Solution to low speed miss fire

Discussion in 'Engine, Fuel and Exhaust' started by NRA4LIFE, Jul 27, 2012.


    NRA4LIFE Member

    I wanted to share a solution to a problem I had on a 2002 FLHTCUI (27k miles). The bike had poor low speed performance at light throttle settings, rough idle, backfiring (the true definition). It ran decent under acceleration. It also had a rather nasty noise coming from the lower end area. An early Twin Cam with close to 30k on it, I figured bad cams, cam bearings, tappet roller(s) tensioners, etc. After reading the forum, it sounded like a vacuum leak, leaky internal fuel line might be the cause of the missfiring. I figured I better look into the engine noise first or a missfire would be the least of my worries. I pulled the cam cover and the tensioners were due, so I pulled the cams etc. The cams, cam bearings, tappet rollers all looked great. I put a wrench on the flat portion of the crankshaft and turned the engine a ways. It did not turn very smoothly at all. It had a notchiness (is that a real word :s) to it also. This got me thinking that it was like the rotor magnets were being felt. I pulled the primary and the compensationg sprocket was quite loose. I pulled the rest of the primary drive parts and checked the stator and rotor for physical damage. They looked just fine. I ohm checked the stator for good measure and it checked good, so I buttoned everything up and noted that the crank now turned smoothly. I finished up the tensioner job and started the bike to check for vacuum leaks etc. It idled perfect. I test drove it and it ran great ! The noise was gone too. Apparently the loose compensating sprocket and or rotor being loose was causing some kind of disturbance to the bikes fuel injection system (Delphi). Maybe someone more familiar with fuel injection can explain why.
  2. 03ultra45385

    03ultra45385 Active Member

    A loose compensator will allow the weight of the primary chain and the clutchpack to rotate out of sync with the engines power strokes. This can cause a very rough idle, the looser it gets the worse the idle gets. For those with a fairing it will break the supports and even break the mounting inserts out of the fairing if let go long enough. If your dealer says your chain is loose and adjusts it and it is still idles rough and or you still hear a knocking when you first start it up, pull the primary cover and check the compensator nut.
    1 person likes this.
  3. llharr

    llharr Member

    Very good information, I did not know this. Thanks