Venting, Charging System, Ignition

Q: Dear Fix My Hog,
I always read your e-mails! I have your Fix MY Hog DVDs for my cruiser. I also own the manual by Haynes Service & Repair for the Sportster
1970-2008 models.

I have a 2002, HD 1200 Sportster, Custom

The problem : On longer rides (> 8 miles) the bike suddenly begins to miss fire – so badly that it often cuts out, then after a brief rest period it works perfectly, only for a short time before repeating the cycle, on a previous occasion it rode longer each time this cycle repeated but this last time it limped home miss firing.

What I have done so far:
Repaired the rubber hoses to the tank/carburetor section – breather tubes/fuel diaphragm tube, etc
Cleaned the fuel filter & Tank. Install new plugs – the new fancy type that has no adjustable electrode gap overhauled the carburetor (It is now set to run just a little leaner than before). I checked the wires to – the ignition, regulator, coil and plugs. I have reset the primary chain tension by adjusting the nut to give the tension advised in the manual (but I noticed that I had to reset it again yesterday.)

My first suspicion was that I had a fuel supply and control problem!
– since then I have focused on timing & ignition areas. By the time you read this I will have changed the oil and the oil filter. (the level is OK, but oil could do with a change)
Do let me know what you think the problem is.
Thanks for your assistance in advance,
Over & Out

A: George, a few things. First is easy. Make sure that the gas cap is venting correctly. If You put it to your mouth, you should be able to suck air thru it. Next, test your charging system. If that checks out. I would look at your ignition. Make a jumper wire. You will need 1 small eyeloop (for coil terminal), 1 larger eyeloop (for battery positive post), 1 male spade terminal, 1 female, and maybe, 3 feet of wire. Run the wire from the coil post where the white wire was (remove the white wire for now), to the positive battery post. The spade terminals should be in line where you can easily get to them. The spade terminals will be your “quick disconnect”. Ride your bike this way. *Remember you will only be able to turn off the bike by disconnecting the jumper (pull apart the spade terminals). Wiring the coil this way isolates your ignition from the rest of the bikes electrical system. If your problem persists; your ignition is, more than likely, the culprit. If this seems to stop the problem, something else in your bikes electrical system is effecting your ignition system.

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8 Responses to “Venting, Charging System, Ignition”
  1. C Dennis
    C Dennis

    I have posed this question 3 tims now and as yet recieved a response. That or been unable to find it. Going to give it one last chance, then I’ll try other sights. I have a 99 sporster with an 03 1200 cc motor. The bike starts easily and will run fine for maybe a mile. Then there is a rapid loss of power & it quits. After sitting for 10 to 20 min. it will occasionally start back up olny to die again in less time than at first. Qhen this happens it will not start for hrs if not till the next day. I have drained the tank and used an air compressor to blow it out & air flows easily through the pitcock. I’ve also replaced the fuel lines & inline fuel filter. Also taken the stock carb apart and cleaned it. The coil test within spec. and have replaced the plug recently. Thw battery is less than 2 months old & is fully charged and well connected. What else should I do/ check/replace… Any help will be greatly appreciated, I haven’t been able to ride in over a month now & its driving me up the wall to see it just sit there every morning when it should be taking me to work then cruising with my boys. Thanks very much

    • Doug Schuelke
      Doug Schuelke

      When it dies pull the plugs and see if they are wet or dry and also check for spark. If plugs are dry it is likely fuel problem, if wet and no spark, ignition problem. Also try without air cleaner.

    • Danny Gray
      Danny Gray

      It appears to be your coil from your description. I know you said you tested it. Check for spark when you have the problem. It could be the ignition modal but I am leaning towards the coil.

  2. John

    I would check the tightness of your battery cables. My sportster did that same thing years ago and it was a loose cable at the battery.

  3. Tom P.
    Tom P.

    I had this same problem on my 88 Heritage. Turned out it was the ignition module (brain?). It must have had an internal problem that when it got hot, 5 or 8 miles down the road it would shut down. Replaced the module and it never happened again.

  4. Michael Abrams
    Michael Abrams

    A tube fell of my 2007 XL1200L. It has a few fittings on it like a check valve an a rubber elbow on the end near the fuel tank. What is it?