Loss of power in forward.

[1mcarlson]

Last night I was motoring back to marina in 2 to 3 foot swells and no wind on Lake Michigan. After about an hour and half rpm dropped from 3300 to 2000 rpm and wouldn't climb back up. No smoke, motor sounded normal. Put in nuetral and reved up to 3300 rpm then back forward, same problem wouldn't climb above 2000 rpm.
Made it back and next morning changed hp fuel filter on 2GMF yanmar. With boat tied off in nuetral 3300 rpm, in forward 2200 rpm, in reverse 3200 rpm. Checked prop underwater, spins easy.
Any ideas?

 

[Pat]

It sounds like my Volvo which has a light that read's "reduced engine performance" just as it is loosing power as you 'try' to
get on the freeway.....pat.

 

[Sailgunner]

ck fuel filters

 

[Benny17441]

The engine reacts only to loads, it does not care whether it is going forwards or backwards so there is a difference in the loads between the two modes. With the transmission in neutral check and see if the shaft spins freely in both directions. You do have a fixed prop, correct? Check for play in the shaft and also check for any noises coming out the transmission or packing gland in both forward and reverse. How about boat speed, was the reduction in RPM accompanied by a loss of speed? Is the prop fouled in any way? Could it have struck something while underway? Does it smoke at Wide Open Throttle under load? Any noticeable changes in vibration? If everything checks out then attack the loss of RPM as you normally would. Replace fuel filters and make sure that the screen in the pick up tube is unobstructed. Sustained 2 to 3 foot swells can be enough to dislodge sediments inside the tank that might restrict fuel flow. I have to honestly say that I seldom race the engine in reverse and when I have I have not checked RPM to be able to tell what difference between forward and reverse would be considered normal. Because of the governor action checking RPM in neutral seldom reveals anything. Hope some of this helps.

 

[uncledom]

Only two thoughts, fuel flow or throttle lever problem. Good luck.

 

[1mcarlson]

Ok, changed high pressure fuel filter and cleaned out separator bowl. Added fuel injector cleaner (diesel) but still have to check pick up screen in tank. Dove down shaft spins freely both directions. Put it in forward and spins easy in one direction and did same for reverse. Took it out yesterday motor only out of marina and ran in both forward in reverse and problem seemed to disappear. Hopefully this weekend try doing a long motor cruise and see if problem returns.