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Thread: Difficulty starting a rebuilt 48 Panhead FL

  1. #1

    Default Difficulty starting a rebuilt 48 Panhead FL

    Hi Guys

    Prior to chroming and painting this 48 needs to run perfectly and I'm having problems starting her. She splutters for a few seconds but doesn't catch on.

    I've never had the bike running and this is my first Harley so I need to check a few things;

    Timing is spot on, it has the later auto advance unit, points gap is correct.
    Spark Plugs are new Champion J12YC, gap correct, sparks ok
    Timing gear marks all line up
    It has solid pushrods, adjusted properly
    Inlet manifold has been removed cleaned and new brass packing bushings fitted, greased - not pressure tested
    Inlet nipple holes sealed - not pressure tested
    Heads removed, valve seats look very good, but not lapped in by me.
    Heads are from 1950, not 48.

    I have two concerns - compression is only 60 psi on front and back cylinders, after about ten kicks, with oil in cylinders - this seems low?
    The carb is an M-74, not the original, this has been cleaned, and set up as per the service manual, float level checked, needles set up per manual, no leaks - is the larger carb a problem?

    Unless advised otherwise, My next steps will be to lap in the valves to increase compression and pressure test the inlet manifold - any other ideas?

    Thanks for your support

    Greg
    Last edited by harleygreg; 04-06-2019 at 09:13 AM.

  2. #2
    Join Date
    Jun 2001
    Location
    Central Illinois, USA
    Posts
    4,078

    Default

    Quote Originally Posted by harleygreg View Post
    ...Inlet manifold has been removed cleaned and new brass packing bushings fitted, greased - not pressure tested
    Inlet nipple holes sealed - not pressure tested.... Greg
    What are you waiting for, Greg?

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

  3. #3
    Join Date
    Oct 2011
    Posts
    452

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    You can check float level,but it is correct fuel level your looking for.I like to watch the bowl fill with it off the carb,but connected to fuel line while plugging the stem hole.Level,fill rate are easily verified.
    Try richining g up the idle and hs alittle.
    Tom

  4. #4
    Join Date
    Jul 2010
    Location
    Ohio
    Posts
    650

    Default

    Are you advancing the cam when you check timing?
    Bob Rice #6738

  5. #5
    Join Date
    Mar 2017
    Posts
    283

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    I also had that problem with compression in my front cylinder. I readjusted the valves and compression came up. I agree with the post above mine on timing an advanced distributor as I did it wrong early on.
    Good luck!

    https://m.youtube.com/watch?v=zFti-dUkSaU&t=24s
    Last edited by ryan; 04-06-2019 at 11:11 AM.

  6. #6
    Join Date
    Jun 2001
    Location
    Central Illinois, USA
    Posts
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    When you are tired of chasing your tail, Greg,..

    Please note when you bubble-test that the '48-early '49 silver-soldered steel manifolds are quite malleable.
    All manifolds should have the flange ground flat, and the malleable ones occasionally need massaging first.

    Note also, inside the bore of the attachment, the dot of silver paint sealer upon a dimple mark.
    When the manifolds were assembled for sweating, a pronged staking device secured the flange to the rest.
    These dimples occasionally leak.

    The spigots are typically crushed from use, so please make certain your new seals are a very sweet fit.
    The looser or out of round, the more likely you will destroy an inlet nipple rivet attempting to tighten them to stop bubbles.

    ...Cotten
    PS: Valve seats shouldn't need lapping, if properly cut with modern equipment.
    Lapping widens the seat, and embeds carbide into the bronze.
    Attached Images Attached Images
    Last edited by T. Cotten; 04-06-2019 at 11:49 AM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  7. #7

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    In my experience, coughing without starting means it needs more gas, could certainly be a vacuum leak, but I don't like the low compression. You should have over 100 with oil on the rings. Low pressure means reduced vacuum in the manifold even if properly sealed. 1 tooth off on the cam (42 teeth) is really big - 17 degrees, it may be retarded, even 2 teeth, although I suspect your exhaust valve may hit the dome during overlap.
    You can fake a milder/less retarded cam by simply making the intake valve lash really loose - but don't run it that way. If the CCP comes up immediately I suspect the cam.

  8. #8

    Default

    Thanks Guys, this is good input on all aspects, I shall check all these and respond in a couple of weeks,

    Greg

  9. #9

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    Hi Tom, interesting comment about fuel level, as I've checked this using your method, and set the float height (brass) as advised in the service manual/Palmer to 5/16" from the rim. However, it would be good to know what the fuel level should be, as this would be the relevant measurement?
    Thanks
    Greg

  10. #10
    Join Date
    Jul 2006
    Location
    Central Florida
    Posts
    928

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    Ditch the brass float. They are heavier than stock and totally unreliable.
    It's been my experience that sooner or later, every one leaks fuel, and sinks. Every. You are not the first to pull hair out trying to trouble shoot a brass float. The black plastic ones, either molded, like Rubber Ducky, or turned on a lathe, like Liberty or Mark Neberman's Chicken Plucker, never, ever sink or give trouble. White molded ones have a tendency to swell up after time (they all live in a gasoline bath, 24/7) and hang up on the interior of the bowl. Don't feel like The Lone Ranger; brass floats suck. Literally, suck up gasoline and sink.

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