Re: [OMC-Boats] timing/carb adjustment

From: Lee Shuster <lee.k.shuster@...>
Date: Tue, 29 Jul 2008 11:43:16 -0600

Hi Jeff,

I'd like to ask a couple of "dumb" questions:

>> So a short history on my boat: had "different" Buick 155 put in my
boat last winter.

Do you know the history or source of your "different" Buick V6? Is it a
225 Cu in or 231 Cu in?
It's a long shot but --- You could have a even-fire crankshaft (231)
engine which requires a different distributor. Stay with me:

The original OMC Buick V6's were all odd-fire and were 225 cu in. They
used Delco-Remy distributors designed specifically for the odd-fire 225
cu in. Buick engineers first introduced the 90-degree "Fireball" 198 CID
V6 for the Buick Special & Skylark in 1961. In 1964 Buick bumped the
V6's displacement to 225 CID. The 90-degree 225 CID V6 engine was
essentially the 300 CID V8 with two cylinders removed. Odd-fire V6
firing intervals were staggered at 90 and 150 degrees so the tooling
could be shared with the V8. A 231 CID odd-fire V6 was offered from '76
- '78.

For smoother idling, Buick switched to a (weaker) split-pin crankshaft,
resulting in an even-firing V6 with the 231 & 252 CID V6's midway
through the 1977 model year and later. Even firing 6's use 120 degree
intervals. Hard for the average car mechanic to tell the difference
from external appearances.

(Look at the distributor cap and you'll see the rather "odd" odd-fire
spacing, 90-150-90-150-90-150.) See my website for more details on the
odd-fire/even-fire Buick V6:

If you want a more detailed explanation on the odd-fire oddities see:

Was your "mechanic" a car guy or an experienced OMC marine guy?

Your used Mallory Marine distributor? Is it possible you got an
even-fire V6 distributor and stuck it into your odd-fire? Check the
inside of the distributor cap: Evenly spaced 6's are
120-120-120-120-120-120 degrees apart. I have never heard of a Mallory
distributor being used on an odd-fire Buick, but I suppose anything is
possible. Also, re-check the firing order: The odd-fire firing order is
1-6-5-4-3-2. The even-numbered cylinders are starboard, while the
odd-numbered cylinders are port-side. The heads feature an unusual valve
arrangement: E-I-E-I-I-E (port bank, stated from front to rear, or
starboard bank, stated from rear to front.) (Where Even-fire Firing
Order is: 1-6-3-5-2-4)

There's some very strange possibilities going on here -- This thread is
beginning to remind we of Click & Clack!

Hang in there -- I'm just trying to help out by figuring out exactly
what you have. Do you have a SELOC or OMC shop manual? that would be

Oh yeah, what carb do you have? OMC used both 1-barrel (1964-65) and
2-barrels (1966 - 1970). I think the 1-barrel's were Carter's and the
2-barrels were Rochester's.

Lee Shuster
Salt City

-----Original Message-----
From: omc-boats-bounces@...
[mailto:omc-boats-bounces@...] On Behalf Of JEFF DOOD
Sent: Tuesday, July 29, 2008 10:00 AM
To: Evinrude & Johnson Boats of the 1960's and 70's
Subject: Re: [OMC-Boats] timing/carb adjustment 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
> > _______________________________________________
> > OMC-Boats mailing list
> > OMC-Boats@...
> >
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