Bizarre Engine behavior

[Dan K]

During recent spring maintainance, I noticed that one of the cylinders of my 25XP was running at 130 degrees whereas the other two were at the expected 160.  As a result, I replaced all of the injectors and the engine runs like a top and revs to 3200 rpm.  On our first cruise of the season, we noticed that the engine tops out at 2200 rpm but pushes the boat along at 6.5 knots.  I've checked the numbers on the new injectors and they are identical to the old ones.  Any suggestions on this problem would be apprecited.

[Jim Price]

Dan, I am not the expert as you will find out from others, but the fact the engine is running up to 3200 rpm, I assume out of gear, is normal.  You pretty much cannot over rev the engine as the design will self limit.  Your RPM of 2200 at 6.5 knots has to do with your prop pitch.  I definitely am out of my league here but prop pitch effects the maximum RPM the engine will achieve and of course determines either the "low end power" or "top end speed" of the boat.

Others can give you more intelligent answers but pushing along at 2200 and getting 6.5 sound nice to me.  I have to turn 3000 on flat water to achieve the same but the boat has great low speed torque in tight places.  Not sure of my prop pitch - maybe some day if we ever get enough water in the lake to haul again I will find out.   

[Craig Illman]

Dan - I expect you're overpitched on your prop. I'm a bit overpitched too, I get 6.7 kts at 2700 rpm, 6.2 kts at 2100. Getting any smoke at max rpm? I have a 3-blade 15x10.5 & my compression is on the low end of tolerances, about 370psi.

Craig

[Jon Schneider]

Dan, what was the max RPM (or the RPM that got you to 6.5 kts before the new injectors?  I'm assuming you're noticing a significant difference before and after the injector replacement.  BTW, I'm curious... how did you actually measure the operating temp on a cylinder by cylinder basis?

[Ron Hill]

Dan : The first thing that I'd suggest is that you contact Hank and borrow the Fleet 12 laser tack.  That way you can check your instrument rpm against what the engine is actually turning. 
Anytime you talk speed I assume that you are talking about knot meter speed (thru the water) and not GPS speed (over the bottom).
From you hull # I'll guess that you have an M25(21hp), unless a PO changed to an M25XP(23hp).
From you post are you saying that you have lost 1000 rpm? Was the earlier 3200rpm in gear, like the 2200 rpm and everything else remained the same?