I had a similar problem on a different engine the weekend before last. I had
to keep pumping the bulb to limp back to port. The problem was the fuel
pump. An $11 rebuilt kit fixed the problem.

Tom

wrote in message
. ..
Hi everyone,
With the wealth of knowledge and experience here, I have a problem that
needs your insight.

My (new to me) Yamaha 9.9 HP outboard (built year 2000) usually runs
fine at lower RPM, but when I ramp up over 35% of max speed the engine
will invariably run fine for 20-40 seconds and then cough, sputter, slow
for a few seconds and then speed back up. The faster the RPM, the more
frequent the problem.

Sometimes pumping the sqeeze bulb on the fuel line will solve the
problem for a short while, but not always.

I immediately suspected a fuel line problem, but the filters are all
clean (in engine and in gas tank), the hose seems to be clear, and just
to make sure I also changed the spark plugs and oil.

The only think I can think of is that it could be sucking air somehow.

Any suggestions would be extremely welcome!

Thanks, and fair winds,
Mike

Thank you, everyone! The problem was a plugged vent- I got it cleared
last night and ran it smoothly for 15 minutes.
Mike

wrote:

Hi everyone,
With the wealth of knowledge and experience here, I have a problem that
needs your insight.

My (new to me) Yamaha 9.9 HP outboard (built year 2000) usually runs
fine at lower RPM, but when I ramp up over 35% of max speed the engine
will invariably run fine for 20-40 seconds and then cough, sputter, slow
for a few seconds and then speed back up. The faster the RPM, the more
frequent the problem.

Sometimes pumping the sqeeze bulb on the fuel line will solve the
problem for a short while, but not always.

I immediately suspected a fuel line problem, but the filters are all
clean (in engine and in gas tank), the hose seems to be clear, and just
to make sure I also changed the spark plugs and oil.

The only think I can think of is that it could be sucking air somehow.

Any suggestions would be extremely welcome!

Thanks, and fair winds,
Mike

On Thu, 22 Jul 2004 17:09:40 GMT, "
wrote:

Thank you, everyone! The problem was a plugged vent- I got it cleared
last night and ran it smoothly for 15 minutes.

It'll be truly fixed when you can run it for 15 NM in short chop. That
loosens the flakes and debris nicely, I find G

R.

Ah, if you are a pessimist you are never disappointed. I write that
with the utmost respect, Rhys, because I have experienced it too many
times in practice.

After 7 NM with moderate waves I got the problem back again. After much
more troubleshooting I found that I have a tiny oil leak somewhere.
Turns out the Yamaha 9.9 is designed to drop to low RPM's and run rough
when it senses a loss of oil pressure. After running at low RPM for a
short while enough oil was accumulating in the reservoir to allow oil
pressure to go back to normal, thus the intermittent nature of the problem.

A quart of oil and 10 NM later the "effect" seems to be gone, although I
still have to find the leak causing the problem.

Mike

rhys wrote:

On Thu, 22 Jul 2004 17:09:40 GMT, "
wrote:


Thank you, everyone! The problem was a plugged vent- I got it cleared
last night and ran it smoothly for 15 minutes.


It'll be truly fixed when you can run it for 15 NM in short chop. That
loosens the flakes and debris nicely, I find G

R.

On Wed, 28 Jul 2004 13:40:34 GMT, Mike_H
wrote:

A quart of oil and 10 NM later the "effect" seems to be gone, although I
still have to find the leak causing the problem.

Interesting. Does it leak at rest or only when under load? What I am
getting at is does the rising engine heat cause a gasket somewhere to
fail, or is it the rising oil pressure that forces oil past a hole or
gasket or crack or something that "closes" or reseats itself when the
motor cools down?

I'm glad you are getting closer to the ultimate problem, which isn't
fuel, it seems. Believe it or not, that's a good thing G

R.

It is leaking at rest. When not running I keep it locked in the up
position and out of the water. When I put the motor down and into the
water I have found a small amount of oil comes out of a timy breather
hole in the upper case of the motor. I haven't had the motor in the
down position long enough to determine whether it also leaks when running.

My plan is to identify where the at-rest leak(s) is/are occuring, repair
it/them and then look for evidence of running leaks. It'll be slow, but
I know I'm making progress.
Thanks,
Mike

rhys wrote:

Interesting. Does it leak at rest or only when under load? What I am
getting at is does the rising engine heat cause a gasket somewhere to
fail, or is it the rising oil pressure that forces oil past a hole or
gasket or crack or something that "closes" or reseats itself when the
motor cools down?

I'm glad you are getting closer to the ultimate problem, which isn't
fuel, it seems. Believe it or not, that's a good thing G

R.