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backfire is
extremely critical for safe boat operation, but if your arrestor limits the air flow to
your engine, it is, in effect, "throttling" your engine's power. As a rule of
thumb, the following chart is offered to determine if your flame arrestor is too
restrictive and a large arrestor should be considered.
Engine Maximum manifold vacuum
displacement without "throttling"
300 1.0"
350 11/2"
454 2"
502 2"
To select a "larger" flame arrestor, begin by determining the "effective
area" of your existing arrestor. To do this, measure the outside diameter (d) of the
element and the height (h) of the element between the base and cover. Then. apply this
formula:
Effective Area = 3.14 x d x h IN2
To select a new arrestor, choose one which has an effective area at least 25%
greater than the area of your standard arrestor. Remember, if clearance over the top of
the arrestor is a problem, by choosing an arrestor with the same height but a larger
diameter, you will increase the effective area without problem.
A special note here for those who intend to operate their vessels at or near wide open
throttle for extended periods of time. You cannot have a flame arrestor too large.
Crankcase fumes during wide open operation carry considerable oil in the fumes, and flame
arrestor air flow reduction occurs as the elements are coated with oil. For the sake of
maximizing power, use the larger arrestor for these high performance cases.
E. Propeller Limitations on Wide Open Throttle Performance
The propeller, as discussed earlier, transfers a load to the engine which effectively
limits wide open throttle engine speed. Smaller diameter propellers turn faster than
larger diameter propellers if both are of equal pitches. Changing to a propeller of a high
pitch will slow the wide open throttle engine speed down. If you feel your engine needs to
turn faster to increase your performance see your marine dealer for a propeller selection
suggestion.
Earlier, it was mentioned that vibration is on indicator of propeller damage. Not
all damage to propellers can be seen by the naked eye. Propeller blades can be sprung,
and, therefore, require balancing by a responsible prop shop It is not wise to run an
engine if propeller vibration is evident. Damage to outdrive bearings and shaft struts can
occur rapidly and with disastrous results. Propellers should be reconditioned each year no
matter if the encounter with underwater obstruction was severe or not.
F: Importance of Vessel Trim and Hull Condition
One trip to a boat yard in the spring reveals a good review of vessel trim and hull
conditions. Good hydraulic trim tabs allow the boat operator to adjust the boat attitude
for onboard loading as well as water conditions. It can be argued that proper loading
stowage ca n aid in vessel trim, but wind and wave action can not be compensated without
tabs. Wise owners of outdrive boats also install tabs as stern downward forces by the trim
tabs are more effective in boat trim than changing the angle of thrust on the outdrive.
Since tabs come in pairs. six degrees of adjustment are possible for all round boat trim.
Hull condition for maximum wide-open throttle performance means underwater surface
condition and preparation. All marine growth must be eliminated to reduce drag. and
scratches or hull nicks should be removed. The smother the hull is, the less drag is
present, and the less horsepower is lost to the water.
HOW TO CARE FOR YOUR MARINE CARBURETOR FOR BEST PERFORMANCE
A. Corrosion Protection
Corrosion protection is more than just for looks. Exterior corrosion can affect the
function of your carburetor. Holley marine carburetors come polished to a high luster to
complement the dress items on today's marine engine. A few easy steps can keep your
carburetor looking good and functioning properly. To keep your carburetor bright, protect
the exterior surface finish by applying a clear acrylic spray which can be found in most
art and craft stores.
Exterior springs on the throttle shafts and the idle speed and mixture screws can
be protected by wiping them with a cloth which has been sprayed with a light oil such as
WD. 40. Do not spray the oil on the springs as too much oil will attract dust and dirt
which will later cause spring binding. In some cases, during salt water operation,
airborne salt sprays find their way on to the carburetor. When this happens, only
immediately rinsing with fresh water can stop the eventual corrosion. A point of interest
is that the Holley marine carburetor rebuild kit will include replacement springs for
these applications.
B. General Service
To insure proper service from a marine carburetor, the best advice is to keep it clean and
free from corrosion. Keeping it clean means the outside should be inspected for residue
from flame arrestor tube connections. Some manufacturers route the fumes from the valve
covers to the element of the arrestor. Oil fumes condense and drip down on the carburetor
where they attract dirt, or worse, cause caustic attack on the carburetor surfaces.
Other engine manufacturers vent the valve covers through a breather which vents the
flow by products to carburetor area. The natural air flow to the flame arrestor keeps
these vapors airborne where they finally settle on the carburetor. The exterior of the
carburetor should be wiped clean to prevent residue build up. At the same time, the flame
arrestor should be inspected and cleaned thoroughly with a good cleaner. Linkage on
the carburetor should be cleaned to retain proper carburetor operation. The only area that
lubrication should be used is on the throttle cable and the throttle ball to which it
attaches. Use no other lubricants on carburetor moving parts.
Rubber parts such as hoses, gaskets, pump diaphragms and secondary diaphragms.
should receive periodic inspection as these parts are attacked by ozone and deteriorate at
high temperatures. Any hose which exhibits any surface cracking when bent 90o,
should be replaced. Carburetor gaskets which weep fuel, as evidenced by stains on the
casting surfaces, should be replaced. Pump diaphragms should be inspected regularly
because during lay-up periods, the most detrimental materials in the fuel are in close
contact with the accelerator pump diaphragm.
Holley has engineered very specific rebuilding kits for nearly all marine carburetors, and
these kits are a good source of parts needed for regular maintenance.
C. Fuel Additives and Storage Fuel Stabilizers
The fuel tank of a marine vessel exists in an atmosphere of nearly 100% humidity for the
life of the vessel. This means that during temperature excursions of a normal summer day,
the fuel tank sees condensation of water in the fuel tank. This water being heavier (more
dense) than the fuel settles to the fuel tank bottom where it accumulates. When the level
of water reaches the bottom of the fuel pick-up tube, it proceeds through the system to
the carburetor. Some fuel systems have water separators, but often these are not regularly
serviced and water still finds its way to the carburetor fuel bowl. Water in the fuel bowl
of any carburetor means real trouble. Corrosion of metering components often means
expensive carburetor repair. Water in the combustion chamber means erratic idle, stalling,
with loss of vessel control, and loss of power at cruise.
The best solution for these problems is to keep the fuel tank from having space in
which moisture-laden air can collect and drop its water into the tank. If the fuel tank is
kept full of fuel, this air can not collect, and therefore, most water is eliminated. Use
of additives, which are usually methanol alcohol with a drop or two of isopropyl alcohol
to "dry out" the fuel, only aggravates corrosion problems. Plus, these alcohol
water mixtures also create problems with the rubber components and pump diaphragms. The
answer to solving water problems is simple: keep your fuel tank(s) full, and replace your
fuel /water separator regularly.
During winter lay up, most storage yards request that fuel tanks be filled to
prevent excessive fuel vapors The fuel in these tanks should be treated with a fuel
stabilizer to prevent the fuel from going "sour". "Sour gas" is the
most damaging substance a fuel system can encounter. Fuel stabilizers should be used in
concentrations according to the manufacturer's instructions.
D. Lay Up and Fitting Out
In preparation for winter lay up the carburetor should be cleaned externally and
drained of all fuel by the following procedure. When lay up is imminent, and while the
boat is still in the water, run the engine with transmission in neutral at about 1,000
RPM, Open access hatch and locate the fuel line shut off valve. Have ready a spray can of
engine fogging oil. Remove flame arrestor while engine is at fast idle (1,000 RPM) and
shut off fuel line valve. Position spray oil can over primary carburetor and wait for
engine speed to change. An indication of running out of fuel will be an increase in idle
speed. As idle speed increases, begin spraying oil into the primary carburetor. Engine
speed will roughen, but it will not stall.
Continued spraying of the oil will allow all of the secondary carburetor fuel to be
expended. When this occurs, idle will roughen more. Cease spraying the oil and the engine
will stall. At this point. both fuel bowls are empty of all fuel except for a minimal
amount of unusable fuel below the main jets. This fuel should cause no problems since it
can not form varnish on any major metering restrictions. The excess oil which entered the
combustion chambers will lubricate and protect the rings, piston, etc. from corrosion
during lay up. Reinstall the flame arrestor, wipe off any spray which may be on the
outside of the carburetor. and cover the carburetor and flame arrestor with an old towel
or cloth. This will prevent those ever-inquisitive insects from building a winter home in
your flame arrestor. Further engine lay up and winterizing should follow manufacturer's
instructions.
(Continued on page 143)
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