Question about 2002 Harley Davidson FLHR - FLHRCI Road king

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Misfirering one piston Change plug ,plugwires,

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You didn't say whether the cylinder was misfiring occasionly or not firing at all. The number of things that could cause that are quite high. From an ignition standpoint, you could have a bad coil or a bad ignition unit. From a mechanical standpoint, your compression could be low. From a fuel standpoint, you didn't say whether your engine was fuel injected or carb equipped, you might not be getting fuel to the cylinder or you might have a vacuum leak at the intake.

Check the spark first. Pull the spark plug wires off but leave the spark plugs in the heads. Install another set of plugs in the wires and lay them on the engine where you can see them. Spin the engine with the starter and watch for spark. If you have spark, is it a bright blue spark or is it a yellow looking spark? The bright blue spark is what you want.

If you have good spark, run a compression test on the engine. Screw a compression tester into the spark plug hole and open the throttle wide open. Spin the engine to test for maximum compression. Write down the reading you get. The squirt about an ounce of oil into each cylinder and run the test again. If the compression comes up more than 10%, it may be time for a top end overhaul.

Try this and repost with information and we'll go from there.

Good Luck

Posted on Nov 14, 2010

  • mictinner Nov 17, 2010

    runs strong under throtle sputers under nutral throtle

  • wd4ity
    wd4ity Nov 17, 2010

    It sounds like you're running too lean in the mid-range of your carb or fuel injection. You may have a vacuum leak causing this. If this is something that has just started, I'd suspect a vacuum leak somewhere. Intake manifold to heads or carb seal on the intake. There's also a vacuum hose that goes to the VOES and the fuel petcock. Make sure this hose has not come loose and has no cracks in it.

    If your engine is equipped with a carburetor, you can change the slow jet. The bike should have come with a #45 slow jet. You can go up to either a #48 or a #50. You'll have to drill the "anti-tamper" plug out of the carb so you gain access to the idle mixture screw beneath it. Screw it in until it bottoms out lightly and the come out about 3 1/2 turns. When the engne warms up, adjust this screw to obtain the highest smoothest idle. You may want to remove the needle from the slide and add a 3mm flat washer under the boss on the neede. The washer should be between 0.020" and 0.025" thick. Put the washer on the needle from the long side so that it raises the needle the thickness of the washer and richens the mid-range operation of the carb just a bit.

    If the bike is fuel injected, you'll have to take it to a dealership or an independent shop that can adjust the fuel map of the injection system.

    I hope this helps.

    Good Luck



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