150 Hp, Prop/lower unit replaced, now problems

[wjj]

I know this topic may have been beat to death here, so I have spent an hour searching, but still don't have the right answer.

I have a 1994 Robalo 1820 CC with a Merc. 150.

My lower unit went out a few months ago, and I had the lower unit and prop "replaced". Instead of rebuilding the lower unit I had, the mechanic I used told me he had a lower unit that fit. Because of this and other issues, I no longer trust this mechanic.

I didn't use the boat except for idling around the neighborhood canals during the winter, and I have now begun using it as the weather is warming up.

But, the boat no longer comes out of the hole as it did before, and with more than one person it takes a long time to get onto a plane. Three people on the boat, and to plane two have to be on the bow.

Motor seems to run fine, no roughness, starts right up.

Prop size?? Lower gear ratio?? Both?? How do I check, where do I look??

 

[CharlieB]

Re: 150 Hp, Prop/lower unit replaced, now problems

Trim the motor up out of the water and make a chalk mark/line on the prop and gearcase.

Pull the sparkplugs, shift into forward and chalkmark the flywheel also. Now start turning the flywheel and counting the number of turns it takes until the prop and gearcase marks line up again. This will tell you the gearratio of this lower unit.

Repost this number and the original model and serial of your motor, someone will look it up and then we will know how much it has changed.

What prop is on now and what was your original prop?

What was your original WOT RPM and what can you get out of it now with your current prop?

Knowing all of these is necessary before making any recommendations?

 

[wjj]

Re: 150 Hp, Prop/lower unit replaced, now problems

Thanks for the info, I will do what you say and will reply.

Wayne