Dad bought a '74 merc 9.8 (SN- 3924668) which starts OK and runs OK at low
speed, but will only run at high speed part of the time. When you open up
the throttle to wide open, the engine runs rough at about 30% power for a
while, then will all the sudden kick into full power. It may take only a
minute, or it may take 15 minutes to get to this point. Once at full
power, it runs fine until you reduce the power back to idle then the problem
occurs again. The problem is more pronounced when the engine is warm. It
acts like it's only running on one cylinder when at high speeds. Has anyone
experienced similar issues or have a recommended checklist to trouble shoot
this problem.

I'm sure it's either fuel or electrical, so to start, I thought I would
check to make sure the fuel system is clean and there is a good ground for
all electrical / ignition parts. I'm not very familiar with outboards
though....

Start with the easy stuff first... replace spark plugs. But you may to clean
the carbs out.


"Billl George" wrote in message
...
Dad bought a '74 merc 9.8 (SN- 3924668) which starts OK and runs OK at low
speed, but will only run at high speed part of the time. When you open
up the throttle to wide open, the engine runs rough at about 30% power for
a while, then will all the sudden kick into full power. It may take only
a minute, or it may take 15 minutes to get to this point. Once at full
power, it runs fine until you reduce the power back to idle then the
problem occurs again. The problem is more pronounced when the engine is
warm. It acts like it's only running on one cylinder when at high speeds.
Has anyone experienced similar issues or have a recommended checklist to
trouble shoot this problem.

I'm sure it's either fuel or electrical, so to start, I thought I would
check to make sure the fuel system is clean and there is a good ground for
all electrical / ignition parts. I'm not very familiar with outboards
though....

As mentioned, it probably is the carb. I've been down that road.
Unfortunaley, carb cleaner didn't do it and I needed a complete rebuild.
This was a 1999 Mercury 40 HP that just sat too long without Stabil in
the gas.

Dan

Billl George wrote:

Dad bought a '74 merc 9.8 (SN- 3924668) which starts OK and runs OK at low
speed, but will only run at high speed part of the time. When you open up
the throttle to wide open, the engine runs rough at about 30% power for a
while, then will all the sudden kick into full power. It may take only a
minute, or it may take 15 minutes to get to this point. Once at full
power, it runs fine until you reduce the power back to idle then the problem
occurs again. The problem is more pronounced when the engine is warm. It
acts like it's only running on one cylinder when at high speeds. Has anyone
experienced similar issues or have a recommended checklist to trouble shoot
this problem.

I'm sure it's either fuel or electrical, so to start, I thought I would
check to make sure the fuel system is clean and there is a good ground for
all electrical / ignition parts. I'm not very familiar with outboards
though....

BTW - You will be lucky if it's a gummed up carb. The next problem to
look at is the stator and they are big bucks.

Dan

Billl George wrote:

Dad bought a '74 merc 9.8 (SN- 3924668) which starts OK and runs OK at low
speed, but will only run at high speed part of the time. When you open up
the throttle to wide open, the engine runs rough at about 30% power for a
while, then will all the sudden kick into full power. It may take only a
minute, or it may take 15 minutes to get to this point. Once at full
power, it runs fine until you reduce the power back to idle then the problem
occurs again. The problem is more pronounced when the engine is warm. It
acts like it's only running on one cylinder when at high speeds. Has anyone
experienced similar issues or have a recommended checklist to trouble shoot
this problem.

I'm sure it's either fuel or electrical, so to start, I thought I would
check to make sure the fuel system is clean and there is a good ground for
all electrical / ignition parts. I'm not very familiar with outboards
though....

I inspected the carb today and it looked clean with no signs of varnish,
etc. Fuel filter also looks fine. Plugs are new. I think he will try
to sell / trade this off to someone who want more of a challenge than he
does.


"Dan Krueger" wrote in message
nk.net...
BTW - You will be lucky if it's a gummed up carb. The next problem to
look at is the stator and they are big bucks.

Dan

Billl George wrote:

Dad bought a '74 merc 9.8 (SN- 3924668) which starts OK and runs OK at
low speed, but will only run at high speed part of the time. When you
open up the throttle to wide open, the engine runs rough at about 30%
power for a while, then will all the sudden kick into full power. It may
take only a minute, or it may take 15 minutes to get to this point.
Once at full power, it runs fine until you reduce the power back to idle
then the problem occurs again. The problem is more pronounced when the
engine is warm. It acts like it's only running on one cylinder when at
high speeds. Has anyone experienced similar issues or have a recommended
checklist to trouble shoot this problem.

I'm sure it's either fuel or electrical, so to start, I thought I would
check to make sure the fuel system is clean and there is a good ground
for all electrical / ignition parts. I'm not very familiar with
outboards though....

Dan Krueger wrote:
BTW - You will be lucky if it's a gummed up carb. The next problem to
look at is the stator and they are big bucks.

Dan

Billl George wrote:

Dad bought a '74 merc 9.8 (SN- 3924668) which starts OK and runs OK at
low speed, but will only run at high speed part of the time. When
you open up the throttle to wide open, the engine runs rough at about
30% power for a while, then will all the sudden kick into full power.
It may take only a minute, or it may take 15 minutes to get to this
point. Once at full power, it runs fine until you reduce the power
back to idle then the problem occurs again. The problem is more
pronounced when the engine is warm. It acts like it's only running on
one cylinder when at high speeds. Has anyone experienced similar
issues or have a recommended checklist to trouble shoot this problem.

I'm sure it's either fuel or electrical, so to start, I thought I
would check to make sure the fuel system is clean and there is a good
ground for all electrical / ignition parts. I'm not very familiar
with outboards though....




9.8? Yup, you're looking at a stator and/or trigger. They're known for
that malady.

Rob