2006 21 i-class / 300 hpdi setup

[21i]

I have a 2006 21 I-class with manual jack-plate, 2006 300 hpdi and 27p T1 prop. I can't seem to get the engine rpm above 5,600. I've adjusted engine height in 1/4" increments from propshaft at 3.5" below pad to 2 1/4" below pad with no change in rpm or water pressure. I start losing speed at around 2 3/4" below pad with the sweet spot seeming to be at 3" to 3 1/4" below pad. I top out at 75 mph at 5,600 rpm at this setting with just myself and full fuel tanks and 80 degree air temp.

I've had the prop worked twice to try to spin to 6,000 rpm but neither time has made any difference. Do I need to try a different prop or could there be a throttle positioning sensor problem that isn't allowing the motor to spin any higher than 5,600? Any other suggestions?

[silververt]

I've got the same rig as your's except mine's a 07. Not sure of the actual motor height, but looking at the jackplate "split", there are 12 notches showing. Have no problem spinning the motor to 6000 rpm's

[LuckyMesscun]

Still tinkering with my setup a little also. Mines not an I Class but same powerplant. 6,000RPM's no problem. So far runs like a champ. (knock on wood)

[21i]

Changed plugs yesterday, and had dealer check hotfoot and throttle cable at the motor. Everything was adjusted properly for wide open throttle. Tried a stock 27 T1 and had my worked T1 measured out by the prop shop here and its all supposed to be good, with a little less cup than the stock T1. Managed to get the jackplate up to 2 5/8" propshaft below pad resulting in a best of 5,600 - 5,700 rpm (briefly) at 75-76 last night with air temps in the 60's and slight ripple on the water.

Maybe this is just the best my motor/rig will do, although there are supposedly plenty of people turning stock T1's at 6,000 under similar conditions.

[silververt]

My motor would turn the stock 27T1 over 6000 rpm, had to have it worked to bring rpm's down? Something isn't right, you should be easily able to 6000 rpm.

[21i]

I wish I knew what the deal was. Dealer says motor is performing as it should be. Prop guy says motor should spin this worked T1 to 6,000 easily. Buddies say quit worrying about 300 measly rpm. I say the motor is rated for 6,000 rpm max and I'd like to run it at it's max potential. I just don't want to reduce pitch to get there. Looks like I've hit the wall with what I have unless we can caress the prop a bit more. Maybe I've just got a weak 300???