On Thu, 20 Mar 2008 22:22:42 -0700 (PDT), "
wrote:
On Mar 20, 5:55 pm, Bruce in Bangkok wrote:
First, yes, fiddling with the governor can cause the engine to
explode.
Just to make sure we're on the same page, I'm not planning on messing
with the no-load maximum speed limiter. That's just fine and the
manual says, more or less, don't mess. I'm looking at the injection
limiter which is also sealed but which shouldn't change the ultimate
rpms and which the manual provides a method for adjusting... No, no,
don't hold back, I can take it 
Really, thanks for the input.
-- Tom.
I finally located a 2GM20 manual. downloaded it from
http://motoren.ath.cx/menus/yanmar.html
and "limiter" IS a "anmar"word.
The Manual quite emphatically states that the high speed adjustment
and the Fuel Injection Limiter should not be adjusted and will void
the guarantee if the seal is broken.
The screw labeled "No Load Maximum Speed Limiter" adjusts the linkage
to adjust the high RPM. The "Fuel injection Limiter" acts as a stop to
limit the maximum movement of the fork that moves the fuel rack that
determines how much fuel the individual injection pumps inject.
If, for example, the engine is idling and you jam the throttle full
open the Speed Control Lever applies force to the Governor Spring
which forces the Governor Lever to pull the rack (in the injection
pump) to the high fuel position and feeding more fuel to the engine
which causes the engine to accelerate. When the engine RPM reaches the
speed dictated by the tension of the Governor Spring the Governor
Weights swing outward and force the Governor Lever back against the
force of the Governor Spring to maintain the RPM selected by the
position of the Fuel Control Lever acting through the Governor Spring.
However, prior to the Governor Weights opening there is nothing to
resist the pull of the Governor Spring so the "Fuel Injection Limiter"
comes into play and acts as a stop to limit maximum movement of the
Governor Lever before the engine accelerates to a speed sufficient to
actuate the Governor Weights.
I'm not sure whether the Fuel Injection Limiter has a spring loaded
plunger in it or not. Detroit Diesel engines had a similar device but
in their case it was to limit surge at idle.
Backing the Fuel Injection Limiter out will increase amount of fuel
during acceleration before the Governor Weights have a chance to react
and thus the chance of over revving the engine is increased. Screwing
it in will reduce the amount of fuel and the engine will accelerate
slower then normal.
I'm certainly not going to recommend that you violate the
manufacturer's recommendations but if you are committed then hold the
safety wired nut and remove the acorn nut. The screw should have a
slot so it can be adjusted with a screw driver, if not scratch a line
on the screw so you can tell how far you have turned it.
First of all, with the boat securely tied to the dock (you don't
want to be charging all over the ocean while you are trying to adjust
the engine) try moving the throttle rapidly from idle to about half
throttle, with the transmission in neutral. You should get a puff of
black smoke and the engine should smoothly accelerate to whatever
speed your throttle is set to.
Backing the Fuel Injection Limiter out will increase the amount of
fuel available for acceleration and therefore a bigger puff of black
smoke.
Turning the screw in will reduce the amount of fuel available for
acceleration and reduce the puff of black smoke.
A normally operating diesel engine always has a little black smoke
when it accelerates.
If you reach a point that the engine accelerates to a higher RPM and
then settles back to a lower speed you have gone too far. Screw the
Fuel Injection Limiter back in a bit.
I would suggest moving the screw not more then a quarter turn at a
time.
Once things seem to work correctly try the same thing with the
transmission in gear and make any necessary adjustment.
Once you have the engine running properly when you accelerate to half
throttle try idle to full throttle (carefully). Once you have the idle
to full throttle acceleration adjusted both in neutral and in gear you
should have the engine correctly adjusted.
Bruce-in-Bangkok
(correct email address for reply)