On Thu, 20 Mar 2008 14:01:05 -0700 (PDT), "
wrote:

I've got a Yanmar 2gm20 that I'm pretty convinced has a problem with
the governor (speed is not well controlled especially when it comes
under load). The seemingly easy path is to fiddle with the injection
limiter. However, there are a couple of things holding me back.
First, they put a wire seal on the adjuster back at the factory. I've
had the problem from day one so I suspect that they didn't get the
adjustment right, but still I figure they sealed it for a reason. I'm
no Japanese scholar but it may even say "Tom, keep your **** hands off
this!" So, will really bad things happen if I mess with the limiter?
Second, I'm not sure exactly how to go about making the adjustment
should I care to. The manual says "if the engine does not accelerate
smoothly turn the limiter slightly counter-clockwise." Good, that's
my problem. The drawing shows a cap nut, lock nut and injection
control shaft. I presume I have to remove the nuts and back the
injection control shaft off a fraction. But, the drawing doesn't show
a slot or anything on the control shaft to keep it from turning while
I move the nuts. Is there some trick to making this work I should know
about when I attempt this? It'd be really nice if I could mark things
so I could at least get back to the current settings if fiddling
doesn't fix things. But how? Thanks!

-- Tom.

First, yes, fiddling with the governor can cause the engine to
explode.

The seals were put on the governor for a reason.

It is doubtful that the factory adjusted the governor incorrectly..

I suggest that you first adjust the idle speed to about 900-1000 RPM
in neutral and check that the high speed RPM is 3600 RPM in neutral.

Once you get these settings made does the engine seem to run normally?

If so, try the same settings with the transmission in forward. Your
idle speed should be essentially the same but high RPM may be a few
hundred RPM lower. If you can't reach full RPM and you have black
smoke coming out the exhaust then your prop is too big. If you can't
reach full RPM and no black smoke then you may have clogged filters -
change them all and try again.

If this doesn't cure your problem then frankly (and not to make fun of
you) from your questions I would suggest that you would be advised to
get a proper mechanic to have a look at things.

Bruce-in-Bangkok
(correct email address for reply)