Mercury 150 4 stroke. Not Pro Xs model

[BJ Hicks]

Z518 with the non Pro Xs 4 stroke 150. Top speed used to be 55-56 now struggles to get to 50-51. I am looking for any ideas or help that I can get on this it would be greatly appreciated. I had to have lower unit replaced and some engine work done a few months ago. Afterwards could only run 46-49mph and would drop a couple hundred rpm’s. Took to shop and everything checked out ok and they changed fuel filter which seemed to fix the rpm’s issue and it stays at 5800 at WOT now. They lake tested and hit 55mph no problem. I picked up boat and could only hit 50-51. Finally after couple days of running it, while going down lake RPM’s 5800 it picked up and shot to 55.6 in and instant like you shifted to another gear. Rpm’s still stayed at 5800. Had to throttle down and could never get it to do it again. Back to 50-51 tops. Shop is a good shop so please no dogging them I know this is intermittent problem and going to be hard to find, I am just hoping somebody has had same issue and could steer me in right direction. Thanks.

[EuropeanAM]

Please take a moment to review the Announcements at the top of the Forum, and be sure to provide the Required Info (serial number) when posting. Thanks!

Did the gearcase FAIL, or was it replaced due to damage/collision? Prop changed, worked, or damaged?

What prop are you running?

Trolling motor or battery changes in boat?

Part number of gearcase installed?

[BJ Hicks]

Serial number 2B365563. Just like the boat is setup it sometimes will run 55-56 but mostly 50mph. Hit something with lower unit and it was replaced and 4 blade 21p revolution. Same setup I always had ran mid 50’s till now. Just trying to troubleshoot this problem to get back to normal.

[5keepers2]

I have the same engine. A couple of thoughts for ya: There are 2 fuel filters. 1 you change each year and 1 in fuel rail that you change every 3 years. If your engine is more than 3 years old I suggest that you change the filter in the fuel rail. That filter change is a little tough the first time. YOU DO NOT HAVE TO REMOVE COWING TO CHANGE! Go slow and think it thru and it is pretty easy!

[EuropeanAM]

Serial number 2N365563. Just like the boat is setup it sometimes will run 55-56 but mostly 50mph. Hit something with lower unit and it was replaced and 4 blade 21p revolution. Same setup I always had ran mid 50’s till now. Just trying to troubleshoot this problem to get back to normal.

Guessing that's 2B365563.

Do you have a receipt or documentation on the gearcase Part Number? Good reason for this question....

[BJ Hicks]

Yes and yes. I edited the earlier post it is 2B.

[EuropeanAM]

YOU DO NOT HAVE TO REMOVE COWING TO CHANGE! Go slow and think it thru and it is pretty easy!

LOWER cowling that is... upper definitely must come off.

BJ: Can you provide the part number of the gearcase you installed?