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1977 XS360 Refuses to stop misfiring on right cylinder - While riding it

Discussion in 'The Garage' started by got20z, Aug 11, 2019 at 7:05 PM.

  1. got20z

    got20z 1977 XS360

    Hi guys,

    My dilemma is that my '77 360 runs awful and misfires awful while under load/riding on the right cylinder. I just finished the bike as a custom project and I'm running out of ideas. Here is my setup and what I've done so maybe somebody can help me.

    Stock carbs, stock jetting, stock air filters, stock headers with aftermarket mufflers but they are the same size as stock. Bike has 7500 miles

    What I've done or checked:
    Swapped the condenser twice
    Points - replaced and checked several times.
    Valves - Adjusted minor to get back in spec.
    Spark plugs, wires, caps. Spark is good at the plug.
    New carburetor boots.
    Checked carb sync with my harbor freight gauges.
    Set floats to spec. (one was leaking when I first put them back together)
    Adjusted carb pilot screws several times trying to find a balance because the plug on the right cylinder was pretty black like it was running rich.

    When I put the bike together I had trouble getting the right cylinder to fire at all but FINALLY figured out that the valves needed adjusted on that side and the points were out of spec. I replaced the points today because I couldn't help but think it was something to do with ignition causing my problem. It didn't really improve after doing that and test riding it.

    The bike idles decent. It misfires on the right on idle as well but nothing like when riding. I would say 15% + throttle and the misfiring starts, it bogs with WOT and doesn't want to pull that hard. With barely any throttle or slowing down it feels pretty good and the misfiring stops. I had it up to 50mph but had to lean on it pretty hard to get there. I've had the carbs apart 3 times to re-clean them and I know they are clean even though the first time is never enough.

    I feel like now it's maybe the slide needles needing adjusted in the carbs but I have a mostly stock setup so I haven't "gone there" yet.

    Any help appreciated. Sorry for the long post!
    Last edited: Aug 11, 2019 at 7:22 PM
  2. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Have you checked the timing on the right side point?

    When I adjust points, I set the left side first... This is a MUST DO step. Then you will be able to set the right side. The right side points plate can be moved to advance or retard the timing INDEPENDENTLY. This has nothing to do with point gap.

    The right side point is completely independent from the left side point and the right can be adjusted by itself AFTER the left side is set. Advancing/retarding the left side will move the whole point assembly and change timing on both sides.

    You need an induction light to get the left side as best as you can, Then you simply match the right side so both cylinders fire with the same amount of advance.

    I hope that clarifies things for you even though you said you messed with the points. If its not timing, break out the voltmeter and start testing ignition components.
  3. got20z

    got20z 1977 XS360

    Thanks for the reply Mike. I'm planning on checking the timing next chance I get since I've exhausted pretty much all other options. I also forgot to mention I put a coil on from another 360 that runs fine and I have the same problem so it doesn't seem like the coil for that cylinder is the issue. I'm hoping it's the timing causing it so I know I'm getting close to working it out.

    Thanks again.
  4. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Yea first thing to do is check both sides with an induction light, I bet the right side is firing too late, this will produce a terrible idle and will run slightly better when throttled up.

    After you make your adjustments, make sure that both sides fully advance to the advance lines on the flywheel marks. They should be VERY close but may not be absolutely exact.

    When installing new points, I like to check the gaps frequently for the first week or two of riding. There will be some wear initially that will change the gap before they "settle"
    buztabuzt likes this.

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