Help! Repower to merc 150 4 stroke lost 5 MPH

[Gsmith223]

I have a 2007 war eagle 962 tomahawk with 6 inch bobs jackplate that I recently repowered from an 1994 XR6 150 to a new 2018 merc 4s 150. This is the older style war eagle with the padded hull.
I am running the same prop its a 21 Yamaha M1 series but it fairly rough shape, and I have lost about 4-5 MPH. Is the 4 stroke not as strong as the old XR6? I am only running 48 MPH at 5500 RPM now and the hole shot sucks, where I was running 52 MPH at 5600 RPM previous to the repower.

When I first got the boat it had a 1998 Merc 150 XRI and a worked tempest plus 23 pitch and the boat would hit 60. I ended up blowing that motor and replaced it with the 1994 XR6 but it wouldnt turn the tempest prop but 5200 RPM, so I put on the M21 Yamaha and it brought it up to 52 mph at 5600 RPM. I wanted a new motor so I repowered to the 4 stroke and instantly lost another 4 MPH. I realize that another prop is in order but I am at loss for why I lost so much speed. Can someone educate me a little bit? I am thinking that I need to go to back to the 23 pitch tempest but if the XR6 wouldnt turn it I am worried the 4 stroke wont either. I do feel like the boat isnt getting all the way up on pad though. I cant trim it as high now as before.

Also I have the chance to get a croxton Razor 22p but I am not sure how it will compare to the m1 or the tempest.

Thanks in advance for any help.

[mdtritn21]

For starters you changed lower unit gear ratio from a 1.87 to a 1.92 on the four stroke and that cost you 1-2 mph. It might turn the 23" but probably not to 5800 rpms like you need. That 21 m is trashed right now so a repair should help bring your rpm's and speed back up.

[Gsmith223]

For starters you changed lower unit gear ratio from a 1.87 to a 1.92 on the four stroke and that cost you 1-2 mph. It might turn the 23" but probably not to 5800 rpms like you need. That 21 m is trashed right now so a repair should help bring your rpm's and speed back up.

Thanks for that info, I also checked and it appears the motor weighs about 50lb more as well.

Would it be better to get the 21 m worked or just switch to a merc prop? I noticed the venting is a little different on the Yamaha prop and I wondered if that could be an issue on the 4 stroke vs the 2 stroke.

[mdtritn21]

I'd get the M worked you can always sell it. Venting only matters on take off.

[texasbass1]

Try a Tempest 21 if you can find one. Works great on my 150, I plugged the vent hole. Don't need them with the 4S according to Merc and I have a great hole shot. I tried a 23 Tempest on mine but it was a dog out of the hole. Speed was the same as the 21 with lower RPM's. The 21 is the ticket for me

[Gsmith223]

Talk to mark he recommended working the 21m. In the mean time I was able to adjust my hotfoot stop screw to give me more throttle and now I am just barely touching the rev limiter.