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Re: Full throttle needed to start Yanmar 2GM20F
I have the same motor as the OP. I always do a cold start at 3/4 throttle, throttling back to idle immediately after start, as directed in the manual. It's over 20 years old, does not have glow plugs, and has never had a starting problem (in the moderate SF Bay Area climate). Kicks on the first crank every time! Once warm, it starts immediately from idle position.
Sounds like a good Yanmar mechanic is in order for the OP. If he is in the Bay Area, List Marine will sort it out in short order. I'll bet they will also tell him to cruise at 3000 RPM when it is running properly. Makes for a happy 2GM20!
Opposite end of the country. I am in NY Long Island Peconic Bays area, pretty much the same climate. My engine at this point stalls after start if I pill back to idle immediately, I have to keep it in the 2000 to 2500 revs until it smoothes out. And, when warm when its running it sounds like there is a man with a hammer in the engine (mechanics called this fuel knock).