I recently purchased a 1985 303 with the 2GM Yanmar engine. I am having some difficulty getting the engine to start. It does start, but only after several attempts. I've read the manual and see where with the 1GM you are suppose to pre-warm up the engine first, but I can find no instructions on pre-warming this model and my throttle does not have the warm-up knob. I have the "B_Type" control panel. The manual does not identify what the toggle switch labeled # 8 is for, and I am wondering if this has to do with the pre-warming. Any thoughts would be appreciated.
The switch you are referring to should be the "lamp test" switch. It should be a momentary style that will illuminate your warning lights to make sure the bulbs are working. The factory Yanmar manual is less than helpful for a lot of things. Seloc makes a pretty nice Yanmar manual, and I'm sure there are others out there.
My 2GM20F starts within a second or 2 if the temp is above 60°AND there is no air in the fuel lines. Much below 60°, and it can take a few seconds. If you have a small air leak, it can take quite a while or will never start.
I would recommend getting a good service manual for your engine, and going through the troubleshooting process. Many starting problems are simple fuel delivery issues that may be remedied by bleeding air from the lines, replacing a fuel filter, tightening connections, or diagnosing a weak or malfunctioning mechanical fuel lift pump. The copper washers in the fuel delivery system are a common source of minor air leaks.
Good luck!