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

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.


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