Hi Kevin, In addition to making sure the transmission is fully engaged (We had that issue too, for me, it was solved with a simple cable adjustment), it sounds like you should jump in the water and take a good look at your prop. What you need to do is grab the blades and wiggle them against the folding axis. So, not following the folding movement, the other axis -> back and forth. If the tip moves more than 1/8 - 1/4 inch the hub and blades need a rebuild.
The Martecs only go so long before needing a rebuild which consists of reaming the pivot axis hole and installing a larger diameter pivot shaft. It sounds like a big deal but it's not: Last time I had it done Martec did it for $80.00 plus shipping. The 3GM30F (I have one on my boat) is a small displacement engine (950 CC) and by diesel standards: A High revver. It needs to cruise between 2800 and 3000 rpm and should run about 3400 rpm flat out. If it's in good shape and it can't achieve that something is amiss: Too much pitch on the prop / dirty and draggy bottom / combination of both. When I had my prop redone Martec sold me higher pitch blades saying it would "Run better" It didn't. All I got was cavitation and vibrations. Going back to the original blades solved the issue. Yes, the blades with more pitch were pitted (Obvious sign of cavitation), they looked like they were infested with little crustaceans that don't exist in a lake. When Yanmar says you should run the engine at those RPM they are not kidding. Prior owners of my boat ran it at low rpm too often and turned the engine into a "Hard Starter" (What the local mechanics called it) as not enough load and RPM caused excessive carbon deposits / fouled the injectors / messed-up the whole thing. it was literally a 5-10 minutes battle to get the engine running on the first start of the weekend every time we used the boat when we first got it. I "fixed" the issue by running it at prescribed RPM / running it wide open for at least 10-15 mins every weekend / using Diesel Kleen Power service injector cleaner. It took over 20 gallons to really make a difference but now the engine starts within a few seconds every time when cold and immediately fires-up for the rest of the weekend. Good Luck, -Francois Rivard 1990 34+ "Take Five" Lake Lanier, GA
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