All or nothing?!?

I can't help but notice the odd throttle response on the rig I just bought. Takes off good, nice top end, but in between something weird happens. As I ride along barely on plane at 20 mph, I push the throttle ever-so-slightly to go just a little faster. The engine begins to sound much louder, roaring instead of purring. It seems like the speed and RPM increases a lot all at once as the speed quickly gets up to 30. If you try to back it off just a little, the engine slows down and runs quiet again and speed drops back to 20. It seems really touchy in that mid-range zone. Is this just because it's spinning such a steep prop? (28" chopper) It annoys me a little. my friends are scared I'm going to kill them doing 70+, so we like to cruise around the lake between 25 and 30 before I drop their wussy asses off and go open it up! Is this normal for a stock 200 XRi EFI? -Chad

[daytona]

Hi Pyro That sounds to me like an artifact of the cleaver prop coming on plane with a high propshaft height. A chopper will help but when a boat is first rolling onto plane and you try to hold it just beyond, ventelation will happen. Lowering prop height will fix it but without a hydraulic jack plate to raise it back up, it will kill top end. I know you probably know all this but i had fun! rick

[jimmyb]

most merc 2.5L motors have weird resonance sound at around 3000 rpm. I am pretty sure it has to do with the intake/exhaust pulses...

also, what daytona said could be the case as well...

dont you hate that "barely on-plane" cruising?

I'm talking about running with the plate all the way down, motor trimmed in. It DOES ventilate, and throw a big foamer right after it comes on plane, but only for a second, then it bites OK. Like jimmy said, it's like a loud "resonance" accompanied by some acceleration with the RPM increase. If I try to back off just A LITTLE, it sounds like the motor has quit, as the rpm drops and the loud resonance goes away. The boat slows down to 20 mph, the merc purrs like a kitty. It's running a 28" chopper, not a cleaver. I have a hydraulic plate, I leave it all the way down, unless I'm doing some speed runs. Does anybody else have trouble maintaining a crusing speed between 20 and 30 while running a speedy prop? -Chad

Hey, by the way, since I changed the tach's setting to "4", it looks like it IS right at 3000 rpm that it starts to get loud. Another reason why I think the old tach setting (3) was wrong. -Chad >==FFWD===>