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4.
Air leaks:
If excessive air leaks into the intake ahead of the impeller, the jet unit will "slip". Possible sources of air leaks are
through a faulty gland seal, which is usually accompanied by a static water leak into the boat when standing idle.
So if the gland is worn out and leaking into the boat with the engine off, it can also suck air when accelerating on to plane, and
if this happens, then the thrust is reduced dramatically. Air can also be introduced into the system via the inspection cover, so
you will want to make sure the cover is tight.
C. Low RPM = engine problem
There is generally no way the jet unit can overload the engine and bring the RPM's down. If the RPM's are down
from usual, it is almost certain to be an engine problem. A compression check will usually reveal leaking piston rings or valves,
but the most common reasons for reduced engine power are:
1.
Throttle:
Check that the throttle is opening fully.
2.
Fuel:
The fuel supply must be adequate for the engine size. Racing boats frequently have a fuel pressure gauge which is,
with the tachometer, probably the most important engine instrument. Sufficient fuel must be reaching the engine.
3.
Air to the engine:
The carburetor must be getting its full quota of cool air. If the engine has to work to get adequate air, and if
it is hot air, this will reduce power.
4.
Ignition spark:
Be satisfied the ignition system is operating properly. A problem here is usually indicated by a rough running
or missing engine.
5.
Exhaust:
Check for a free flowing exhaust system. Some silencers can become blocked, rubber hoses disintegrate inter-
nally, or there is excessive water injection. Such things can cause excessive back pressure and reduce power.
Provided your engine is getting its full quota of air and fuel, and is getting enough spark and at the right time, the en-
gine will usually be OK, and maximum RPM's will result. However if the RPM's are down and you believe the tachometer, look
for an engine problem. The hull, engine, and jet unit are the three main areas to look at when your performance is down.
