Vz225tlrd vmax 225 hpdi loss of 200 rpm's

[mparsley]

Have checked compression, replaced plugs, changed filters, serviced injectors by Brucato. All cylinders are within 1 lb of one another.

Still have lost 200 rpm's on top end. I am at a loss and have no clue what this could be. Could this be electrical. #1 plug is blacker than all other plugs like it is running rich but it shouldn't be as injectors and filters have been serviced. Could it be a coil or plug wire or something else electrical.

This motor runs great. I am just missing the 200 rpm's I used to see at top end. I was getting 5900 and now get 5700. I even raised the jackplate to see if it could turn more rpm's but it just won't. It just stops at 5700.

[Rich Z]

Wot speed drop off also?

[mparsley]

Yep from 68.6 to 66.4 gps.

[GM250]

how many hours on that prop also is humidity hight?

[mparsley]

Humidity is not high. We actually have had nice weather this week. Prop has unknown hours bought it second hand about 4 years ago. It is a 25t-1. But I tried to rule that out by raising the plate to gain more rpm's even if that were the problem but no luck. It is like it hits an imaginary wall at 5725 rpm's on digital gauge.

[BigJfrank]

I've had the same problem. Hot weather. Water is still very warm even though we're running 10-12 degrees cooler than we were 4 weeks ago. Once the water cools, I bet you get it back.

[mparsley]

Water here is 76 degrees air temp. is 90 with low humidity. This has never been a problem even in 95 degree weather and 85 degree water. I hope you are right though.

Any other ideas as this engine was set up in the heat of summer and has always got 5900 rpm's, as required, even during the hottest part of summer with high humidity.