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My motor is a Yamaha 1999 40HP, non oil injected (model C40TLRX) that I bought used last fall. I swapped out the lower unit with an aftermarket jet kit. I didn't change any throttle or timing adjustments since the motor started, ran and idled well, although the idle was a little higher than spec.
When I first added the jet kit, the motor ran at 5100 WOT when cold and dropped to 5000 after running for about 10 minutes. The last several times out the motor would start out at 5000 and drop to 4900. This weekend I decided to check the settings and see if I could determine the cause of the drop in RPM.
The compression was 115, 115 & 110 from top to bottom cylinders.
I found that the throttle was not opening fully when the throttle control was fully forward. I started checking the settings and found that the static timing adjustment was out of spec (distance between measuring points was 25MM instead of 20MM called for). The full retard and full advance timing were both too high according to the marks on the CDI box. After I made the static timing adjustment, the full retard and full advance settings were correct according to the marks on the CDI, but the throttle was even farther from fully opening. So I made all the checks and adjustments called for in the Clymer Manual in the Timing, Synchronization and Adjustment section for my motor, except for ignition timing and the pickup timing. I had no way to run the motor out of water to perform these checks and adjustments according to the directions. So I simply adjusted the throttle roller (cam follower) closer to the throttle arm (cam) so that the throttle would open fully when the throttle control was fully forward. Is this an acceptable procedure?
I haven't had a chance to run the boat yet and check the settings with a timing light. I assume that the proper procedure would be to set the timing at idle and WOT to the specs in the manual no matter what the markings on the CDI box indicate. Is this correct?
Another question, does the throttle arm wear over time? It appears to me that mine is worn. I can see no other explanation as to why the throttles weren't opening fully, since I had made no changes.
Thanks,
Larry
When I first added the jet kit, the motor ran at 5100 WOT when cold and dropped to 5000 after running for about 10 minutes. The last several times out the motor would start out at 5000 and drop to 4900. This weekend I decided to check the settings and see if I could determine the cause of the drop in RPM.
The compression was 115, 115 & 110 from top to bottom cylinders.
I found that the throttle was not opening fully when the throttle control was fully forward. I started checking the settings and found that the static timing adjustment was out of spec (distance between measuring points was 25MM instead of 20MM called for). The full retard and full advance timing were both too high according to the marks on the CDI box. After I made the static timing adjustment, the full retard and full advance settings were correct according to the marks on the CDI, but the throttle was even farther from fully opening. So I made all the checks and adjustments called for in the Clymer Manual in the Timing, Synchronization and Adjustment section for my motor, except for ignition timing and the pickup timing. I had no way to run the motor out of water to perform these checks and adjustments according to the directions. So I simply adjusted the throttle roller (cam follower) closer to the throttle arm (cam) so that the throttle would open fully when the throttle control was fully forward. Is this an acceptable procedure?
I haven't had a chance to run the boat yet and check the settings with a timing light. I assume that the proper procedure would be to set the timing at idle and WOT to the specs in the manual no matter what the markings on the CDI box indicate. Is this correct?
Another question, does the throttle arm wear over time? It appears to me that mine is worn. I can see no other explanation as to why the throttles weren't opening fully, since I had made no changes.
Thanks,
Larry
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