1GM10 not happy

[CarolinaCalm]

1gm10
We have a new to us (Fall 2015) 83 Pacific Seacraft Flicka with a repowered 1GM10 in 1999. After purchase we have replaced the complete cylinder head assembly (significant head corrosion and exhaust port blockage), impeller, engine anode, fuel lines, oil and fuel filters. Engine starts reliably but will only get to 2500 rpm in forward gear with full throttle. The engine does not smoke or exhibit any other problems but SOG is slow (I know it's not a speed boat) and way less than hull speed all the time (max 4 knots if lucky). Temps on the shaft/transmission are cool to the touch so we don't think there is a drive train problem.... engine is responsive to throttle and in neutral easily goes to 3600-3800 rpms so we think the tachometer is OK/fuel supply is OK. At this point trying to figure out what to do next.
Based on this site I have ruled out the hull (clean and repainted and launched in May 2016), the propeller is a two blade prop that appears original so it is not clear that it is over propped. So at this point I have two questions:
1) what additional things could explain this?
2) what are the effects to run the 1GM10 under the target RPMs of 2900-3000 while using full throttle?
Loving the Flicka in NC

[meridian28]

I take it this was purchased without a survey. I would go with an over prop issue.

[CarolinaCalm]

It was surveyed but I was not able to attend. Survey stated that engine started, idled , and powered the vessel with no noted issues. Pretty weak. Later when we disassembled we found significant corrosion issues so the survey was useless to me wrt the engine but was thorough in all other respects.
I recieved one reply from a different site suspecting the throttle linkage with the thought that if the engine is not smoking then the linkage could be limiting fuel. I will chase that thought and the next will be the prop. Thanks for reply

[GordMay]

Greetings and welcome aboard the CF, CarolinaCalm.

[sony2000]

Check out the props on other Flickas, on the hard. What is their pitch?
Are they 7",8", or 9"? What is yours? If you lowered your pitch an inch, you may end up with 2800-2900rpm. I'm tending to think your rebuild was good.

[roverhi]

If the engine runs to 3600 rpm easily, it could be too small a diameter and/or pitch prop. Sounds like the engine is working fine. Unless the transmission is slipping, the only other thing is the prop. A Prop shop should be able to increase the pitch of the prop by an inch or more which shouldn't affect performance all that much if it is in fact currently the right pitch.

[sony2000]

Originally Posted by roverhi

If the engine runs to 3600 rpm easily, it could be too small a diameter and/or pitch prop. Sounds like the engine is working fine. Unless the transmission is slipping, the only other thing is the prop. A Prop shop should be able to increase the pitch of the prop by an inch or more which shouldn't affect performance all that much if it is in fact currently the right pitch.

[CarolinaCalm]

Thanks to all that replied. Turns out it was a throttle linkage problem. Engine now is able to cruise along at 2900-3000rpm per Yanmar operating guidelines for continuous rating and also can hit the max rpm of 3400 for short periods.