2GM Yanmar tops out at 2400 RPM

D

Dubo

.
Oct 26, 2010
86
Hunter 340 Deltaville Va
The last few times I have taken my Hunter out this year I noticed when I max out the throttle the tach reads 2400. I shifted to neutral and repeated the acceleration and the RPMs went beyond 3000. My first thought was the fuel cable slipped but if it did I should get close to the same reading on the tach. The fuel filters are changed yearly so I know they are not clogged. Is this a
sign of a tranny problem or perhaps a pump? Is there another test I can do to narrow this down?
2400 is my motoring speed by chance. Should I just live with it and accept it as part of owning a boat or is there something more destructive in the works? :what:
TIA,
Dubo
 
Dave602

Dave602

.
Jan 22, 2008
320
Hunter 29.5 Gloucester, VA
Could be one of several things. Crusty prop, dirty bottom or your mixing elbow could be clogging. Ive had those symptoms with all of those
 
Roland5048

Roland5048

.
May 12, 2004
1,505
Hunter Cherubini 30 New Port Richey
I have to agree with Dave. Also, what does the exhaust look like when you max out the RPMs? White, blue, black? Don't learn to live with it for the sake of your engine and your pocketbook. Find out what's going on.
 
Alan Gomes

Alan Gomes

.
Nov 22, 2011
1,259
Ericson 26-2 San Pedro, CA
Additionally, you should pick up an inexpensive optical tach from a place like Harbor Freight. The Yanmar tachs are notoriously inaccurate. This is not to discount any of the advice above, by the way. But it would be good regardless to know what the true rpm is and it unlikely that you are getting that from your tach.
 
Warren Milberg

Warren Milberg

.
Dec 1, 1999
2,391
Hunter 28.5 Chesapeake Bay
My bet is on a clogged ,or clogging, mixing elbow. When was the last time you changed it?
 
D

Dubo

.
Oct 26, 2010
86
Hunter 340 Deltaville Va
I haven't replaced the elbow but have removed it for cleaning when I replaced the exhaust tube last year. Seemed to to be fairly clear. The exhaust is typically grayish-white when it is noticeable. No real smoke trail.

If the prop is fouled, wouldn't the RPMs still be about the same, just less speed?
 
Roland5048

Roland5048

.
May 12, 2004
1,505
Hunter Cherubini 30 New Port Richey
Dubo said:
If the prop is fouled, wouldn't the RPMs still be about the same, just less speed?
Click to expand
No! Your RPMs will be lower. The engine is working harder and can't get to full rated RPM. This, usually, results in black exhaust smoke from unburned diesel. Take things one at a time. Check your running gear, first, them get back and post your findings.
 
Ken13559

Ken13559

.
Oct 29, 2005
2,363
Hunter Marine 326 303 Singapore
When you cleaned the mixing elbow, did you notice how large or small the exhaust passage hole is? It may look clean but could be constricting.
 
dziedzicmj

dziedzicmj

.
Aug 13, 2012
533
Catalina 270 Ottawa
have you considered that you might be over-propped? i.e. your prop is too big or has too much pitch.
mdz
 
D

Dubo

.
Oct 26, 2010
86
Hunter 340 Deltaville Va
I thought I'd update this thread for other's benefit. Dave was right with the crusty prop suggestion. The prop wasn't overloaded with barnacles but enough to effect the water flow. I scrapped the prop and took her out and was able to exceed 3000 RPM's in gear. I wouldn't have thought the RPMs would drop but it did. Lesson learned; speed and engine RPM are reduced with a dirty prop.
This was an easy fix and didn't drain the bank.
Thanks!
 
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Ken Cross

Ken Cross

.
Oct 24, 2010
2,405
Hunter 30 Everett, WA
I had a simular problem. The exhaust I removed and ran water through and it didn't appear to have a problem, but when I separated the exhaust parts it was pretty obvious. a 1/4 inch or less passage for exhaust severely limits engine performance.
I'll attach a pic. Please take note. The coupler between parts is a combination of left and right hand threads (like a turnbuckle.)
That's why the old one is broken.
Ken
 

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