Rough Running Under Acceleration

Discussion in 'Engine, Fuel and Exhaust' started by threesteps, Mar 13, 2009.

  1. threesteps

    threesteps Junior Member

    I’ll apologize up front for the length of this post but I wanted to included all the info I could think of.

    Carbed bike, stage 1, V&H straight shots with Big City Thunder baffles done in '03, installed gear drives for cams and mild cam in 2006. Bike has always run well. The bike has been at operating temps when I experienced the rough running described below.

    Last weekend I noticed my bike had a momentary engine stall/pop when I did a relatively hard acceleration in 5th gear at about 2700-2800 rpm and 75 degree temp. Noticed this pop once throughout a five hour ride. On Monday I had been riding about 10-12 miles and when I rapidly move the throttle to full or very near full “open” as I started to pass a car (5th gear, approx 2800 rpm, Temp around 70 degrees). The bike started accelerating and then the engine began to pop/stall (cutting out) quiet a bit. I was able to repeat this at the same rpm range and gear.

    Next morning, bike would crank but not start. Noticed the enricher would not stay out during crank. Held enricher out and bike started.

    Road bike about 12 miles and was able to repeat previous rough running the next morning. Rapidly move throttle to open at same rpm settings as before, , and temp around 60 degrees. Pop/stall set in as before.

    Checked for intake leaks as described in Glider’s “Finding An Intake Leak” post. Negative leak indicated.

    Took bike to local dealer. Dealer checked for intake leaks—negative leaks. Told enricher was adjusted…assume they meant the “friction” on the enricher. Put on Dyno and they found the fuel/air mix would go lean, rich then lean during the same rapid acceleration in the same rpm and gear range as I’ve mentioned. Re-jetted the carb (don’t have size change on the jets). Dyno'd more to tune the carb and ignition (SE selectable map ignition system).

    Told bike fixed. Picked up bike, left it at closed dealer while the wife and I went to dinner. Enricher again move closed on cold start attempt. Bike ran better but still got one stall/pop during several acceleration runs on ride home. Also noticed my idle RPM is now at 1400 rpm after bike is warmed up.

    Will take bike back to dealer Monday. Could an enricher problem play in this pop/stall problem? Any suggestions as to what might be causing my problems? Any suggestion on steps to take from here?

    By the way, the dealer has been leaning over backwards trying to fix this. Lots of time spent. Very resonable charges.
  2. glider

    glider Veteran Member

    Your problem sounds like a transition problem between the stages in the carb where it changes over from one circuit to the other. It also sounds like the dealer by virtue of what you say about the enrichment adjustment doesn't know what they are doing. It's a PLASTIC nut behind the knob that just gets snugged a tiny bit to hold the enricher on when needed.Be gentle with it, they break easily.
    Adjusting Choke Knob Tension - Harley Davidson Community

    You may also try draining the float bowl using the help in this post. It may be a good time to start fresh and remove and clean out the tank as well as the float bowl and strainer from your symptoms.

    *Poor Performance With Carb Models - Harley Davidson Community

    You may also have other contributing factors like the slide being drilled that causes the lift to happen suddenly in some temps and can contribute to a problem like you are having.
  3. threesteps

    threesteps Junior Member

    Believe I've got the enricher properly adjusted.

    Looks like my carb doesn't have the screw to drain the bowl. Appears the hole where the screw should be has been capped/filled at the factory. Talked with the mech. at HD who worked on my bike. He had taken the bowl off and cleaned it out. Said bowl looked clean from the get go.

    Still studying the ins/outs of removing and flushing the tank.

    Thanks for your help.
  4. Caper

    Caper Active Member

    Take the air cleaner off and twist the should get a good squirt of gas...if not check the accelerator pump diaphragm for cracks or holes.