9.9 to 20 hp parts

[KKBoater]

I recently changed the flame arrestor and seal which greatly improved getting on plane and speed. I did not replace the ECU. Is this important? I've seen posts stating that a new ECU is needed AND some that say the new ECU is not needed. I don't want to damage the motor. Thank you for your replies.

 

[William01]

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Not your family of engines but it might work in your case

 

[Tommy2t]

The ecu controls the max RPM which i think is 6000 on the 20hp it also controls the fueling., Different part #'s so i would think it is necessary.

 

[dmw]

I recently changed the flame arrestor and seal which greatly improved getting on plane and speed. I did not replace the ECU. Is this important? I've seen posts stating that a new ECU is needed AND some that say the new ECU is not needed. I don't want to damage the motor. Thank you for your replies.

Have you had any issues not chaning out the ECU? Does it ever run hot or rough? Thanks!

 

[kevinj]

Have you had any issues not chaning out the ECU? Does it ever run hot or rough? Thanks!

You really should change the ECM when the throttle plate restrictor is changed as well. Max RPM is not the only difference in the ECM's. The ECM fuel mapping is matched to throttle position and the airflow delivered by the restrictor. If you have a 20HP restrictor and a 9.9 ECM you are delivering more air to the engine than the ECM is programmed to deliver fuel, so you're effectively running a lean mixture.