[C320-list] Throttle and Tachometer

[Sean Kaldor]

Seems like two separate issues... Since you are hull #1035, I'm not sure if you are a Yanmar 3GM30F or 3YM30.

Tachometer
The 3GM30F has a sensor on the flywheel that counts the teeth as they pass. This sensor is connected by two wires to the tach. If the tach is jumping around, *and there is no change in engine noise and the motor isn't speeding up/slowing down* it is either a faulty/blocked sensor, bad wire connection at the sensor, faulty wiring, bad wire connection at the tach, corroded tach calibration setting, or faulty tach.
I have heard that the wire connection at the sensor fails frequently, and simply unplugging, cleaning, and reattaching will fix the issue. This usually causes a jumping/erratic tach.
Mine went wrong, and it turned out that the calibration/setting screw on the back of the tach had some corrosion on it. By simply turning it back and forth a few times, and returning it to its original setting, everything was fine. My symptom was a tach reading steady, but 500-900 RPM too high.
A photo tachometer is an excellent tool to calibrate the tach and verify it speed. About $28 from Amazon, or free (w/shipping) through the C320 tool cache.
I *think* the 3YM30 uses an alternator based tachometer. Can't help you there.

Throttle
The throttle is a mechanical cable that runs from the pedestal lever, through a resistance setting screw, through a mount, down to the engine (forward starboard side of 3GM30F) where it is connected to the actual throttle control and a set screw controls the idle speed.
Pushing the lever all the way forward (max throttle) pulls the cable away from the engine, pulling the throttle control aft.
You need to figure out if the cable is slipping (or has slipped, or is blocked) at the motor throttle connection, or at the pedestal lever connection. If neither of those have slipped or are blocked, then there is an issue that is preventing the motor from gaining RPM... a more complicated issue.
The big question is what do you mean by "the throttle will not move foward as it should and I can not run the engine wide open". If you mean that the pedestal throttle lever physically hits some kind of hard stop before reaching full throttle, then I would investigate:
    1) Cable connection at the pedestal lever (remove the compass cover, or possibly the compass too, and look inside)
    2) Cable connection at the motor throttle control
making sure there is full range of motion without blockage or slippage. With the pedestal throttle all the way aft, the motor throttle should be all the way forward, pressed against the idle set screw.

That's all I've got!

Sean
#499 Liberte
San Francisco


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Message: 6
Date: Sat, 20 Mar 2010 15:50:31 +0000
From: "Kurt Budelmann" <krbmd77 at charter.net>
To: "Catalina320.org" <C320-List at Catalina320.com>
Subject: [C320-list] Throttle and Tachometer
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Help!  All of a sudden the throttle will not move forward as far as it should and I can not run the engine wide open. Also the tachometer is reading higher than it used to and the needle is jumping around. Is this a cable problem?
Kurt