Yamaha 9.9 outboard runs smooth then sputters

[m***@sbcglobal.net]

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

[Chris Newport]

On Tuesday 20 July 2004 8:19 pm in rec.boats.cruising

Post by m***@sbcglobal.net
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.

Sounds like a blocked tank breather to me.
On small outboards the breather is often a small hole in the fuel filler
cap. If this is blocked or if you have the wrong fuel cap there will be
a vacuum in the tank as fuel is pumped out into the engine.
The simple test for this is to loosen the filler cap.
Some tanks have a finger screw on the cap which you need to open when
running the engine.

[Esourcedesigns]

Sounds like a weak fuel pump or a sticking needle and seat in the carb.

Dennis

Post by m***@sbcglobal.net
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

[sherwindu]

Another possibility is bad gas, being either old or contaminated. Try a
fresh tank.

Sherwin Dubren

Post by m***@sbcglobal.net
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

[m***@sbcglobal.net]

Thanks everyone! The gas was new last weekend, so I don't think that's
the problem. I'll check the other things when I get back into town
tomorrow.
Thanks again,
Mike

Post by m***@sbcglobal.net
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

[Leanne]

Post by m***@sbcglobal.net
Thanks everyone! The gas was new last weekend, so I don't think that's
the problem. I'll check the other things when I get back into town
tomorrow.
Thanks again,

Mike,
When you speed up the motor, does applying a little choke let it go to
higher RPM's? I had this problem a couple times as the motor sits on the
pushpit most of the time and what is left in the carburator gums it up. I
always turn the gas off and run it till it quits, but after a few months the
problem is back again.

Leanne

[m***@sbcglobal.net]

Leanna,
I thought of using the choke too, and tried it last night. It didn't do
any good. But it could be that the carb is gummed up. I'll add that to
my list of things to check.
Thanks!

Post by Leanne

Post by m***@sbcglobal.net
Thanks everyone! The gas was new last weekend, so I don't think that's
the problem. I'll check the other things when I get back into town
tomorrow.
Thanks again,

Mike,
When you speed up the motor, does applying a little choke let it go to
higher RPM's? I had this problem a couple times as the motor sits on the
pushpit most of the time and what is left in the carburator gums it up. I
always turn the gas off and run it till it quits, but after a few months the
problem is back again.
Leanne

[rhys]

Post by m***@sbcglobal.net
Thanks everyone! The gas was new last weekend, so I don't think that's
the problem. I'll check the other things when I get back into town
tomorrow.
Thanks again,
Mike

Another possibility which happened to my four-stroke Honda 9.9 is a
stuck carb float, which make for harder starts, limited acceleration
and the occasional stall. It needed a good clean due to crap in the
gas.

Filtering the gas/cleaning the tank is always a good idea.

R.

[Michael]

Factory prop or did you change it for one with a different pitch?

Post by rhys

Post by m***@sbcglobal.net
Thanks everyone! The gas was new last weekend, so I don't think that's
the problem. I'll check the other things when I get back into town
tomorrow.
Thanks again,
Mike

Another possibility which happened to my four-stroke Honda 9.9 is a
stuck carb float, which make for harder starts, limited acceleration
and the occasional stall. It needed a good clean due to crap in the
gas.
Filtering the gas/cleaning the tank is always a good idea.
R.

[Mike_H]

I replaced the factory prop with a plastic one of the same pitch.
Mike

Post by Michael
Factory prop or did you change it for one with a different pitch?

Post by rhys

Post by m***@sbcglobal.net
Thanks everyone! The gas was new last weekend, so I don't think that's
the problem. I'll check the other things when I get back into town
tomorrow.
Thanks again,
Mike

Another possibility which happened to my four-stroke Honda 9.9 is a
stuck carb float, which make for harder starts, limited acceleration
and the occasional stall. It needed a good clean due to crap in the
gas.
Filtering the gas/cleaning the tank is always a good idea.
R.

[Tom R.]

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

Post by m***@sbcglobal.net
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

[Dave]

Post by m***@sbcglobal.net
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.

Could be a partially blocked jet in the carb.

[m***@sbcglobal.net]

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

Post by m***@sbcglobal.net
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

[rhys]

Post by m***@sbcglobal.net
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.

[Mike_H]

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

Post by rhys

Post by m***@sbcglobal.net
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.

[rhys]

Post by Mike_H
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.

[Mike_H]

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

Post by rhys
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.