|
I’ve
got a 90-hp two-stroke outboard that I am told might have a problem with
its fuel-bleed recirculation system. Can you explain how this works and
what can happen if it fails? B.A., via e-mail
This system
is designed to collect fuel and oil from the low spots of the individual
crankcase areas, since two-stroke intake systems do not completely transfer
all of the fuel sent through the crankcase to the combustion chamber.
This is especially important during low-speed operation. The bleed system
pumps the fuel/oil to the intake ports or intake manifold, where it is
transferred to the combustion chamber and burned.
Many
recirculation systems also collect the fuel and oil pooled in the lower
crankcase bearing area and pump it to the upper crankcase bearing to ensure
proper lubrication in this location. If this type of system fails, the
engine can suffer an upper crankcase bearing failure. Regardless of the
type of system, excessive fuel and oil will puddle in the crankcase and
not reach the combustion chamber during low-speed operation, causing a
lean mixture. When the engine accelerates, the puddles will be quickly
drawn into the engine, causing a temporary rich mixture that will result
in poor low-speed performance, poor acceleration, spark plug fouling,
stalling or spitting at idle, and excessive smoke on acceleration.
What
is the difference between intercooling and aftercooling? S.C.,
via e-mail
In modern
engines, none. In some older two-stroke Detroit Diesels, the intercooler
was located between the intake manifold and the blower, where the aftercooler
was beneath (downstream of) the blower. In all other engines the terms
are used interchangeably and refer to the process of cooling the engine
intake air after it leaves the turbocharger but before it enters the cylinders.
Because it allows more air to enter the cylinders, aftercooling/intercooling
increases power and fuel efficiency and lowers NO2 emissions.
Need
help with a maintenance problem? Write to Maintenance Q & A, Power
& Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax:
(917) 256-2282. e-mail:ken_kreisler@primediamags.com.
No phone calls, please.
Next page
> Exhaust Bellows, and more > Page 1,
2
|