1991 Mercury XR4 low rpms at WOT

[Gray2.4]

Hey all, I have a 1991 Mercury XR4 on a 18 ft bass boat that will only run 5000 rpm at WOT. Boat weighs 1200 lbs dry, I calculated total weight to be somewhere around 2200 lbs. I had a 26 tempest before and quickly realized it’s way too much prop, was only getting 4500 wot. Now I dropped 4 pitches expecting to gain 800+ rpm, instead I barely got 500. Checked spark plugs on all, compression is 130-140 on every cylinder, has the 1.87 lower. I’m just lost cause it should be turning it better than it is, any thoughts? Thanks all

 

[Faztbullet]

Picture of boat and engine set up on transom

 

[Dukedog]

1.87 gear? has it been changed?

 

[Gray2.4]

Yes, 1.78 lower locked up this spring, think it may be a bearing but decided to get a 1.87 SEI lower for now, might repair it later. attached pictures of boat and motor mounts. Can’t trim motor down all the way while it’s on trailer, will lower the trailer all the way down when I get back to see if I can get the motor down more.

 

[Faztbullet]

Whats the ptch on that Temptest?

 

[Gray2.4]

22 Tempest with flo torq hub kit

 

[Gray2.4]

AV plate is just about 1.5 inches above pad of hull. Might be able to go up one hole to get 2.25 above pad. How many rpm would one hole increase?

 

[Dukedog]

start point.. boat level, motor level... center of prop shaft 3 1/2 inches below pad....