Here is a scenario that might have happened to your boat.
Boat carburetors are designed to vent overflowing gas into their throats.
You may have observed some gas percolating in the intake manifold resulting
from an overheated engine. The overheat may have resulted from a plastic bag
being sucked against the water pickup in the lower unit. When you shut the
engine off the bag drifts away and no more overheating.
JIMinFL

"Melandre" wrote in message
...
I do a 20 minute boat run between the marina and my small cabin almost
every weekends. Something weird (and a bit scary) happened last
weekend. I warmed up the boat (idle) for about 5 minutes while
loading it and then we stated our usual run to the cabin. After about
5 minutes, my wife noticed a burnt smell and sure enough, when we
looked at the engine compartment, lots of smoke was coming out of it.
I have an older 18' Bayliner (1990) with an I/O OMC Cobra 2.3L
twin-cam engine. Because it is an I/O, I couldn't quite see inside
but my first reaction was that I may have a fire going in the engine
compartment (probably did!) . I promptly stopped and shut off the
boat and opened the engine compartment.

While I could not see an obvious fire, I suspected that gas overflowed
from the carb and spilled on the engine (would that be enough to
create all the smoke?). I unscrewed the flame arrestor (which was
very hot when normally it is not) and sure enough I could see gas (I
think) bubbling inside the carb (could a fire starts there???).

We were looking at a long paddle back to the marina and not knowing
much about boat mechanic (and therefore not having a clue what the
problem might be), I was a bit wary about even restarting the boat
(not wanting an explosion, a fire or blowing the engine). However,
the bubbling gas eventually dissipated so after 5-10 minutes, I
decided to give it a go (without the arrestor in place so I could
observe in there). The boat started and we started heading back
slowly toward the marina. Once I got in front of the marina,
everything looked OK (no more overflowing gas or burning smoke) so I
opened the throttle a little to do more testing. Everything OK again.
Put the flame arrestor back on and more testing. Again everything OK
and the flame arrestor was cool to the touch. After sufficient
testing, I concluded that things appeared to be back to normal, and
with the engine cover still off (so I could stop at any sign of
trouble), we turned around and proceeded to the cabin. 20 minutes
later we arrived at our cabin and again I checked around, touch the
flame arrestor and everything appeared normal. Use the boat a bit at
the cabin and again OK. Came back from the cabin last night to the
marina and no problem.

Otherwise the boat runs smoothly, no weird noise or other noticeable
problems.

So. what the heck happened! Even though the problem dissapeared as
quickly as it appeared, I am a bit freaked out that it will happen
again with perhaps more dire consequences next time. Any
suggestions, recommendations, advises or comments would be most
welcome.

Andre

On Tue, 21 Jun 2005 02:36:44 GMT, "JIMinFL" wrote:

Here is a scenario that might have happened to your boat.
Boat carburetors are designed to vent overflowing gas into their throats.
You may have observed some gas percolating in the intake manifold resulting
from an overheated engine. The overheat may have resulted from a plastic bag
being sucked against the water pickup in the lower unit. When you shut the
engine off the bag drifts away and no more overheating.
JIMinFL

"Melandre" wrote in message
.. .
I do a 20 minute boat run between the marina and my small cabin almost
every weekends. Something weird (and a bit scary) happened last
weekend. I warmed up the boat (idle) for about 5 minutes while
loading it and then we stated our usual run to the cabin. After about
5 minutes, my wife noticed a burnt smell and sure enough, when we
looked at the engine compartment, lots of smoke was coming out of it.
I have an older 18' Bayliner (1990) with an I/O OMC Cobra 2.3L
twin-cam engine. Because it is an I/O, I couldn't quite see inside
but my first reaction was that I may have a fire going in the engine
compartment (probably did!) . I promptly stopped and shut off the
boat and opened the engine compartment.

While I could not see an obvious fire, I suspected that gas overflowed
from the carb and spilled on the engine (would that be enough to
create all the smoke?). I unscrewed the flame arrestor (which was
very hot when normally it is not) and sure enough I could see gas (I
think) bubbling inside the carb (could a fire starts there???).

We were looking at a long paddle back to the marina and not knowing
much about boat mechanic (and therefore not having a clue what the
problem might be), I was a bit wary about even restarting the boat
(not wanting an explosion, a fire or blowing the engine). However,
the bubbling gas eventually dissipated so after 5-10 minutes, I
decided to give it a go (without the arrestor in place so I could
observe in there). The boat started and we started heading back
slowly toward the marina. Once I got in front of the marina,
everything looked OK (no more overflowing gas or burning smoke) so I
opened the throttle a little to do more testing. Everything OK again.
Put the flame arrestor back on and more testing. Again everything OK
and the flame arrestor was cool to the touch. After sufficient
testing, I concluded that things appeared to be back to normal, and
with the engine cover still off (so I could stop at any sign of
trouble), we turned around and proceeded to the cabin. 20 minutes
later we arrived at our cabin and again I checked around, touch the
flame arrestor and everything appeared normal. Use the boat a bit at
the cabin and again OK. Came back from the cabin last night to the
marina and no problem.

Otherwise the boat runs smoothly, no weird noise or other noticeable
problems.

So. what the heck happened! Even though the problem dissapeared as
quickly as it appeared, I am a bit freaked out that it will happen
again with perhaps more dire consequences next time. Any
suggestions, recommendations, advises or comments would be most
welcome.

Andre



This sounds reasonable. Check the rubber portions of the exhaust. If water
stopped going thru the exhaust, these may have gotten hot enough to start
smoldering. They put off a *lot* of smoke when they do. (Experience speaking
here!)
--
John H

"All decisions are the result of binary thinking."