Q on Johnny Motor

[quackaddict1]

Hey guys, a bit of an odd thing happened to me the other day while out fishing, not a huge deal but for all I know the start of something. So I have been doing some testing on motor height and props as of late, and I thought I had everything dialed in (motor 1995 28SPL) with the boat running 22ish MPH at 5600rpm (fishing load, two guys). Since I had plenty of bite, I moved the motor up 1/2 inch on my jack plate. With that, I got 5700rpm and close to 23mph @ WOT. The motor ran like that for almost the whole trip across the lake we were fishing last (slight chop, about a mile run). When we rounded the last corner and got into calm water, the RPM's from the motor (no movement of the shift/throttle) began to dip, the motor then lost RPM's until it got to 5300rpm. I thought the lack of chop might of created the loss of RPM, but when we ran back all I could get out of the motor was 5300RPM, and the conditions on the lake still consisted of light chop. The motor idled fine, and I check the butterfly today to verify that it was opening all the way.

Any thoughts on why the motor just up and lost RPM's? Load was exactly the same, we had a slight (less than 10mph) headwind on the way back, but no matter how I adjusted load we couldn't get it back to 5700. Maybe I am making something of nothing, but I finally got the dang thing running good, don't wanna mess up a good thing