1GM10 sluggish under load

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J

Jon Zaimes

Recently the Yanmar 1GM10 in our '80 Hunter 27 has been sluggish under load. In neutral it easily reaches the top RPM (3600) with plenty to spare. But in forward at full throttle it tops out at about 2800 RPM. Oddly, in reverse it will reach full RPMs without any problem. Exhaust appears to be spewing some black stuff into the water when under full load. Engine starts OK and runs OK. Have just checked the air filter and changed the fuel filter. Also have just brushed the hull so it is reasonably clean (at least as far down as the brush reaches). She seems to be moving along fine under sail. Ideas? Jon Zaimes "Airwaves" sailing out of Cambridge, MD.
 
B

Brian

Black smoke

I had the same problem on my Legend 35. I put the mask on and found the prop was loaded with barnacles. I scraped them off and had no more problems....
 
T

Tim Schaaf

Overload

It could also be overloaded with auxiliary equipment.....a big alternator would be a suspect. It does better in reverse because the prop is less efficient and because it probably has a different reduction ratio.The prop probably spins a bit slower in reverse, so there is less load. Check the manual for this.
 
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Tony

Sluggish

Jon, Had the same problem on my hunter 27. Turned out to be the transmission was slipping. I also think it was ok in reverse. Tony
 
H

Howard

Check the prop

I had the same problem on my 78 H-27. Black sooty smoke , loss of power in forward ect. Check that the prop is turning freely when the engine is not running. If it turns smooth and easily try cleaning the barnicles (sp) of the prop with a 2" flexible putty knife. A snorkel and a mask helps. Put a length of string through the handle of the knife and around your wrist. WEAR FABRIC WORK GLOVES. If the shaft dosen't spin easily when the engine is off check the engine alignment. If you hit something with you prop or picked up a line in the prop you might have bent the strut or shaft. This can also cause overloading. I once bent my strut and was able to straighten it with a big monkey wrench. If you do this be aware the strut can snap, but it works 75% of the time. Another possibility is the cutlass bearing is shot and has jammed. For the above items you will probably have to pull the boat out of the water. Let us know how you make out. Howard
 
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