Re: 1971 Evinrude 50 hp Need help
Some of the OMC engines in that time period have a automatic choke feature, which is controlled by a thermal switch. When the motor is cold, the choke automatically engages the choke halfway. This feature, as well as the electric choke function in general, can be disabled via a mechanical choke lever on the motor. Try disabling the automatic choke feature with this lever, to see if it makes any difference - you may be getting the half step choke at a point when it is not needed, thereby enriching the mixture to the detriment of the motor.
OMC later recommended that this feature be disconnected, per the following Service Bulletin. If the manual lockout solves the problem, I would go ahead and disconnect the automatic feature. BTW, while I don't have a service manual for your motor, it looks like the thermal switch is located on the powerhead's exhaust cover, which is different than the three cylinder models, where it is located at the lower, port side of the cylinder head. You don't have to remove this switch - I'm just letting you know where it is as a point of interest.
If you disconnect the system, be sure to install the jumper, as indicated. If you don't, you will only get half actuation, when using the electric choke switch on the control box.
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