Prop help

[STRATOS BASSN]

I would like some help.
I have a 1997 Stratos 201 pro elite. 20'2 ". Dual console.
I recently removed a 1989 Evinrude Xp 200. It was running a 24 pitch 4 blade prop. I was getting 65.2 on GPS with it.
I now have a 1995 Mariner EFI 200 on it. I started out with a 4 blade Trophy 23 pitch. And I was turning 5600 RPM's and running top speed of 56.7.
Today, I swapped the prop to another 4 blade 25 pitch, and I was still turning 5600, and picked up to 58.4.
My question is, or maybe just looking for opinions,
I'm trying to figure out why it's considerably slower.
Should I swap to a 3 blade, or go on up in pitch?
Please give me your opinions.
Thanks.

 

[alldodge]

I'm not an outboard expert but the 89 Rude was 2-stroke and if the 95 Mariner is 4-stroke its all about HP to weight ratio. As an example, a 2007 Seadoo 4-stroke with 155 hp motor goes no faster then a 2001 Seadoo 2-stroke with 130 hp motor. The 4-stroke motor weights more then the 2 stroke.

Also be aware that Boat US has several write-ups about boats sinking during a heavy rain because, the boat was not design to have a motor that heavy on it when built.

 

[steelespike]

Why did you change the motor?
Have you tried raising or lowering the motor?
Don't assume because it is a fresh application that it was done right.
If it is a EFI you should be able to trouble shoot the setup.
You might want to start with the compression on each motor.

 

[STRATOS BASSN]

Thanks for the responses. Both motors are 2 strokes.
I changed the motor because I was having idling issues with the rude. And I just like mercury better.
The compression is 105 to 110 on all six.
I have not raised the motor yet. I have the cavitation plate about 3 inches above the bottom of the boat.
However, now that you mention it, the rude would blow out coming out of the hole. The Mariner doesnt.
So maybe it is a height issue.

 

[alldodge]

Three inches above the bottom is a bit much if not using some kind of extension box. If the new motor does not have the same shaft length as the old, then there is your problem