Re: [OMC-Boats] timing/carb adjustment

From: JEFF DOOD <jdood@...>
Date: Tue, 29 Jul 2008 09:00:28 -0700 many applicable topics on this list to what i'm going through
with my boat right now. first off, i have a mechanic, but i dread
having to leave my boat with him because i usually don't see it for
another month. So i have been crash coursing myself to try learn
about my engine and work on it myself as much as possible. i am
good with cars, great with electrical stuff. boat engine stuff - so
so. and when it gets into timing and carb adjustment i am really
feeling my way through it. i haven't even done that on a car yet.

So a short history on my boat: had "different" Buick 155 put in my
boat last winter. mechanic got it running, starting, but never water
tested. a few weeks back took it out for test, started fine, ran
ok at low speed, but lost all power at about 10mph. He thought
carb rebuild needed. i rebuilt carb that weekend. test ran and
still had same problem. Although adjusting it was kind of a guessing
game. My mechanic said to screw the two adjustment screws in all the
way until the engine almost stalls, then back them out about a turn
and a half. he also said to do this while boat was underway, not
idling in neutral. Well i did this, and had the screws in about
every conceivable position and always the same thing - no power at
about 10 mph.

  So back to the dock i slowly went. Random guy at the dock
suggested it might be a bad distributer. (mechanic didn't bother
telling me i had a car distributer on there). So i got a used but
good condition, SUPPOSEDLY original Mallory distributer. replaced
points, condenser, installed this past weekend. Went to dock to for
timing last night. (First time i have ever timed anything). Got
it started, idled alittle rough but nothing major. Twisted the
distributer and got the white mark to mostly line up with the "5" as
spec'd in the manual. Seemed to smooth out idle at first. Then i
played with carb screws again. Double checked timing, etc etc.
End result is same thing, except maybe a little worse. now idles a
little rough and stalls out at about 10 mph.

Any suggestions?

When setting the timing, is the white mark that is to be line up
with the "5" supposed to bounce all over making it really difficult to
line up exactly?

how important is the tach in this process? i have no working
tach. But in theory, shouldn't i be able to get things get pretty
close by just listening to the engine?

am i adjusting the carb correctly? is there a sequence to
adjusting all this stuff - carb then timing? timing then carb?

if i end up having to replace the carb altogether, is there an source
for those out there? new? used?

would sure love to use my boat this summer!

thanks, jeff

On Jul 28, 2008, at 1:58 PM, Don Mandelas wrote:

> Ethan, I undertsand what your saying. I'll recheck the RPMs with
> the timing light again and double check the settings. (I'll re-do
> the test so that I'm confident with the results). Maybe I'll even
> get the tinytach you were talking about.
> Don.
> > Date: Mon, 28 Jul 2008 13:42:35 -0500
> > From: brodskye@...
> > To: omc-boats@...
> > Subject: Re: [OMC-Boats] Engine RPM and Boat Speed
> >
> > On Sun, 27 Jul 2008, Don Mandelas wrote:
> > > This weekend I was able to obtained a timing light and digitally
> measure
> > > the revalutions per minute of my V-6 155 hp boat engine.
> > > I discovered that when the timing light indicated 1,100 RPM's my
> boat
> > > tachometer was reading 1,000 RPM's. And, when the timing light
> indicated
> > > 4,000 RPM's my boat tachometer was reading 3,000 RPM's. This
> means my
> > > tachometer is reading a full 1,000 rpms below what it should be
> on the
> > > higher end of the scale and is probably the primary reason why I
> am going
> > > slower than normal. I'll replace the tachometer and try the boat
> again.
> >
> > This sounds a little strange - you say that the tach is reading
> low, so the
> > engine is actually spinning faster (and making more power) than
> believed.
> >
> > I found the opposite on mine - when I measure the RPM (using a
> TinyTach
> > inductive pick-up on a spark wire), I see that the tach is reading
> > substantially high (1000-1500 rpm). My understanding is that older
> tachs
> > tend to read high due to weakening of the return spring with age.
> >
> > Are you sure you had the timing light set properly (some can be
> switched
> > between various combinations of two-stroke/four-stroke, single/multi
> > cylinder, and wasted-spark modes) and it wasn't reading high by a
> factor of
> > two? I'm not sure how it works with older distributors, whether
> each spark
> > plug fires once for every revolution or just every second time. I
> think
> > it's the latter.
> >
> > Tinytachs are a fairly cheap way to have a more accurate RPM
> reading, as
> > well as an hour-meter. Unfortunately I don't remember whether the
> 4C or
> > the 2C should be used.
> >
> >
> > If anyone has figured out a way to adjust the factory OMC facts,
> I'd like
> > to fix mine. I haven't figured out how to do that yet.
> >
> > Ethan
> >
> > --
> > Ethan Brodsky
> > _______________________________________________
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> > OMC-Boats@...
> >
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Received on Tuesday, 29 July 2008

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