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Thread: M35 Linkert Problem

  1. #1
    Join Date
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    Default M35 Linkert Problem

    I had my '47 FL judged awhile back knowing that it had an incorrect carburetor (M74B) and it did quite well. I'd now like to elevate its status past Junior 1st. So in the interest of correctness I found the correct M35 body, built up the carburetor and installed it on the bike. All needles, seats, float (Cotton), throttle shaft bushings, Peek manifold seals, gaskets, etc. were replaced. The float height is set to 1/4". Initial settings are 5 and 2 turns out which should be a little rich. The carb bore is smooth without any signs of gouging or eccentricity at the throttle disk area.

    The bike always was and remains a 1-kick starter when cold. However, when it warms up, it intermittently kicks back through the carb at a medium idle with the choke at 1 click and kicks/stalls at normal idle speed indicating a lean condition. I bubble-tested the manifold as per Cotton and it's leak-free. The gas tank is half-full and the gas flows freely through the line when disconnected from the carb. Also, after re-installing the M74B, the motor runs correctly.

    I'm no new-comer to rebuilding Linkert carburetors. However, I don't have much experience with M35's and this one has me a bit stumped. I'm thinking that it may be a defect in the brass casting as I've taken it apart twice, carefully examined the low speed circuit, but can't find the problem.

    Any suggestions?

    Thanks,
    Bill Pedalino
    Last edited by Bill Pedalino; 06-09-2019 at 09:40 AM.
    Bill Pedalino
    Huntington, New York
    AMCA 6755

  2. #2
    Join Date
    Jun 2001
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    Central Illinois, USA
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    Default

    Sorry but I must ask, Bill,..

    You didn't use a tire or air mattress pump for the bubble-test, right?

    Did you grind the carb and manifold flanges flat?

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  3. #3
    Join Date
    Jun 2010
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    294

    Default

    Initial settings are 5 and 2 turns out which should be a little rich.
    A little rich ? Yes, no kidding, like politics are a little crazy.
    Start at low speed=3.5 turns, high speed=1.125
    M35 needles differ from M74 needles.

  4. #4
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    Mar 2005
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    Huntington, New York - American Zone
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    Default

    Quote Originally Posted by T. Cotten View Post
    Sorry but I must ask, Bill,..

    You didn't use a tire or air mattress pump for the bubble-test, right?

    Did you grind the carb and manifold flanges flat?

    Cotton,
    Thank you for responding.


    ....Cotten
    Cotten,
    Yes, I always draw both flange across 400 grit paper placed on a thick glass plate until smooth. I use my shop compressor with a small inline regulator set to 14 psi. To test the regulator's capacity I briefly pump it up to a point where it strongly pushes past the intake valves and it holds at the set pressure. I then back it off to 14 psi and bubble test with Snoop. This is the setup that you suggested years ago and I use on all my carb tests and it works quite well.
    Bill Pedalino
    Huntington, New York
    AMCA 6755

  5. #5
    Join Date
    Jun 2001
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    Central Illinois, USA
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    Default

    That would seem to incriminate the M35, Bill,

    (But if its an original brass '47 manifold, I would pull it and bench test at a full 15psi anyway.
    They are pretty cheesy sometimes, where you might not be able to see it.)

    I'm not psychic, so I would have to be able to smell it in my own hands for any guesses.
    My philosophy is that tiny things add up, and only being fanatical has kept me in business.
    So even if the bore is pristine, there still shouldn't be daylight around the disc when fully closed, or around the venturi of course.

    I agree with 1950Panhead's suggested needle settings, so air has got to be coming from somewhere.
    An un-lit propane torch might give clues while its idling, if you can get it focused at the ends of the throttleshaft, manifold flange, gallery plugs, etc.

    .....Cotten
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    Last edited by T. Cotten; 06-13-2019 at 07:15 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  6. #6
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    Default

    Cotton,

    I agree that the M35 is the culprit, as the M74B works fine with the settings around 3.5 and 1.5. I don't believe that the needle settings are the problem, as the problem reflects a lean condition. The manifold is an aftermarket but it's been tested on the machine several times at 14 (+) psi with both carburetors.

    I have a friend (Rich Brown - H.D. Generator Service) who is sending me an assembled M35 which runs fine on his '46 EL, so I can confirm that it is the carb, although at this point I'm certain that it is. If the replacement carburetor runs well I'll probably disassemble my carb one more time, triple check the needles, disk-fit, throttle bushings, venture fit, and the machined slot (I still have no idea how Linkert machined that slot). If I can't find the problem, I'm going to look for another M35 body.

    I purchased the correct, shorter low speed needle (27340-33) when I did the original assembly. However, I'm now second-guessing whether or not I received the correct one. The long and short needle tapers look identical, with the length appearing to be the only difference. I have to check, but I'm not certain that the later needle would work in the M35 body's choke assembly, but you would probably know that offhand.

    Finally, I do have to check the main nozzle, although I suspect that is shouldn't affect the idle circuit. I believe that I should have P/N 27332-50, but I need to look at it and confirm.
    Bill Pedalino
    Huntington, New York
    AMCA 6755

  7. #7
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    Uh oh, Bill!

    The -33 LS needle is for 1" Models.

    At least we found the cause.

    Glad it was something simple...

    ....Cotten
    Last edited by T. Cotten; 06-14-2019 at 10:08 AM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  8. #8
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    Default

    Cotton,
    I removed the low speed needle from the knob and it's length is 3.520". Therefore, it looks like it's the correct P/N 27336-27 and not as I previously stated.
    I really thought we had an Ah-Hah moment !
    Bill Pedalino
    Huntington, New York
    AMCA 6755

  9. #9
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    Poop.

    (Can I say that?)

    Times like this, Bill, I take everything back apart, and put it all back together,
    and hope the gremlin jumps out.

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  10. #10
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    Default

    Amen to that brother. You're correct and that's my plan exactly. Because I work away all week, I'm going to put the bike aside for a week or two until I can take a full day to remove the carb, disassemble it and really focus. I must have screwed something up - maybe a wrong part, incorrect or leaky venturi or main nozzle, maybe I honed the throttle bushings a little too much - who knows...
    But a complete, systematic (and calm) re-do should hopefully ferret out the gremlin.

    I'll report back after completing the Phase II rebuild.
    Bill Pedalino
    Huntington, New York
    AMCA 6755

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