Yamaha T8 Rigging Manual page 91

Outboard Rigging Guide - 2001
Trim
On some applications, your boat may tend to pull
to starboard. This condition can easily be correct-
ed by bending the trailing edge of the flow-
straightening fins. The fins are located at the top
and bottom of the exhaust tube 1/16" toward the
starboard side of the motor.
Idle
In most cases, the stock idle adjustments will pro-
duce an acceptable neutral. However, since neu-
tral is a balance between forward and reverse
forces, some slight creeping of the boat may occur
at idle. A minor idle-speed adjustment should cor-
rect this tendency.
Performance Tips
Here are some pointers for obtaining maximum
performance from jetdrive outboards:
1. Keep the leading edges of the impeller sharp.
Edges that have been blunted by gravel
(beyond 1/32-inch) tend to break up the
water. This results in slippage and engine
overspeeding.
2. Keep the grille bars parallel to prevent large
rocks or other debris from entering the
impeller, causing damage or possible lodging
in the nozzle.
3. Select as light a hull as possible for the
intended use.
4. Keep the boat bottom smooth and free of
Jet Drive Eng. Mtg., Maintenance,
Shift Cable Instruction, Service Info.
dents. This will reduce drag and air entrap-
ment.
5. The optimum bottom width is 48 to 60 inch-
es. Beyond 60 inches, the boat rides so high
that air is allowed to enter the pump. This is
likely in choppy water particularly when run-
ning with the wind. Less than 48 inches, on
the other hand, can make it difficult to reach
planing with a heavy load.
6. A slight vee in the boat bottom gives better
steering and helps to keep solid water in the
pump. A 3-inch drop at centerline on a 60-
inch bottom is enough. Beyond that, shallow
draft is sacrificed.
7. The power trim is useful to bring a heavy
load on plane. Tipping the engine under
points the jet stream down, which helps lift
the stern. After reaching a plane, trim the
engine out until the jet stream is horizontal
(the engine driveshaft is vertical).
CAUTION:
Do not trim the engine out beyond horizontal,
so the jet stream points up into the air or the
bow lifts. This will reduce the ram angle on the
water intake and will cause severe cavitation
burns on the impeller blades.
Power trim is also useful when running slow-
ly in shallow water, such as when backing off
the beach. In these circumstances, the engine
can be tilted back 15 to 20 degrees, reducing
the tendency to pick up gravel. Keep your eye
on the cooling water pilot hole to make sure
the engine is getting water.
8. Stainless steel impellers are available. They
give extended life in areas where it is difficult
to avoid gravel intake.
A 4-blade stainless steel impeller is also
available. On the high horsepower motors,
particularly the V-6s, it gives better accelera-
tion (less slippage and engine overspeed),
and enables picking up heavier loads.
2-28