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I
have a 41-footer with twin gasoline stern drives. Lately I’ve noticed
decreased engine power and surging at higher speeds on one engine. Everything
seems to check out, but the problem reoccurs. Any suggestions? T.B.,
via e-mail
Assuming you
have twin fuel tanks and that only one engine is drawing from one tank,
look at the fuel tank vent serving the misbehaving engine. Proper venting
is required for fuel to flow from the tank to the engine, and if there
is even a small obstruction in the vent, the fuel pump may not be able
to pull enough fuel from the tank to supply the engine, especially at
higher speeds. The result can be decreased power or surging and, if the
restriction is considerable, stalling at lower speeds or even failure
to start.
A typical
vent system for an integral fuel tank, as illustrated here, includes a
hose that leads from the top of the tank to a fitting mounted on the outside
of the hull. Having a small orifice, this fitting is notoriously prone
to blockage by debris, especially insect nests.
To determine
if this is the source of your problem, loosen the fill cap enough to allow
the tank to vent, and then run the engine. If all appears to be normal,
a clogged vent is most likely the culprit. To clear the obstruction, remove
the hose from the vent and push any debris through to the outside. Failure
to do so can cause the debris to be sucked into the fuel tank and, eventually,
into your engine, causing more problems.
During
a recent tune-up on my tender’s two-stroke outboard, I noticed a
deposit wedged between the electrode and the spark plug electrode. What
can be causing this? P.G., via e-mail
This condition
is known as core bridging and is caused by excessive carbon adhering to
the electrode. Possible causes include the use of improper oil, immediate
high-speed operation after prolonged trolling, and an improper fuel-oil
ratio.
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