Originally Posted by MikePz
Try this it worked for me on 3 different Yanmar
engines! The problem is the voltage loss in the starter solenoid circuit (wiring between the instrument panel and engine).
the problem with the installation
of a small starter relay in the circuit on newer engines. Addition of a homemade starter relay is very easy - let me know if you would like a diagram.
Yep, this is a common problem. The start wires in wiring
harnesses that connect the standard Yanmar instrument panel to the engine
wiring harness are too small, making the voltage drop to the solenoid too high for reliable starting.
Yammer offered an "optional" starter relay to solve this problem. You can go to any auto parts
store and get a starter relay instead of getting the Yanmar version (its hard to find, anyway. the part number isn't in their part book).
Hook the start wire from the start switch to the pull down terminal on the relay. Connect the other pull down terminal to ground. Connect one of the switched terminals to the battery
by building a cable that connects the main battery cable at the starter to the relay. Connect the other switched terminal to the starter solenoid, and you're done.