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  • #1

    Misfire

    I have discovered some of you guys are good at diagnosing ignition and carb problems.
    My XS11 runs real sweet with one small problem. Under load accelerating in first there is a slight misfire. The harder I accelerate the bigger the miss.
    Most of the time the miss is not there, just when nailing a Harley.
    My suspicion is a bit of blockage in the small jets. I have not checked anything on this engine but plan on swapping the plug caps next week.

    Just got the 400 Seca on the road. At WOT above 7000 going for 8000, there is a steady miss that may not be in sync to the revs. My guess on this is bad plugs or a coil breaking down.
    I have cleaned the carbs on this bike but not checked the diaphragm things.

    Normally I would have checked everything but have been busy with many other chores. And it is easier to type a message to you guys on a rainy day.

    Both bikes are quite serviceable the way they are. But I need more speed from the 400 in case I meet old British on the road.

    Unkle Crusty
    Tags: None
  • #2
    Originally posted by Crusty Snippets View Post
    I have discovered some of you guys are good at diagnosing ignition and carb problems.
    My XS11 runs real sweet with one small problem. Under load accelerating in first there is a slight misfire. The harder I accelerate the bigger the miss.
    Most of the time the miss is not there, just when nailing a Harley.
    My suspicion is a bit of blockage in the small jets. I have not checked anything on this engine but plan on swapping the plug caps next week.
    I guess I cant comment on the Seca. Missing on hard acceleration probably has nothing to do with caps or plugs. I suppose it is possible that spark is weak, but if the engine is running fine at constant speeds within that range, it is probably a carb issue or a pick-up coil issue. One jet that is very easy to foul is the main air jet...it is the pressed-in jet. If those get plugged, I would expect the mixture to be rich. If I remember TC's video, the slides raise quickly on acceleration and then settle down.
    Skids (Sid Hansen)

    Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

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    • #3
      Originally posted by Crusty Snippets View Post
      I have discovered some of you guys are good at diagnosing ignition and carb problems.
      My XS11 runs real sweet with one small problem. Under load accelerating in first there is a slight misfire. The harder I accelerate the bigger the miss.
      Most of the time the miss is not there, just when nailing a Harley.
      My suspicion is a bit of blockage in the small jets. I have not checked anything on this engine but plan on swapping the plug caps next week.

      Just got the 400 Seca on the road. At WOT above 7000 going for 8000, there is a steady miss that may not be in sync to the revs. My guess on this is bad plugs or a coil breaking down.
      I have cleaned the carbs on this bike but not checked the diaphragm things.

      Normally I would have checked everything but have been busy with many other chores. And it is easier to type a message to you guys on a rainy day.

      Both bikes are quite serviceable the way they are. But I need more speed from the 400 in case I meet old British on the road.

      Unkle Crusty
      Pull the left side ignition cover, and using two hands, pull those pick-up coil wires to see if one has broken wires inside the insulation.
      81H Venturer1100 "The Bentley" (on steroids) 97 Yamaha YZ250(age reducer) 92 Honda ST1100 "Twisty"(touring rocket) Age is relative to the number of seconds counted 'airing' out an 85ft. table-top.

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      • #4
        Hey Crusty,

        Are you sure it's a MISS? Some folks have described a "miss" under hard accel in the lower gears and then learned they actually had the 2nd gear skip going on....can also occur in 1st. And it shows up more the harder you twist the throttle in the lower gears. Try shifting into 2nd sooner and then get on the throttle and see if you experience the miss. If not, then it's probably not the ignition/carbs, but may be tranny?

        For the 400, like you said, could be coil going weak, could also be running low on fuel in the carbs since you're running at hi rpm for a while??

        T.C.
        T. C. Gresham
        81SH "Godzilla" . . .1179cc super-rat.
        79SF "The Teacher" . . .basket case!
        History shows again and again,
        How nature points out the folly of men!

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        • #5
          +1 for the pick-up coil wire problem. I've had to fix this a couple times on mine. Your issues sound exactly like what I was experiencing.

          Good luck!
          '80 SG with motor from a '82 XJ

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          • #6
            Misfire

            Thanks for the suggestions so far guys.
            I checked the wyres on the XS11. Everything looks new in there. I will have to spend more time inspecting later.
            Will look at the plugs when installing the new caps.
            There is another misfire that happens in the rain. That's the reason for the new plug caps.

            On the Seca 400 I pulled the plugs. This unit is running lean. It runs fine but may not be getting enough fuel for high revs at WOT. Next check will be the diaphragm things as they are easy to get to.

            In between bike work I have to split my tractor and look for starter motor pieces at the bottom of the ring gear.

            Unkle Crusty

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            • #7
              More info

              Yami the XS11 is running too rich. It may be loading up on heavy acceleration. Gas mileage is crappy. New plug caps installed. 70 miles to ride on Friday.

              The Seca runs quite well to 6000 revs. From there WOT causes a misfire, backing off the throttle allows him to go to 7000 revs and beyond.
              In neutral and no load, he buzzes to 9500 easy. I pulled the carbs to get the jet numbers. Will change to larger main jets when I get them.

              Unkle Crusty

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