"Gene Kearns" wrote in message
...
On Sat, 14 Jun 2008 13:17:58 -0400, Jim penned the following well
considered thoughts to the readers of rec.boats:


"Gene Kearns" wrote in message
. ..
On Sat, 14 Jun 2008 08:43:05 -0700 (PDT), penned
the following well considered thoughts to the readers of rec.boats:

On Jun 14, 9:49 am, "jamesgangnc" wrote:
"Robert M. Gary" wrote in
...

Reading my shop manual for my 4.3L 190hp carb'd Merc I see that it
describes setting the "base timing" as well as the "ignition
timing".
Both procedures look almost the same so what is the difference?
Also, it says you must set the "Dwell" before timing the boat; what
is
that?

The procedure for setting idle and mix on the carb is very complex
in
the manual. They say you have to be in the water to do it. In old
cars
I would just set the mix about one turn rich of when the car started
to run rough and I'd set the idle based on the tach. Why can't you
do
the same on a boat?

-Robert

So you have confirmed that your boat has points? The service manual
only
covers your model?

Dwell is the point gap. Truth is that a feeler gauge is accurate
enough
for
setting the points. There is considerable tolerance. A timing light is
the
best way to set the time. Make sure the boat is at the correct idle
first.
Few boats have a vacuum advance but in the cases where they do it is
typical
to set the idle with it disconnected but your manual should specify.

Without actually seeing what they are suggesting for mixture setting I
can
only agree with you. I set my idle mixture and idle speed the same way
you
describe.

If you really have points then going through a good tune up, including
replacing the points and plugs is a good idea before looking deeper
into
your other problems. Plugs do not last nearly so long with point style
ignitions. You might make a note of how far off, if any, the timing is
before you start though since that will help you decide if the tune up
has a
chance of fixing your running hot problem.

You never answered, or I never saw it, do you use regular or premium?

Actually, dwell is expressed as an angle, and it is the measurement of
time the points or electronic module is in a closed state.

Dwell is accurately expressed in degrees..... but, point gap is a
function of that angle and the "dwell angle" can be approximated in
terms of point gap. (Distributors are always set by feeler gage before
using a dwell meter.)

Proper set-up of this particular distributor sounds like both a dwell
meter and an advance timing light would be necessary, unless you have
one of those old Snap-On distributor testing machines to set the
distributor RPM, gage the dwell, and watch the curve as you apply
vacuum and/or RPM. (And I am assuming some sort of vacuum or
mechanical advance is part of the assembly.)

--

Grady-White Gulfstream, out of Oak Island, NC.

Homepage
http://pamandgene.idleplay.net/

Rec.boats at Lee Yeaton's Bayguide
http://www.thebayguide.com/rec.boats


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I just looked it up. All Carbed 4.3L Mercruisers use Thunderbolt
ignitions.
No Points to bother with. No mechanical advance to bother with. No timing
to
set other than base timing.

That also means, then, I think..... that he has a Thunderbolt V
ignition and one must ground the "advance wires" to bring the
distributor into "base timing." If that isn't accomplished, the
computer will continue to screw around with your attempts to properly
set timing.

Unfortunately, successful timing of this engine is dependent on a
properly operating carb....

I'm confused as to why the OP's manual even refers to dwell, unless it
isn't the right manual......

--

Grady-White Gulfstream, out of Oak Island, NC.

Homepage
http://pamandgene.idleplay.net/

Rec.boats at Lee Yeaton's Bayguide
http://www.thebayguide.com/rec.boats


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Seloc And Clymer are notorious for putting several models in the same model
and not always giving proper reference when doing procedures. It's better to
have the OEM manual for the engine you have.
The OP could have a Thunderbolt 4 or 5 depending on year. If I recall as
long as RPM was 550 to 600 the base timing could be read without grounding
or shorting wires.