1981 Hunter 33, Yanmar 2GM. can't make RPM's over 1800????

A

azambella

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Sep 27, 2008
155
Hunter 33 salem
1981 Hunter 33, Yanmar 2GM. can't make RPM's over 1800???? Black smoke too.

Always been this way. Clean bottom & gear. Motor makes 3600 RPM out of gear.
The obvious thought____Oversize propeller one way or another diameter or pitch or both...

I have made many Inquiries on-line, with propeller people, Hunter and hunter dealers and I have yet to get the same answer twice about what propeller should be on this boat.

Is there anyone with a (Cherubini) Hunter 33 and the Yanmar 2GM combination that can actually get anywhere close to the 3600 RPM in gear? If so, what propeller do you have?

FYI...
I prefer a fixed prop.
 
B

Benny17441

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May 24, 2004
7,179
CC 30 South Florida
Make sure your propeller is not bent or otherwise fouled. Make sure the shaft is turning freely. Has the transmission been replaced? With a reduction of 2.6:1 for the standard 2GM tranny a prop size of 2 blades 16X9 should be a good a good base size to start with. Define what type and the size of your current prop for comparison.
 
Last edited:
kloudie1

kloudie1

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Nov 6, 2006
10,107
Hunter 34 Mandeville Louisiana
Ya need to get the gearbox ratio.. should be on a plate on the side of the gearbox. Should be a KM-2A box but could have any one of three ratios.. Some 33's came with a 2QM 20
 
Franklin

Franklin

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Jul 20, 2005
2,422
Whitby 55 Kemah, Tx
I had a problem with my Yanmar not being able to get over 1800 rpms. It was either the pump or the injectors. Sent both off to get rebuilt/cleaned and all is good after that. I am assuming the filter is good.

To determine if this is your issue it is very easy: you should be able to reach 1800 rpms about half throttle while in gear (out of gear is worthless test). If you do but the more throttle you give and no increase in rpms, then this is your problem. If you engine does a gradual increase all the way to full throttle then it is the prop.

Don't rely on the smoke to tell you. Diesel engines can build up soot easily if not used properly (wrong size prop being one reason -- running at idle to charge the batteries a lot is another reason) and it's the soot that makes it black.
 
A

azambella

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Sep 27, 2008
155
Hunter 33 salem
Thanks

We have the 2.6:1 reduction. A 16" propeller will physically not fit.
The Boat definitely has the 2GM motor.

All the research I have been able to do tells me the original was 14 x 12 2 blades. I don't know what's on there now
I will have to wait till I can unwrap and have a look. 3 big mouse ears though for sure.
I will also look into the fuel supply test.

Thanks again

Z
 
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