifold vacuum.
     
  14. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    tommy
    Member Emeritus

    My motors manual calls for 2 1/2 deg BTDC on the 66 401/425 with the vac adv. plugged (initial advance) unless you have the dual quad 425 HP engine. And if you suspect that the ring on the balancer has moved, you can throw away your timing light. It's useless with that balancer.
     
    Last edited: Aug 25, 2009
  15. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    My manual says 5 deg BTDC for a synchro shift and 12 deg BTDC for an auto. That said I should be setting it to 5 deg but it runs better at 12 so I figure, why not. It's a '61 401.
     
  16. CC72
    Joined: Aug 27, 2009
    Posts: 4

    CC72
    Member

    newb here, sounds like your on the right track. Someone mentioned valve float,-valve springs, this has haunted me before. The car would rev like mad til I gained traction then it didn't matter what I did would not go over 3500-4000 rpm.
     
  17. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    I hope this is not it. Much harder to play with that carb and timing settings.

    I'm out of action for now. My fuel pump started pissing fuel out the last time I parked it so it's somewhere between Australia and Nebraska (Speedway) right now, along with my not working fuel reg. I'm taking the opportunity to re-invent my throttle linkage for the 3rd time.

    Pete
     
  18. Pete
    Any updates???
     
  19. oldtime
    Joined: Oct 18, 2008
    Posts: 27

    oldtime
    Member

    Check and make sure you're getting full throttle. That will make for some of the symptoms you're describing. Don't ask how I know this.

    Old Time
     
  20. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    It's not a throttle issue. I know for a fact i wasn't getting full throttle which is why I'm reinventing my linkage. It's more like misfiring, maybe valve bouncing.

    No updates Fuzzy. I'm out of action until I get a new fuel pump
     
  21. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    Thought I'd bring this old one back up now that I've had a chance to drive the car a bit. I now have a better idea what is happening.

    I suspect I'll need to put it on a dyno but since I've had the car out for a couple of long runs now I can say that the car runs good on the centre carb. As soon as I see the secondary linkage start to move it's like someone pulled 2 plug wires off.

    I'm not smart enough to know what is happening but at least I now know when.

    I'm not expecting a solution but some opinions would be good. Too much fuel? too little fuel? Dodgy power valves? Loss of vacuum advance due to opening secondaries?

    I'm just throwing it all out there.

    Pete
     
  22. After seeing your car at chopped, I would look at the angle of your carbs, your motor is parrallel and your carbs are angled 'down' therefore I think the floats are giving you not enough fuel to keep up.....I think changeing the height of your floats may fix your problems.............does that make sense???
     
  23. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    Makes sense. It's strange though that it doesn't seem to affect the centre carb. Runs good until the secondaries start to open.

    It was a bit of a compromise setting up the engine. The main issue is those Offy intakes have a really steep angle on them so if you want the carbs level the engine has to lean back a long way. Couldn't do that in my car.
     
  24. striper
    Joined: Mar 22, 2005
    Posts: 4,498

    striper
    Member

    Closest thing to a profile shot I have to illustrate Human Fly's point

    [​IMG]
     
  25. Shifty Shifterton
    Joined: Oct 1, 2006
    Posts: 4,964

    Shifty Shifterton
    Member

    Based on the new info.....If that was my car I'd be taking the end carbs apart to find out where the fuel restriction is. If you have a clogged jet/passage/main circuit that's not flowing enough fuel it'll do exactly that. Pretty common problem in the world of multi-carb motorcycle/ATV that sit for 6 months of the year.

    You may be able to unhook one carburetor from the linkage, and try to isolate which carb is to blame. Without flowing fuel, those carbs are just huge vacuum leaks.

    Sometimes debris flops around, causing the amount of blockage to vary. It'll drive ya nuts because you can mess with other things, testdrive, and see it run better or worse as the debris moves around.

    good luck!
     

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