Tachs operate from a signal from the ignition system. It is not a varying
voltage, it is a varying frequency tied to the ignition firing. You can't
easily test with regular test equipment. A scope would tell you. If both
tachs went at the same time thne I'd suspect supply and ground connections.
Did you measure the voltage with the wires connected to the tach? An open
wire sometimes will read the correct voltage because it has no load. If
they did not fail at the same time you should have swapped tachs and then
ignition modules when the first one went to determine if it is the tach, the
ignition module, or the wiring.

Most sending units are a varying voltage to the gauge. You should be able
to move the sending unit arm and measure different resistances with an ohm
meter. Some yamaha sending units are a series of magnetic switches but they
still have different resistances depending on how many of the little floats
are raised.

Sounds like you have a linkage problem. Somewhere along the way the
throttle cable from the front has to actuate connections to both engines.
This is where your problem is.

wrote in message
oups.com...
I have an '01 Yamaha jetboat. Everything works well except neither tach
will operate, the oil level indicator says its empty (when its full),
and one of the throttles has to be held in position by hand or it will
fall back to idle.

I purchased a service manual and its terrible. There are no voltages
listed even for the tachs - I'd expect the schematic to say something
like 0-6000 RPM ~ 0-12V and point to a wire?

Since neither tach operates I sort of suspected a "common" wire but
ground and 12v seem to be present.

I replaced the oil tank level sending unit, didn't help. It comes on
and audibly alarms after like 10 seconds of operation.

Also the throttle assemply- they show an exploded diagram and that's
it. No adjustments. What do I need to adjust to tension the throttle so
it stays in postion?

Any advice would be appreciated. Well except for GET RID OF THAT BOAT!!
Any HELPFUL advice

I managed to get the service port covers out; they were terribly stuck
(bought it like that).. It took a 2 ton engine lift to do it- lift the
whole boat off the trailer almost! If you have one of these boats I
advise you to remove these and leave them off unless you're ready to
trailer it. Then apply lube according to the manual.


Spy