20HP Merc slips INTO gear when revving

[km1125]

I have a ~1980 ish (not sure exactly, could be 81 or 82) 20HP Mercury 2 stroke that I got from a friend and have been 'rebuilding'. Cleaned carb and fuel pump, put in new impeller. Started it a couple times and it runs pretty good. Still needs some adjustment to idle smoothly.

However, twice now when I've been running it on the stand, if I rev it up in neutral it has automatically popped in drive. What could be causing this? Otherwise it seems to shift normally. There are noticeable detents when I shift from fwd to neutral to reverse with the motor not running. I have not been able to put it in the lake or on a boat but I was hoping to run it enough on the stand to get the idle down pat.

 

[racerone]

Are you running with water supplied to the pump impeller?---There may be an adjustment near the shift lever too.

 

[km1125]

Yes, I have it in a bucket with water up the ventilation plate. I am seeing water out the 'pee' hole and it does run ok except for the idle. I think I just need to get it warmed up and set the mixture and idle screws correctly.

The throttle does have a safety mechanism (my old Johnson had something similar), where it will not allow the throttle to go higher than about 25% in neutral or 25% in reverse, but if you are in forward you can get to 100%. Don't think that's impacting the shift problem though, but not 100% certain on that. When running it, I revved it in neutral a bit and it kicked into fwd and threw water all over (and broke my stand). Wouldn't want that to happen on a small boat!