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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12275
Experience:  25+ yrs. experience
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I have a 2014 CRF250L dual sport motorcycle, the ignition fires

Customer Question

I have a 2014 CRF250L dual sport motorcycle, the ignition fires every 720 degrees or rotation, how does the ECM decide when to fire the ignition without a cam position sensor?
Submitted: 2 years ago.
Category: Motorcycle
Expert:  Louie replied 2 years ago.
Hi and welcome to JustAnswer,
Thank you for the question and your patience. Should you still need assistance for information purposes only...
Initially, the CRF250L uses a CKP (crankshaft position) sensor. This sensor is co-located at the stator/alternator area and sends pulses to pin 23 of the ECM.
Customer: replied 2 years ago.
that gives a signal every rotation of the crank, the ignition coil only fires every other rotation of the crank, the service manual does not say how that is determined.
I have a electronic tachometer, that is how I discovered the firing interval.
Expert:  Louie replied 2 years ago.
Is the electronic tachometer calibrated/designed for a single cylinder/motorcycle engine? ...or for 4 or more cylinders.
Customer: replied 2 years ago.
it is a bike master (266266) combination hour meter tachometer made by KOSO, and it is capable of multiple cylinders.
it came set for 1 pulse per revolution but it indicated twice the actual engine speed. it showed a warm idle speed of nearly 2900 RPM, changing the setting to 0.5 pulse per RPM brought the indicated engine speed down to where it needed to be with a indicated warm idle of 1420rpm, what the factory manual calls for the idle to be.
Expert:  Louie replied 2 years ago.
I understand.Still, the location of the 720° is the same as that of the 360° and the 0° hence if it fired in 720° position, then it would have also fired on/during the 360° and the 0° positions.It would not be practical nor possible for a single cylinder engine to fire on every second rotation of the crank.Based on the above, the engine is firing every 360° actual.
Customer: replied 2 years ago.
I would have though so also, and the instructions for the tach stated that single cylinder engines normaly fire every rotation of the crank shaft, but it did not read correct and they programed the tach to work on engines that fire every other rotation like Honda small singles like the mini trail that are triggered by the cam shaft.
Expert:  Louie replied 2 years ago.
The "...changing the setting to 0.5 pulse per RPM..." would be very significant as it would also refer to halving (X 0.5) the reading for the 720° or = 360°.

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