Folks,

I posted a few questions a while ago... I have this motor:

http://www.oldmercs.com/196869merc1250.htm

(1969, 125 HP merc) and a 18.5" fiberglass boat (I dont know what
brand).

I finally tried the motor and it runs fine, changed all the spark
plugs, oil and did a compression test. Comprsssion is as follows:

cyl 1-5: 124-127 PSI
cyl 6: 121 PSI

I dont know how much compression this should have but it looks pretty
even.
The motos fires up instantly and nothing seems wrong with it ...

I put the boat in the water but it wouldnt go faster than 26 MPH ...
it does plane but wont go faster. One problem was that the throttle
linkage doenst open the carbs all the way, but when the carbs are all
manually opened (by a volunteer the boat will max out at 26 MPH.
The motor revs about 3500 rpm.

Now I wonder. How fast should an old (probably heavy) 18.5" boat
roughly go with a 125 HP OB? Is 26 MPH realistic or too slow?

How fast should this kind of a motor spin? I think it should be around
4500 rpm?


The prop is 18 or 19 pitch 3 blade Merc. The boat also comes with a 2
blade (pitch unknown) but it wont even go 10 mph with it...

What kind of pitch seems normal for this motor/boat combination?

Is this a matter of motor problems? Or wrong prop? The pre owner used
it for water skiing ... but I doubt he was skiing @ 26 MPH ... I also
dont think he would have 3 props (one brand new) which have much too
much pitch...

So I wonder if the problem is elsewhere ...

I will bring the boat to a merc dealer but from experience with
automotive dealers i know that you either fix your problems yourself
or they dont get fixed, so i am not too opimistic and am hopeing
anybody here has any ideas.


Matt

WOT on that motor is suppose to be between 5000 and 5600 rpm. If everything
is as good as you say, then you have the wrong size prop on it. Talk to your
local prop repair man and he should be able to make a recommendation for
you. If he is like mine, he will loan you a prop to try.

--
Bill
Chesapeake, Va


"Matt Lang" wrote in message
om...
Folks,

I posted a few questions a while ago... I have this motor:

http://www.oldmercs.com/196869merc1250.htm

(1969, 125 HP merc) and a 18.5" fiberglass boat (I dont know what
brand).

I finally tried the motor and it runs fine, changed all the spark
plugs, oil and did a compression test. Comprsssion is as follows:

cyl 1-5: 124-127 PSI
cyl 6: 121 PSI

I dont know how much compression this should have but it looks pretty
even.
The motos fires up instantly and nothing seems wrong with it ...

I put the boat in the water but it wouldnt go faster than 26 MPH ...
it does plane but wont go faster. One problem was that the throttle
linkage doenst open the carbs all the way, but when the carbs are all
manually opened (by a volunteer the boat will max out at 26 MPH.
The motor revs about 3500 rpm.

Now I wonder. How fast should an old (probably heavy) 18.5" boat
roughly go with a 125 HP OB? Is 26 MPH realistic or too slow?

How fast should this kind of a motor spin? I think it should be around
4500 rpm?


The prop is 18 or 19 pitch 3 blade Merc. The boat also comes with a 2
blade (pitch unknown) but it wont even go 10 mph with it...

What kind of pitch seems normal for this motor/boat combination?

Is this a matter of motor problems? Or wrong prop? The pre owner used
it for water skiing ... but I doubt he was skiing @ 26 MPH ... I also
dont think he would have 3 props (one brand new) which have much too
much pitch...

So I wonder if the problem is elsewhere ...

I will bring the boat to a merc dealer but from experience with
automotive dealers i know that you either fix your problems yourself
or they dont get fixed, so i am not too opimistic and am hopeing
anybody here has any ideas.


Matt

Matt Lang wrote:

Folks,

I posted a few questions a while ago... I have this motor:

http://www.oldmercs.com/196869merc1250.htm

(1969, 125 HP merc) and a 18.5" fiberglass boat (I dont know what
brand).

I finally tried the motor and it runs fine, changed all the spark
plugs, oil and did a compression test. Comprsssion is as follows:

cyl 1-5: 124-127 PSI
cyl 6: 121 PSI

I dont know how much compression this should have but it looks pretty
even.
The motos fires up instantly and nothing seems wrong with it ...

I put the boat in the water but it wouldnt go faster than 26 MPH ...
it does plane but wont go faster. One problem was that the throttle
linkage doenst open the carbs all the way, but when the carbs are all
manually opened (by a volunteer the boat will max out at 26 MPH.
The motor revs about 3500 rpm.

Now I wonder. How fast should an old (probably heavy) 18.5" boat
roughly go with a 125 HP OB? Is 26 MPH realistic or too slow?

How fast should this kind of a motor spin? I think it should be around
4500 rpm?


The prop is 18 or 19 pitch 3 blade Merc. The boat also comes with a 2
blade (pitch unknown) but it wont even go 10 mph with it...

What kind of pitch seems normal for this motor/boat combination?

Is this a matter of motor problems? Or wrong prop? The pre owner used
it for water skiing ... but I doubt he was skiing @ 26 MPH ... I also
dont think he would have 3 props (one brand new) which have much too
much pitch...

So I wonder if the problem is elsewhere ...

I will bring the boat to a merc dealer but from experience with
automotive dealers i know that you either fix your problems yourself
or they dont get fixed, so i am not too opimistic and am hopeing
anybody here has any ideas.


Matt

You should get your linkage fixed first. Ignition advance is a large
part of "throttle" travel on an outboard, and the carbs are timed to the
stator plate or distributor. Typically, the ignition is fully advanced
on larger outboards by mid-throttle, but on this Merc the ignition
advance should pick up the throttle shafts at about 8 degrees BTDC, and
travel with the carbs all the way to 34 degrees BTDC advanced when the
carbs will be wide open.

The engine has to be "running" to do this test with a timing light,
which is hard to do while moving & on the water, so the test must be
done while cranking instead, after the fuel has been run out of the
engine so it does not start.

Just flipping the carbs open at partial advance will not give you full
output.

Also, specs call for "no more than 15 psi variation between cylinders"
on this family of engines. You're in good shape here.

Rob

"WRH" wrote in message news:d6Zec.654$2e6.206@lakeread01...
WOT on that motor is suppose to be between 5000 and 5600 rpm. If everything
is as good as you say, then you have the wrong size prop on it. Talk to your
local prop repair man and he should be able to make a recommendation for
you. If he is like mine, he will loan you a prop to try.

What makes me wonder is why the guy who owned the boat before has 3
props, 2 pretty much brand new which dont work ... thats why i tend to
think something is wrong with the motor.



--
Bill
Chesapeake, Va


"Matt Lang" wrote in message
om...
Folks,

I posted a few questions a while ago... I have this motor:

http://www.oldmercs.com/196869merc1250.htm

(1969, 125 HP merc) and a 18.5" fiberglass boat (I dont know what
brand).

I finally tried the motor and it runs fine, changed all the spark
plugs, oil and did a compression test. Comprsssion is as follows:

cyl 1-5: 124-127 PSI
cyl 6: 121 PSI

I dont know how much compression this should have but it looks pretty
even.
The motos fires up instantly and nothing seems wrong with it ...

I put the boat in the water but it wouldnt go faster than 26 MPH ...
it does plane but wont go faster. One problem was that the throttle
linkage doenst open the carbs all the way, but when the carbs are all
manually opened (by a volunteer the boat will max out at 26 MPH.
The motor revs about 3500 rpm.

Now I wonder. How fast should an old (probably heavy) 18.5" boat
roughly go with a 125 HP OB? Is 26 MPH realistic or too slow?

How fast should this kind of a motor spin? I think it should be around
4500 rpm?


The prop is 18 or 19 pitch 3 blade Merc. The boat also comes with a 2
blade (pitch unknown) but it wont even go 10 mph with it...

What kind of pitch seems normal for this motor/boat combination?

Is this a matter of motor problems? Or wrong prop? The pre owner used
it for water skiing ... but I doubt he was skiing @ 26 MPH ... I also
dont think he would have 3 props (one brand new) which have much too
much pitch...

So I wonder if the problem is elsewhere ...

I will bring the boat to a merc dealer but from experience with
automotive dealers i know that you either fix your problems yourself
or they dont get fixed, so i am not too opimistic and am hopeing
anybody here has any ideas.


Matt

On the water we opened the throttle all the way and then turned the
ignition to change the timing, it made a difference but resulted in
the low top speed..

I will get the boat to the dealer but would like to know whats up with
the boat beforehand ..

How fast (roughly) is such a 18.5 boat with 125 HP supposed to go ?

Matt


You should get your linkage fixed first. Ignition advance is a large
part of "throttle" travel on an outboard, and the carbs are timed to the
stator plate or distributor. Typically, the ignition is fully advanced
on larger outboards by mid-throttle, but on this Merc the ignition
advance should pick up the throttle shafts at about 8 degrees BTDC, and
travel with the carbs all the way to 34 degrees BTDC advanced when the
carbs will be wide open.

The engine has to be "running" to do this test with a timing light,
which is hard to do while moving & on the water, so the test must be
done while cranking instead, after the fuel has been run out of the
engine so it does not start.

Just flipping the carbs open at partial advance will not give you full
output.

Also, specs call for "no more than 15 psi variation between cylinders"
on this family of engines. You're in good shape here.

Rob

Matt Lang wrote:
On the water we opened the throttle all the way and then turned the
ignition to change the timing, it made a difference but resulted in
the low top speed..

I will get the boat to the dealer but would like to know whats up with
the boat beforehand ..

How fast (roughly) is such a 18.5 boat with 125 HP supposed to go ?

Matt



Matt,

With about a 2:1 gear ratio give-or-take (I think these were 28:14 gear
sets) and a 17" cupped prop, you should be able to get 38-39 MPH at 5000
rpm on most any planing hull. With the Merc 125, and a good/lighter
hull, 42-43 MPH @ 5000 rpm is reasonable with a 19" prop.

I've seen Lake X test results, with the 90 hp 6 cyl on a lightweight
(Offshore 17 DSC) boat produce a best top speed of 50.1 MPH on radar
with a Merc 3 blade 23" stainless prop, and only turning 4400 rpm (two
on board - about 8 ft. ASL). They tried every reasonable prop in
inventory, this one produced top speed... kind of a weird power band.
Also, the mod-tri-hull starts to entrap air at 47-48, and it starts to
chine-walk, so this prop is just getting the boat fast enough for a
little lift hence the speed. It's kind of squirrelly to control at this
point too.

It was (still is) a great all around ski/sport boat with a cupped 17" on
it, it gets up into its designed full-throttle range nicely at its home
here at 1729 ft ASL, at about 41-42 MPH.

Rob

"Matt Lang" wrote in message
om...
On the water we opened the throttle all the way and then turned the
ignition to change the timing, it made a difference but resulted in
the low top speed..

I will get the boat to the dealer but would like to know whats up with
the boat beforehand ..

How fast (roughly) is such a 18.5 boat with 125 HP supposed to go ?

Matt


You should get your linkage fixed first. Ignition advance is a large
part of "throttle" travel on an outboard, and the carbs are timed to the
stator plate or distributor. Typically, the ignition is fully advanced
on larger outboards by mid-throttle, but on this Merc the ignition
advance should pick up the throttle shafts at about 8 degrees BTDC, and
travel with the carbs all the way to 34 degrees BTDC advanced when the
carbs will be wide open.

The engine has to be "running" to do this test with a timing light,
which is hard to do while moving & on the water, so the test must be
done while cranking instead, after the fuel has been run out of the
engine so it does not start.

Just flipping the carbs open at partial advance will not give you full
output.

Also, specs call for "no more than 15 psi variation between cylinders"
on this family of engines. You're in good shape here.

Rob

There used to be a guy who worked on these mercs who posted here as "clams
canino". A google would turn up his email. He also sells motors and parts
on ebay. You might want to contact him.

del cecchi