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  1. #1

    Default Ugh. My new Shovelhead not firing on rear cylinder?

    I just picked this 79 Shovelhead up 2 days ago. Owner said carb needed to be cleaned (mikuni). Got it home and started it with starter fluid (bad mistake). The next day I actually cleaned the carbs and put fresh gas in it. I rode it for about 30 mins straight with no issues. Parked it for the night. I tried to ride it to work and got half way there (15 mins) and it started to misfire. Sounded like it was bogging down, so me, thinking it was the carb and tank and hoping it wasn’t missing, took it home. I cleaned the carb, tank and got new plugs. Started it up, and it sounded the same. I felt the exhausts and the exhaust to the front cylinder was hot, the rear was not.

    This bike Is not stock
    93 ci
    Big bore jugs
    SS piston rings
    Duel plug SS heads
    Single fire ignition
    Andrews cam
    Solid lifters
    Roller rockers


    Things I’ve done so far
    Cleaned carb and tank
    Put known working front plug wires on rear and rear plug wires on front. Same deal. Front cylinder exhaust hot, rear is not.

    Any suggestions?

    Edit: Forgot to mention that as it was bogging on the way to work, it was intermittently run fine again for at most 2 seconds. It this a few times before never running on both cylinders since then. The carb also pops a bit as well.
    Last edited by Superman27e; 04-03-2020 at 5:38 PM.

  2. #2

    Join Date
    Sep 2014
    Posts
    1,458

    Default

    Sounds electrical. is it points or electronic ignition ? Kickstarter still on it. Just asking before giving you some general troubleshooting .
    Last edited by 47str8leg; 04-03-2020 at 6:05 PM.

  3. #3

    Join Date
    Dec 2018
    Posts
    1,682

    Default

    Your symptoms are of an ignition module going bad.
    But, one thought: when replacing the plugs, are you replacing all four?

    Jim

  4. #4

    Default

    Quote Originally Posted by JBinNC View Post
    Your symptoms are of an ignition module going bad.
    But, one thought: when replacing the plugs, are you replacing all four?

    Jim
    Yep. I replaced all four.

  5. #5

    Default

    I just found out that one of the coils has no fire on both coil wires, but the other coil has fire on both coil wires.

  6. #6

    Join Date
    Dec 2018
    Posts
    1,682

    Default

    Quote Originally Posted by Superman27e View Post
    I just found out that one of the coils has no fire on both coil wires, but the other coil has fire on both coil wires.
    Does each coil serve one cylinder, or is it set up as a wasted spark system with wires from each coil going to each cylinder?

    Jim

  7. #7

    Join Date
    Dec 2018
    Posts
    1,682

    Default

    Good first step would be a compression test (throttle fully open).

    Jim

  8. #8

    Default

    Electronic ignition and yes, Kickstarter still on it.

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