Porpoising on mx14 /cobra with 115 merc and lift plate

[gtrumpet]

I have a problem with porpoising after planing out, the boat then smooths out at high speeds. I'm running a 115merc inline with 19p prop, ive only opened it 2/3s of the way, so i don't blow the motor with that low pitch prop The merc is mounted on a lift plate with 8" setback and 3-4 inches of lift. Would removing the plate eliminate the porpoising, im thinking the plate move the center of balance to far aft. As far as the plate making the boat stable at high speed, it accoplishes its goal wonderfully.

any advice would be appreciated.

thanks,

Will

[Blizz]

That's alot of setback for that little boat. Lots of the smaller boats like very little or no setback at all. Play with your trim abit while at slower speeds you might be able to find a sweet spot for it but i think you need to bring the motor closer to the boat.

[BullittBen]

The 19p prop is not necessarily too small. Don't go by the original specs for that inline. Turn your max timing down to 21* (no more than that) and make sure that your rpms are at least 5500 at WOT. My 115 inline only turns around 5100 WOT with a 19p on a 17' boat and that is way too low rpm. I'm still working on the rest of my setup, so I don't know what prop will end up being ideal.

Watch your water pressure with that jackplate also. An old inline has very low pressure anyway, and you may starve it at high speed if you're not careful.

Does your inline have power trim? Mine does not, but I am in the process of rebuilding a later model mid to get it. The problem I have with a jackplate and no power trim is holeshot. It's hard to get going if the jackplate is up and you can't dig in the trim. That's why I say I'm still working on setup.