5000 - 8000 RPM Surprise
 

I was cruising along in my 24ft pontoon boat when I got a real surprise.
Somebody please tell me how and why I could be running wide open throttle at
my normal 5500 rpm and then suddenly the boat took off like a bat out of
hell running at 8000 rpms and 25mph??? I never touched the throttle. It
has never run that fast ever. After about 2 minutes it went back down to
5500 and never did 8000 again. Its a 60hp mercury Bigfoot outboard. It has
never done this before and I don't even know how it could rev that high and
go 25mph. Normal is 5500 and 17mph. What happened??

Mike

5000 - 8000 RPM Surprise
 

"Mike Slater" wrote in message
news:knfZl.742458$yE1.158636@attbi_s21...
I was cruising along in my 24ft pontoon boat when I got a real surprise.
Somebody please tell me how and why I could be running wide open throttle
at my normal 5500 rpm and then suddenly the boat took off like a bat out of
hell running at 8000 rpms and 25mph??? I never touched the throttle. It
has never run that fast ever. After about 2 minutes it went back down to
5500 and never did 8000 again. Its a 60hp mercury Bigfoot outboard. It
has never done this before and I don't even know how it could rev that high
and go 25mph. Normal is 5500 and 17mph. What happened??

Mike


Is it a two stroke? I've often noticed on 2 stroke weed wackers or chain
saws that just as you are about to run out of fuel they speed up. I think
they start running lean due to air in the fuel line.
Is it possible you had a temporary air leak in a line and a similar thing is
happening?

Eisboch

5000 - 8000 RPM Surprise
 

Eisboch wrote:
"Mike Slater" wrote in message
news:knfZl.742458$yE1.158636@attbi_s21...
I was cruising along in my 24ft pontoon boat when I got a real surprise.
Somebody please tell me how and why I could be running wide open throttle
at my normal 5500 rpm and then suddenly the boat took off like a bat out of
hell running at 8000 rpms and 25mph??? I never touched the throttle. It
has never run that fast ever. After about 2 minutes it went back down to
5500 and never did 8000 again. Its a 60hp mercury Bigfoot outboard. It
has never done this before and I don't even know how it could rev that high
and go 25mph. Normal is 5500 and 17mph. What happened??

Mike


Is it a two stroke? I've often noticed on 2 stroke weed wackers or chain
saws that just as you are about to run out of fuel they speed up. I think
they start running lean due to air in the fuel line.
Is it possible you had a temporary air leak in a line and a similar thing is
happening?

Eisboch



For two minutes? I can't believe 8000 rpms didn't blow it up!

5000 - 8000 RPM Surprise
 

Your prop hub is slipping. Get the prop rebuilt.
JR
BTDT got the T-shirt, too

Mike Slater wrote:

I was cruising along in my 24ft pontoon boat when I got a real surprise.
Somebody please tell me how and why I could be running wide open
throttle at my normal 5500 rpm and then suddenly the boat took off like
a bat out of hell running at 8000 rpms and 25mph??? I never touched the
throttle. It has never run that fast ever. After about 2 minutes it
went back down to 5500 and never did 8000 again. Its a 60hp mercury
Bigfoot outboard. It has never done this before and I don't even know
how it could rev that high and go 25mph. Normal is 5500 and 17mph.
What happened??

Mike

--
--------------------------------------------------------------
Home Page: http://www.seanet.com/~jasonrnorth

5000 - 8000 RPM Surprise
 

"Eisboch" wrote in message
...

"Mike Slater" wrote in message
news:knfZl.742458$yE1.158636@attbi_s21...
I was cruising along in my 24ft pontoon boat when I got a real surprise.
Somebody please tell me how and why I could be running wide open throttle
at my normal 5500 rpm and then suddenly the boat took off like a bat out
of hell running at 8000 rpms and 25mph??? I never touched the throttle.
It has never run that fast ever. After about 2 minutes it went back down
to 5500 and never did 8000 again. Its a 60hp mercury Bigfoot outboard.
It has never done this before and I don't even know how it could rev that
high and go 25mph. Normal is 5500 and 17mph. What happened??

Mike


Is it a two stroke? I've often noticed on 2 stroke weed wackers or chain
saws that just as you are about to run out of fuel they speed up. I think
they start running lean due to air in the fuel line.
Is it possible you had a temporary air leak in a line and a similar thing
is happening?

Eisboch


Yep. Its a two-stroke. It really caught me by surprise. Next time I will
look at the clear inline gas filter down near the primer bulb to see if its
empty if and when it happens. It was only my second outing this year so who
knows what going on and was too shocked to think about looking at the fuel
situation. You know, it sounded great at 8000 revs.

5000 - 8000 RPM Surprise
 

"JR North" wrote in message
diainc...
Your prop hub is slipping. Get the prop rebuilt.
JR
BTDT got the T-shirt, too

Mike Slater wrote:

I was cruising along in my 24ft pontoon boat when I got a real surprise.
Somebody please tell me how and why I could be running wide open throttle
at my normal 5500 rpm and then suddenly the boat took off like a bat out
of hell running at 8000 rpms and 25mph??? I never touched the throttle.
It has never run that fast ever. After about 2 minutes it went back down
to 5500 and never did 8000 again. Its a 60hp mercury Bigfoot outboard.
It has never done this before and I don't even know how it could rev that
high and go 25mph. Normal is 5500 and 17mph. What happened??

Mike


Nope. The boat went from its normal 17mph WOT cruising speed up to 25mph in
an instant.

Mike

5000 - 8000 RPM Surprise
 

NO WAY is the prop hub slipping. That would be 8000 rpms and ducks
swimming by you.
I vote for leaning out. BIG bubble in the fuel line, or the kid hooked
up a nitro bottle!
Den
48YF EAGLE

Nope. *The boat went from its normal 17mph WOT cruising speed up to 25mph in
an instant.

Mike

5000 - 8000 RPM Surprise
 

Mike Slater wrote:

"Eisboch" wrote in message
...

"Mike Slater" wrote in message
news:knfZl.742458$yE1.158636@attbi_s21...
I was cruising along in my 24ft pontoon boat when I got a real
surprise. Somebody please tell me how and why I could be running wide
open throttle at my normal 5500 rpm and then suddenly the boat took
off like a bat out of hell running at 8000 rpms and 25mph??? I never
touched the throttle. It has never run that fast ever. After about 2
minutes it went back down to 5500 and never did 8000 again. Its a
60hp mercury Bigfoot outboard. It has never done this before and I
don't even know how it could rev that high and go 25mph. Normal is
5500 and 17mph. What happened??

Mike


Is it a two stroke? I've often noticed on 2 stroke weed wackers or
chain saws that just as you are about to run out of fuel they speed
up. I think they start running lean due to air in the fuel line.
Is it possible you had a temporary air leak in a line and a similar
thing is happening?

Eisboch


Yep. Its a two-stroke. It really caught me by surprise. Next time I
will look at the clear inline gas filter down near the primer bulb to
see if its empty if and when it happens. It was only my second outing
this year so who knows what going on and was too shocked to think about
looking at the fuel situation. You know, it sounded great at 8000 revs.

Mike,
You may want to consider dropping back to a "cruising" rpm, instead of
running it WOT. Running the boat at WOT will shorten the life of the
engine considerably and use about 3 times the gas. For most boats, the
best gph or mpg is about 3400-3600 rpm. You shouldn't pick up much
incremental speed at WOT.

--
Reginald P. Smithers III, Esq.

This Newsgroup post is a natural product. The slight variations in
spelling and grammar enhance its individual character and beauty and in
no way are to be considered flaws or defects

5000 - 8000 RPM Surprise
 

Reginald P Smithers III, Esq. wrote:
Mike Slater wrote:

"Eisboch" wrote in message
...

"Mike Slater" wrote in message
news:knfZl.742458$yE1.158636@attbi_s21...
I was cruising along in my 24ft pontoon boat when I got a real
surprise. Somebody please tell me how and why I could be running
wide open throttle at my normal 5500 rpm and then suddenly the boat
took off like a bat out of hell running at 8000 rpms and 25mph??? I
never touched the throttle. It has never run that fast ever. After
about 2 minutes it went back down to 5500 and never did 8000 again.
Its a 60hp mercury Bigfoot outboard. It has never done this before
and I don't even know how it could rev that high and go 25mph.
Normal is 5500 and 17mph. What happened??

Mike


Is it a two stroke? I've often noticed on 2 stroke weed wackers or
chain saws that just as you are about to run out of fuel they speed
up. I think they start running lean due to air in the fuel line.
Is it possible you had a temporary air leak in a line and a similar
thing is happening?

Eisboch


Yep. Its a two-stroke. It really caught me by surprise. Next time I
will look at the clear inline gas filter down near the primer bulb to
see if its empty if and when it happens. It was only my second outing
this year so who knows what going on and was too shocked to think
about looking at the fuel situation. You know, it sounded great at
8000 revs.

Mike,
You may want to consider dropping back to a "cruising" rpm, instead of
running it WOT. Running the boat at WOT will shorten the life of the
engine considerably and use about 3 times the gas. For most boats, the
best gph or mpg is about 3400-3600 rpm. You shouldn't pick up much
incremental speed at WOT.

Excellent advice especially if it is an older motor drawing it's last
breaths.

5000 - 8000 RPM Surprise
 

On Mon, 15 Jun 2009 02:27:29 -0700 (PDT), den wrote:

NO WAY is the prop hub slipping. That would be 8000 rpms and ducks
swimming by you.
I vote for leaning out. BIG bubble in the fuel line, or the kid hooked
up a nitro bottle!
Den
48YF EAGLE

Nope. *The boat went from its normal 17mph WOT cruising speed up to 25mph in
an instant.

Very interesting. Unusual motor to say the least. Power required to
overcome viscous drag varies with the cube of the speed. So this
engine tripled the power while going from five grand to eight. All you
can get from nitrous oxide is double. If you supercharge and burn
methanol, in an engine designed for it, you might triple the power
going from five to eight.

It is would be more usual for power to drop going five grand to eight.
Matter of insufficient time for the cylinders to get a full charge of
air.

Casady