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VIPER 1100R - FAQ and Troubleshooting



My tachometer is erratic at idle. RPMs approximately double without throttle input.


Situation is related to the engine’s ignition and is usually not the tachometer.  Situation has been experienced in older engines using stock ignition and no ECU tachometer lead wire (e.g. the tachometer’s yellow lead wire is wrapped around the plug wire to obtain the signal).  This situation occurs because the ignition is sending an extra pulse.  This is a weak signal that is not enough to cause a backfire, but strong enough that it is registering on the tachometer - causing the RPM readout to be erratic, approximately doubling at idle. This additional weak pulse can often be verified using a timing light. 



Changes to the ignition system to eliminate the weak pulse are possible (specific to engine types).  While the preferred approach is to directly hook the tachometer up using the designated tachometer lead wire from the engines ECU, it is also acceptable to wrap the tachometer’s yellow lead wire around a plug wire in instances where no designated tachometer ECU lead wire is present.  In situations with an additional weak pulse, increasing the number of wraps (as many as 25) increases conductivity and the chances of filtering out the weak signal.  It is always recommended when wrapping the yellow tachometer lead wire around the plug wire that the yellow lead wire be secured to the plug wire with electrical tape or heat shrink wrap.

Description: Viper1100R erratic at idle; Viper 1100R idle bound; Acewell 1100 erratic at idle, Acewell 1100 idle bounce.
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