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Setting the timing advance at full throttle, 1985 25HP

M

mcdgary

Member
On my 1985 25 HP the timing instructions for the timing advance is to put boat in water,*put in gear and go full throttle and adjust timing advance link rod to*align*dots with*reference mark.* I have done this and secured both ends of boat to a concrete pier, and it's scary as h*ll.
*
If I take prop off (load removed from the motor)*and immerse motor in a water tank in my yard how much and which direction will I be off*as far as retarded or advanced?***By removing prop I've taking the load off the prop, but even still at full throttle it sounds like the motor is about to disintegrate.* I found out byleaving the prop on all the water is*immediately blown out of my tank.*
 
Re: Setting the timing advance at full throttle

You may indeed blow up the motor and it proves nothing.----------------------------Timing on outboard motors generally does not go out of adjustment.-------------Why do you feel you need to check / adjust it.--------------My best advice !---Find a dealer with a test prop or big test tank to check this for you.
 
Re: Setting the timing advance at full throttle

Agree with the above - you can not properly time max with the boat tied to a pier or still sitting on a trailer. Also, without the prop in place the engine can "run away" and kill itself (from over-revving with no load).

As noted, normally it's set in a test tank with a test prop (kinda looks like a big version of the disks you see in food processors for cutting up veggies :)). Alternately, on electric start models you can generally set the timing about 6 degrees high at "cranking" speed and it will be "close enough" under normal operation.

I also have some notes on older 25 horse (rope starts) that state you can set the max timing to 28 degrees BTDC at 3000 rpms and it will be retarded correctly to 25 degrees at 5500 rpms - so with the help of a buddy, and being careful, that should be possible while the boat is underway....
 
Re: Setting the timing advance at full throttle

galamb said:
Agree with the above - you can not properly time max with the boat tied to a pier or still sitting on a trailer. Also, without the prop in place the engine can "run away" and kill itself (from over-revving with no load).

As noted, normally it's set in a test tank with a test prop (kinda looks like a big version of the disks you see in food processors for cutting up veggies :)). Alternately, on electric start models you can generally set the timing about 6 degrees high at "cranking" speed and it will be "close enough" under normal operation.

I also have some notes on older 25 horse (rope starts) that state you can set the max timing to 28 degrees BTDC at 3000 rpms and it will be retarded correctly to 25 degrees at 5500 rpms - so with the help of a buddy, and being careful, that should be possible while the boat is underway....
Click to expand...
Thanks for the cogent post. I'm electric start and I have been thinking in that 6 deg. forward. I once made a prop with no pitch, which loaded the motor
with no forward thrust, may try that again. My advance timing link rod was removed, turned out of its correct position - dumb move.
 
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