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  1. #1
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    Default Shovelhead Shuts Down When Hot

    Looking for some ideas as to what could be happening with my bike now. It's a '73 Super Glide in a hardtail frame, ratchet top trans, Super E carb, kick only. It starts right up in one or two kicks very time when cold, then after about 20 minutes of riding starts to misfire and pop out of the exhaust. It gradually gets worse and worse until the bike just shuts down and will not start again until it has had some time to cool.

    So far I have put a new coil on, new points and condenser, plugs and plug wires, checked and redone timing, checked pushrods, new battery a few months ago, but the problem is still there. I recently switched to the Super E from a CV after the same problem thinking it might have been the culprit, but the bike seems to like the E better when it's running so I kept it. Put new intake O rings on when I changed carbs. The wiring was redone a few months ago when the bike was put together in the hardtailed frame. I've been digging through other threads with similar issues and have found a similar story being solved by replacing the advance unit and weights which I am going to try next. I have not had any engine work done since owning this bike and am unsure of the history behind it. I also haven't changed the regulator. Could the problem be related to the engine itself? Regulator? Battery? Any input or ideas are appreciated.

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    Short

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    Weak battery...........

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    Quote Originally Posted by BuddhahoodVato View Post
    Short
    Ding ding ding. ^^^

    Wire in the harness shorting through the insulation when hot. It happens. I just fixed (I hope) a similar problem. Harness at the handlebar switches ('96 - up style) were pinched where they should not have been. Ran perfectly until fully hot, about a half hour.

    Jim

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    Quote Originally Posted by Tattooo View Post
    Weak battery...........
    A weak battery would fire right up fine then cause these symptoms after riding for a bit?

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    Quote Originally Posted by JBinNC View Post
    Ding ding ding. ^^^

    Wire in the harness shorting through the insulation when hot. It happens. I just fixed (I hope) a similar problem. Harness at the handlebar switches ('96 - up style) were pinched where they should not have been. Ran perfectly until fully hot, about a half hour.

    Jim
    Thanks Jim. I will take a look through the whole harness asap and check for shorts.

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    Another thought related to that – if it were a short, wouldn't this cause the bike to immediately shut off rather than a slow decrease in performance, misfiring and popping over the span of a few minutes ultimately leading to a shut down?

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    Could be a condenser getting ready to let go. Just because they're new doesn't mean they're good, they can break down on the shelf.

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    Quote Originally Posted by HogsRear View Post
    A weak battery would fire right up fine then cause these symptoms after riding for a bit?
    Damn right it will........ Especially on a kick bike with points..................

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    Is your tank vent plugged?

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    Quote Originally Posted by metalheart28 View Post
    Is your tank vent plugged?
    Tank vent seems to be working fine, no difference in performance with gas cap off while running

  12. #12

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    Quote Originally Posted by Tattooo View Post
    Weak battery...........
    I just experienced this. I run a Dynatek S though.... Bike ran great on the highway but once I got into town it would sputter and backfire. Let it sit for 10 minutes and kicked right over again only to start running bad again in a minute or so. Wouldn’t start a third time though.
    Had a bad AGM battery.

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    Quote Originally Posted by Micromark View Post
    Wouldn’t start a third time though. Had a bad AGM battery.
    It's astounding what problems a weak battery will cause......

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    Alright I have ordered a new sealed battery to replace the current lead acid battery I got from NAPA, hoping that it helps. Going to look over the wiring this weekend and see if there are any weak spots or pinched wires. Thanks all!

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    Quote Originally Posted by HogsRear View Post
    Alright I have ordered a new sealed battery to replace the current lead acid battery
    Did you happen to check it to see if it was bad???????????? Or are you just going to assume it's bad??????

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    Quote Originally Posted by Tattooo View Post
    Did you happen to check it to see if it was bad???????????? Or are you just going to assume it's bad??????
    It tested ok not running but I wanted to switch to a sealed battery that fits in the oil bag a little better anyways so I will keep the old one as backup.

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    If your alternator and regulator are operating as intended, don't even need a battery with your points type ignition.

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    Are you still getting a spark on both cylinders after the motor shuts down? Is there fuel in the carb's bowl after the motor shuts down? I have yet to see any results from attempting to diagnose the problem.
    Last edited by Skjoll; 10-10-2019 at 8:56 AM.

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    Quote Originally Posted by Skjoll View Post
    Are you still getting a spark on both cylinders after the motor shuts down? Is there fuel in the carb's bowl after the motor shuts down? I have yet to see any results from attempting to diagnose the problem.
    Yes and yes.

  20. #20

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    What you've described sounds so much like inadequate or zero valve clearance when cold so as the motor heats up and the valve gear tightens up, the valves are prevented from closing completely until they remain open far enough that you no longer have adequate compression for the air/fuel mix to ignite.

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