fuel enrichment explanition ??

[dtoole]

hi , i'm working on a 1999 40 hp yamaha . model # c40tlrx. my question is about the fuel enrichment system. what would be symptoms of a faulty solenoid ? or a ruptured diaphragm ? also on this model, what position should the manual valve be in ? (open or closed ) the owner brought the boat to me complaining about a lack of power, engine shutting off, and hesitating . i did the usual preliminary checks (compression and spark gap ) all good. i then tried to crank the motor to see how it was running. it would only fire up for a second and only at idle. after playing with it for awhile i found the manual valve on the fuel enrichment. i turned it and the motor cranked but ran pretty bad. i then contacted the owner to see if he had turned the valve . he said that he didnt even know it was there. so i thought the carbs were stopped up and that it was now running off the enrichment valve. so i went through the carbs. they were very clean. the slow jets were partially clogged. after reassembly the motor runs better but still not smooth and is smoking alot. i didnt see any problems with the diaphragm. just not sure how the system works. any comments are welcomed. thanks......david

 

[boscoe]

Automatic Enrichment
With the valve set in the automatic position, enrichment of the engine will take place depending on the temperature of the engine and the electrothermal
valve. Enrichment will take place automatically as outlined previously and as long as the throttle valves remain closed during cranking.

Manual Enrichment
When the manual enrichment lever is at the open position, the fuel is drawn by the enriching fuel pump and led directly to the intake manifold through the passage selection
valve. Air will not be drawn for primary mixture in this setting. When starting the engine with the manual enrichment lever open, the lever should be turned to the closed position immediately after the engine has started.

Manual Enrichment Closed
If the power source for the electrothermal valve should fail with the valve fully open or should the electrothermal valve fail to close, the manual enrichment lever should be turned to the closed position. After starting, the engine can be run normally with the valve in the closed position.