RPM'S and pinging
#2
05-10-2012, 11:42 PM
looking at a dyno chart ( any dyno chart for any motor) follow the torque line. you will see that it rises, flattens, then falls off.
the best drivability will be found by selecting gears which allow the motor to be in the "flat" area.
the motor will then have the best mechanical advantage.
and not have to work so hard.
at this point the ignition timing will be more advanced, meaning better economy- depending on throttle position and engine vacuum*
older Harley models ( putt, putt, putt) had heavier flywheels which stored forward energy in between the power strokes of the cylinder, the ignition could be retarded more and the fuel mixture was typically over rich at idle.
current models are designed to idle higher for number of reason including emissions control and oiling.
pinging can be caused by overly lean mixture ( by mapping or air leak),
rough head castings or any metal protrusions into the cylinder which can get overly hot, incl. carbon deposit build up ( rarer with EFI)
too advanced ign timing
wrong heat range spark plugs
low octane fuel ( old fuel in which additives have evaporated away)
and high compression ratios
among other causes.
* When stock my 09 96" would ping at 2800~3200 rpm up a 6% grade, this was repeatable. Downshifting would solve this as would opening the throttle further which will retard the ignition timing**
After looking at ign timing and fuel octane I added nightrider.com xieds to slightly richen the mixture, problem solved.
** ignition timing needs to be retarded when the motor is under high load, which usually coincides with the throttle being opened suddenly, like to pass or accelerate quickly. when this happen vacuum drops in the intake tract, carb and some EFI models will sense this low vacuum and retard the timing accordingly
Mike
the best drivability will be found by selecting gears which allow the motor to be in the "flat" area.
the motor will then have the best mechanical advantage.
and not have to work so hard.
at this point the ignition timing will be more advanced, meaning better economy- depending on throttle position and engine vacuum*
older Harley models ( putt, putt, putt) had heavier flywheels which stored forward energy in between the power strokes of the cylinder, the ignition could be retarded more and the fuel mixture was typically over rich at idle.
current models are designed to idle higher for number of reason including emissions control and oiling.
pinging can be caused by overly lean mixture ( by mapping or air leak),
rough head castings or any metal protrusions into the cylinder which can get overly hot, incl. carbon deposit build up ( rarer with EFI)
too advanced ign timing
wrong heat range spark plugs
low octane fuel ( old fuel in which additives have evaporated away)
and high compression ratios
among other causes.
* When stock my 09 96" would ping at 2800~3200 rpm up a 6% grade, this was repeatable. Downshifting would solve this as would opening the throttle further which will retard the ignition timing**
After looking at ign timing and fuel octane I added nightrider.com xieds to slightly richen the mixture, problem solved.
** ignition timing needs to be retarded when the motor is under high load, which usually coincides with the throttle being opened suddenly, like to pass or accelerate quickly. when this happen vacuum drops in the intake tract, carb and some EFI models will sense this low vacuum and retard the timing accordingly
Mike
Last edited by mkguitar; 05-11-2012 at 12:54 AM.
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