Yamaha F100 Prime Start

[Tirill11]

Can anyone explain the Prime Start system on my Yamaha F100, 2001 model. (Yes, it is carburators)

Is the 12V voltage on all the time to the Prime starter assembly valves, or is it switching off after a certain time or the motor has achieved an certain temperature??

Above seem to be impossible to read out from my service manual.

[99yam40]

Not sure about your F100, but most other Prime Start systems I have seen have voltage on the electrothermal valves as long as motor is running.

In other words the voltage comes directly from rectifier/regulator only when motor runs, that heats up a wax pellet inside the valve that expands pushing needle down into its seat and closes off passages stopping flow of enriched fuel.

[Tirill11]

But how cab U check these valves? I guess the first thing is to check that they get voltage, and actually gets WARM, but is there anyway to check that they really move the needle.
Can U see or measure the movement in some way if U lift up the device????

[99yam40]

Yes, the procedure should be in the service manual along with the spec

[Tirill11]

I have only the Clymer Manual, and I can say it is very "thin" coverd there. No specs and no procedure whatsoever. I have heard that some measurements can be taken on hot and cold wax actuator, but never seen these figures. Anybody...?

[Sequoiha]

take the valve out and lay it on a table, set the point about an 1/8 of an inch from something,,, apply 12v dc and a ground, the needle should extend about 3/32 of an inch, if this occurs the prime start valve is ok.. the voltage comes from the charge coil, and the wax pellet heats up and expands from this voltage and the heat of the engine. when the engine cools off and the voltage is no longer applied the was pellet contracts and opens the fuel flow for a cold start..