Evo Cylinder Misfire

Question Need Help. My 1988 Springer Softail has had a problem over the last 5 years or so, always the same thing. It runs like its only hitting on one Evo cylinder sometimes, but all of a sudden it will start running fine. I have had it in the shop a couple times only to have them work on carb but problem still happens. I even put a new S/S on it to see if that helped but ran good for a while and then back to same thing. One day it might run fine but I will get few miles down the road and it starts spitting and coffin and running shitty but all of a sudden it clears right up. I just put a new battery, changed fuel, changed all fuel lines and it starts right up now and sounds good but when you take it for a ride it kinda feels like a plug is fouled. That is my next step to change plugs. Any ideas? I don’t chance even ridding it for the last few years?

Answer If something seems to be running on 1 cylinder, you usually look into the ignition, or something electrical. Determine what you have for an ignition coil. Test the coil for ohms resistance. You can usually find the specs (for most coils) on line, or in forums. Check your plug wires. Make sure they are not corroded or cut. Make sure they are secure. Determine what you have for an ignition (pick up). Visually inspect it. See if you can find a test procedure for it. Test your charging system. Trace your ignition wires. Make sure that they are all secure and that none are creating a dead short. Inspect your ignition switch and breakers. Make nothing is touching ground in those areas.

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23 Responses to “Evo Cylinder Misfire”
  1. Tom Allen
    Tom Allen

    I had a similar situation with my 1989 Electra Glide. I had put a rebuilt CV carb on it, and I had thought that maybe it was that or the jets. That wasn’t it, nor did the new air filter help. The coil was Ok too. Then a new Ultima programmable digital ignition system was put on. It’s running like a top now. There was a short in the ignition.

  2. Vale

    hi, great support!!! in my opinion ( sorry for intervention) plug wires can come out while ridding due to vibrations, one of my friends had this problem before – thx and safe ride!

  3. john raymond
    john raymond

    old iron heads were famous for this problem,usually the guilty cylinders push rods got out of adjustment and didnt open the valves enough to run that jug,some times its the simple things a computer cant read.

  4. gordon

    Check ur ignition coil. And also check plug wires at the coil end… many will corrode or straight wear out inside the boot. One other thing to check is ur ignition… if it is a dual fire it is possible that it is going bad and intermittently dropping one cylinder.

    • Edwin

      Check/change your plugs…sometimes a bad or cracked plug can cause an intermittent misfire.

    • Bruce Donovan
      Bruce Donovan

      Have 87 1100 evo and runs ruff like miss fire, higher rpms sounds good but 2 to 3 thousand rpm Sounds like misfire. Need direction to go to eliminate problem? Have changed plugs and fuel additive in case of bad gas

  5. Bogies299

    2010 limited seems to run on one cylinder at times. Also, after idling for a few minutes the rpms rise and fall from 1000 to 1500 and even dies. When I try to start it when it’s hot, I have to actually twist the throttle to get it to fire. Thanks for any help!

  6. Don

    For the EVO issue I would also check to see if the choke is sticking and making it rich which would foul the plugs. They would clear up when running higher revs then foul again when revs lower. The fouling one would look sooty.

  7. Mickey Rudolph
    Mickey Rudolph

    I had the exact same problem last year with my 1988 Heritage. Did about everything you have mentioned with no help. Finally figured out it was the cut off switch. Changed that and bike has been running great ever since. Good luck

  8. Jazz Black
    Jazz Black

    One carb feeds two cylinders. One cylinder not firing will NEVER be the carburetors problem.
    For combustion, air, fuel and ignition or ignitor/ fire-spark. Air and fuel are delivered simultaneously from one source, equally to both cylinders. Spark is individually sent to each cylinder in a timed manner. The problem is in the ignition system.

  9. Babzilla

    Always simply check your battery connections at both ends of the wires. Make sure the cable ends are clean of any corrosion and “tight as a fish’s arse!”

  10. norman

    mine was just a fuel filter that couldnt keep up with the flow it ran good for a few miles then spit sputered then came back to life couldnt figure it out for a while

  11. Marvin Richardson
    Marvin Richardson

    My 86 FXR had similar problem finally discovered intake gasket in head had disfigured causing it to suck air.

  12. Steve

    I have a 1990 FLHTC. It would run on one cylinder and then seem ok. checked the intake manifold for leaks, discovered the studs were pulled out of the bottom end. Fixed the studs with Time serts , works now.

  13. Bob Coy
    Bob Coy

    Different question sorry. I’ve a 2004 Softail FXSTI I just replaced my speed sensor but my speedometer is still moving til it max’s out. Please do you have any thought on this I tried to bring up a code all I got was dIA9 I think. that’s what showed

  14. Bruce Marple
    Bruce Marple

    I had the same problem with my 82 FXR. I had it in the shop several times and they couldn’t find anything wrong. It turned out to be a coil wire that was hanging down on one of the cylinder fins. It had burnt/rubbed through and was shorting out on the fin. This only happened at uncertain times because it had to vibrate over to the fin. Who knew? Even Harley was amazed because it looked perfectly normal otherwise.

  15. Marlon Sampang
    Marlon Sampang

    My 2004 Sportster 1200C runs great for the first seven miles, then it sputters and misfires but does not stall or die. Spark plug # 2 always getting fouled-up. This sporty only has 500 miles on it. Please help.

  16. Michael

    I have an 87 evo FXSTC, on my last ride with a buddy, about 10 miles out my bike began to misfire, sputter, die out while riding, but then it would come back to life while moving. Also, when I throttle down and then up there would be a delayed response and all of a sudden it would lunge forward, making it difficult to control the bike. We stopped and changed out plugs with no results. As I limped back home it got progressively worse, to the point that it would stall each time I stopped which required to restart the bike. At one point, it ran normal again but only for about a mile or two. I’ve checked the voes and it checks out, though it closes on #2 of the vacuum gauge instead of 3 to 5 as to what I’ve read and heard. I’ve not checked the coil as of yet but will before I change anything out. Any advice I can get would be greatly appreciated.

  17. Kenneth Pate
    Kenneth Pate

    My 1990 Harley Davidson FLHS starts on one cylinder, Then catches up and runs on both Cylinders until it gets hot then it drops down to one again