merc 40 hp switch box

[JP102]

1980 merc 40 hp 2 cylinder.

Has anyone seen a bad switch box cause a motor to rev very high. Idles ok until throttle is engaged and when the throttle is pulled back to idle, the engine idles very high. A couple of times, the key would not shut the engine down when it happened.

On this motor, what limits the revs? I cannot find a reference to a vacuum cutoff or rev limiter for this motor.

 

[fastjeff]

No rev limiter. I suspect the carb butterfly linkage is sticking. If so, they don't start very well with the carb open and the throttle closed.

Jeff

 

[JP102]

Jeff, can you expand more on the carb being open and the throttle closed. Thanks

 

[fastjeff]

To start, the throttle needs to be about 1/4 open (on spark advance only) with the carb closed.

Jeff

 

[racerone]

1/4 open , but carb closed.----------------Or do you mean CHOKE CLOSED.

 

[galamb]

No, if you take a look at the linkage with the motor not running, and start to advance the throttle, the first thing that you will note is the throttle arm linkage to the trigger starts to move. Next, as you continue to advance the throttle, the arm hit's the (stop) that starts to open the butterfly in the carb.

So, the timing has advanced before you "open" the carb throat.