On Mon, 11 Jul 2005 04:00:04 GMT, Peggie Hall
wrote:

Kevin Jed wrote:

I have a Mercruiser 120 fuel problem. There is a small tube going from the
fuel pump to the throat of the carburetor (like a vacuum tube) and it is
injecting a large volume of fuel into the carburetor throat, bypassing the
float assembly altogether and flooding the engine. When I remove this tube
and attempt to plug it, the engine runs properly but there is so much
pressure on this little tube it blows the plug out and starts pouring raw
fuel into the boat! Automotive engines don't have this tube, and I don't
know what it's purpose is. Can anyone offer any help? Thanks!

This is a bit out of my area of professional expertise, but I've had
experience (that included a VERY expensive lesson!) with mechanical fuel
pumps on my own Mercruiser and Chrysler engines...I know just enough
about this to be dangerous.

Inboard marine engines are designed to dump fuel into the oil crankcase
if the diaphragm fails...that's a safety measure, to keep gas--and
especially gas fumes--out of the bilge. That line--which is called a
"sight tube" and SHOULD be clear hose (although it's entirely possible
that someone who knew even less than you do replaced it with black hose)
that lets you see whether anything is going through it. If it's
squirting gas, I'd bet real money that the diaphragm HAS failed. The
lifespan of most diaphragms is only about 5-7 years...if the boat has
sat unused for any length of time, it can be even shorter, 'cuz the
diaphragm can dry out and split when the boat is fired up again. So I
THINK you need a new fuel pump. Fortunately, manual fuel pumps are a lot
less expensive than electric fuel pumps.

But, as I said above, I know just about enough about engines to be
dangerous. So before you do anything--especially before you run the boat
again, get the manual for the engine so you'll not only know how to
install a marine fuel pump correctly, but the rest of what you need to
know about the difference between that engine and its automotive
counterpart. And also talk to a certified Mercruiser mechanic...'cuz you
can get all kinds WAG advice here...but HE'LL have the RIGHT advice.


This post of Peggie's hit the jackpot, for me. It was insightful
(about not letting gasoline dribble) and confirmed for me what the OP
finally concluded_ a neat gas feed into a carburettor is a very very
bad thing!

Choking has a place, but over rich fuel does an engine a power of no
good. I am coming to the conclusion thjat a prime reason that modern
engines with computer fuel control, timing etc. last so much longer
than back in the day, is that the gas/air mix is always optimal to
lean - which works well if pinging is also avoided.

Brian Whatcott Altus OK