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Technical Sudden lifter / rocker noise - Potential causes?

Discussion in 'The Hokey Ass Message Board' started by Treozen, Nov 24, 2015.

  1. I always used Autolite plugs in my Drag car. I was convinced to try NGK. First run it sounded like opening day of duck season. Put the old plugs back in,and ran them to rest of the weekend.. Back to the topic.If the adjuster was backing off, the valve would not be operating in time. Which could act like a miss because it was opening late and not far enough.
     
  2. Yuuup
    Drive it into the lake and buy a hotrod
     
  3. Treozen
    Joined: Aug 16, 2015
    Posts: 13

    Treozen

    Well, I also have a 57 chevy and 63 Thunderbird..... my wife wont let me buy anything else....something to do with insufficient room.....whatever that is...
     
  4. wedjim
    Joined: Jan 1, 2014
    Posts: 419

    wedjim
    Member
    from Kissimmee

    It sounds like a weak cylinder may be messing with the vacuum signal causing the carb to run rich. You also have to be careful with a good cam and a carbs power valve. Some PV's open at a point close to idle vacuum in an aggressively cammed engine. Another issue that happens is the idle gets cranked up mechanically at the butterflies so far to get a decent idle speed, causing the carb to be out of the idle circuits. You'll know if this is the case when the idle mix adjustment seems to do little or nothing.

    I have seen spark plugs cause issues, I try to use the same plugs that came in the engine, unless it's had the coil and other mods done ignition wise.
    Bigger problems are usually on newer cars where radio signals are emitted, or feedback into the coils causes odd misfire issues, trouble codes and other anomalies.

    A quick test for a bad exhaust seat(with no leak down tester) is a dollar bill over the tailpipes one at a time at idle. It should never suck the bill toward the pipes outlet. If it does its indicated vacuum signal in the exhaust, which means a leaking exhaust seat during intake stroke.

    Keep us posted.
     
  5. Treozen
    Joined: Aug 16, 2015
    Posts: 13

    Treozen

    So, for the PV, I switched it out to a 4.5, versus the stock 6.5. The cam makes around 11HG at idle but that drops to 6-ish when in gear with a fluctuation over 2-4 HG so The 6.5 may have been opening up when it wasn't needed, though probably not at idle. I doubt the PV is involved, but the 4.5 makes more sense generally anyway. What I did today was throw on a fuel gauge and regulator. At first, the gauge was all over the place with the pulsing from the mechanical pump, but it seemed to hit a high of 8 PSI before going the other way down to 4, and you only want 5 -6.5, maybe 7 max on a Holley SA 770. So I put on the regulator as well, that steadied out the pulses, and sure enough, it read high. I cranked the regulator down until the gunge read around 6. Now I don't know that the PSI was high enough to push past the needles (or whatever Holley uses) but they do insist on proper PSI, so, it certainly didn't hurt. Given that all plugs show at least some sign of carbon foul (though # 3 takes the trophy by far), it seemed to make some sense.

    The 2nd thing I did was take the carb off and set the transfer slots appropriately. I think I was actually close here anyway but it was peace of mind to check. I set initial timing at 16 and calibrated an additional 16 or so from vacuum advance (manifold vacuum). With 20 degrees in the distributor, I would have had 36 total, and 52 at cruise - the magic numbers - but alas, it didn't work. The 16 from the vacuum advance moved the idle up to 1350, which I could adjust down with the idle screw, but that did two things: 1) I lost exact calibration on the transfer slots & 2) When I put the car in gear and the vacuum dropped, so too did the RPM, and bye-bye running motor - with the throttle blades closed up to compensate for 1350 idle and drop it back to 1000, there just wasn't enough to keep running once the vacuum advance dropped out. Instead, I settled for 12 degrees of vacuum advance. I still had to adjust the idle down a bit, so off of the "optimum" transfer slot calibration, but only by a half turn of the idle screw. In this case I'm hitting 28 degrees between vacuum and initial - I wont get to the ideal 50-54 degrees cruise number, but the car stays running.....so...upside, and I can still get 36 total once I curve / limit the distributor. As it stands now, I have the strongest springs on, but it will need limited and calibrated. Even given that though - I had to get gas (used almost a tank so far just dealing with these issues) and it ran better than it ever has -not perfect mind, but better.

    The miss - still there, better I think but far from gone. I will try the dollar bill idea - that's something to keep in the tool belt for sure - nice technique, I had not heard of that one before. I'm more convinced the miss is electrical in nature. Partly because the mechanical causes have mostly been eliminated, and the fuel / air suspects have been switched up and controlled many different ways with no real change in the miss or in some way addressed. I also noticed something tonight that gave me pause. I was out in the driveway, pitch black outside, and I was fighting with the air cleaner (standard 12" Edlebrock) I had a 1 inch plastic spacer between it and the carb, and the threaded rod from the carb was just barely clearing the lid of the air cleaner. What I noticed was a spark....very small blue spark that would occasionally jump from the carb threaded rod, to the air cleaner lid. If you imagine the threaded rod poking through the hole in the air cleaner lid, the spark was jumping from the rod to the inside of the hole, but only when the side of the hole got close enough to the rod. I've no idea why it would jump to the lid, though I suppose it could have been jumping from the lid, but the better question was...where is it coming from? The carb should be grounded, and the lid had no live wires running to it. It would be touching the spark plug wires, but I can't imagine you'd get spark jumping through the wire and across the lid to arc over to the carb...but....maybe? I did the spray-water "starlight " test a while ago to check for spark scatter and didn't see any...but, I saw something odd tonight.

    Anyway - probably more update than you wanted, lol

    Allan.
     
  6. wedjim
    Joined: Jan 1, 2014
    Posts: 419

    wedjim
    Member
    from Kissimmee

    It sounds like your on the right track with the carb settings. As far as the timing goes, I would tune according to what the engine likes best, not a predetermined specification. There are so many variables. I do prefer ported vacuum advance, not manifold vacuum, so it shouldn't effect the idle at all, but still helps at part throttle cruise where you're out of the idle circuits and ported vacuum gets to the advance.
    That should square up your idle and total timing issues.

    The spark is a concern for sure. Sounds like a wire is arching to the air cleaner? Maybe cylinder 3, or the coil? If not...You could try swapping the wire and plug from cylinders 3 and 4, which should be close in length? Then test and see if the miss moved.
    If there is no evidence of arching ignition wires to the air cleaner(I use a grounded test light passed over the wires while the engine is running, looking for the jumping spark), you have something trying to ground thru the air cleaner? Which would be very odd. But in a glass car, I'd go thru engine and chassis grounds first.
     
  7. You need more torque converter.
     
    wedjim likes this.
  8. 327Eric
    Joined: May 9, 2008
    Posts: 2,116

    327Eric
    Member

    X 2 on the grounds. Ground the engine to the frame, and check any other grounds that shoul.d be there
     
  9. Treozen
    Joined: Aug 16, 2015
    Posts: 13

    Treozen

    I plan on trying ported - I admit it goes against the grain - manifold vacuum has been drilled into me for so long, its a bit like deciding I like imports over American Muscle....

    I like the grounded test light idea, I'll try that.

    Its possible, and I'm no torque converter expert, but I am using a step above the acceptable limit for this cam. I think I'd be concerned that if I moved to a higher torque converter to get more vacuum in gear, that I'd create other issues - drive-ability issues maybe, extra transmission heat possibly? I'm not sure what the downsides to more stall are, but my guess is there's no free ride. You get something, but the stall speed taketh something away ;-)

    Yes, I did check all grounds and ran resistance tests - all within spec. Just to be sure, I added an additional large gauge ground from the block to the frame.
     
  10. wedjim
    Joined: Jan 1, 2014
    Posts: 419

    wedjim
    Member
    from Kissimmee

    Torque converters, the squishy connector between the engine and trans. The bigger the cam, the looser and squishier it needs to be.
    A looser one will allow a few more in gear idle rpm, but that isn't it's purpose. Getting the engine up on the cam is. I've also used them to balance traction when tire choices are limited.

    Look elsewhere first, but it is a possibility.

    My wildest street engine build was a 468 big block Chevy. It had a crazy cam, dominator carb and idled at 1050-1100 with no issue, using a 3800 converter. But I used the convertor stall to control traction and 60ft times, not idle speed. :)
     
    loudbang likes this.

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