Transmission slipping or something else?

[Sandy Jean]

I have a Yanmar 4JH2-TE Engine and a Kanzaki KM4A Transmission. In neutral I can rev the engine to high RPM's when I put it into gear and throttle forward it barely goes up to 600 RPM's. I have to go into neutral and then forward several times and then when it grabs it goes...fast! This is an intermittent problem. Anyone have any ideas what the problem could be?

[lamadriver]

Does it go into reverse? if so do you get full rpm in rev?


fwd clutch plate comes to mind, though it could be as simple as a shim.

[Sandy Jean]

Yes it goes into reverse but when the symptoms are present, it reacts the same in reverse as in forward...no or little RPM's while in gear yet full run up of RPM's while in neutral.

[a64pilot]

I have to think something is wrong not with the transmission but with the lever, no matter what happens to the transmission the engine ought to get fuel, now if its getting fuel but the transmission is holding it back, then the engine ought to sound labored and be blowing black smoke, is it?

[TheOffice]

shift it at the engine. Many of the Kanzaki trannys have a lever with a round hole on a round shaft. Over time they loosen. Check the fluid too. When was it last changed?

[Sandy Jean]

Originally Posted by TheOffice

shift it at the engine. Many of the Kanzaki trannys have a lever with a round hole on a round shaft. Over time they loosen. Check the fluid too. When was it last changed?

Fluid(oil) new last oil change. Will try shifting at engine when back on board. Thank you

[lamadriver]

That was my next suggestion was goign to be disconnect the cables and shift at the engine.


LD

[Cadence]

If I understand you? It sounds like the engine is loading down not a tranny problem. Fuel starvation would be my first thought.

[rogern]

Single lever control? Shifters can wear out, mine did (Yanmar 4JH-2TE w/ KBW20 transmission). Different symptoms, but +1 on operating both transmission and throttle at the engine.

[topmast]

Assume you have a two lever.. Can you inspect the internals at the bridge? Maybe a clip is loose and cable interferes with throttle. Or cable actually bends (just before breaking) between clip on and lever arm. Isolating at the engine and trannie and manual run will eliminate deep mechanical problems maybe.

[JimsCAL]

A slipping transmission clutch would be high revs but low propeller RPM. I'm in the camp that's suggesting the shift lever mechanism is the problem. Since it seems to "fix" itself after shifting a few times, it doesn't sound like fuel starvation.

[bongo]

I would agree with others to try shifting and throttle at the engine. As JimsCal said above, slipping would cause high revs. So, it is NOT slipping most of the time, it is grabbing.

But, if it is not a linkage adjustment:
I just recently had a similar problem on our boat, and it turned out to be prop fowling, (turns out there has been a lot of that this year in Puget Sound). I could not get higher RPM, she would barely move, could not maneuver, engine blew black smoke. Diver scraped blades, (it had been out of the water only 8 months prior), and VOILA!

[peedee]

It could be an intermittent fuel supply. My son had this problem, usually when putting engine into reverse to come alongside berth! Eventually found to be caused by broken springs in the fuel pump.

[Sandy Jean]

Thanks for all the suggestions. Finally tracked down the problem and it was the boost compensator in the governor. Not all 4JH2-TE engines have them so it was a mystery to a lot of people. It needed a slight adjustment and all is well.