Speed & Rpm
 

Finally put her in the water today and she ran good.I am running a 2001 150 Johnson.
The tach read 4000 WOT at 35 mph.(according to GPS)The specs on the motor say 4500 to 5000 WOT.
As far as speed is concerned,and what I have read 35 mph with a 150 is about right with a V20.
I think my tach is off,what is your opinion.

RPM is low. Could need a prop change.

150 should be more like 40 mph based on my readings.

I get 38-39 but still need to tweak my motor height.

Your RPM's seem a little low.

your rpm spec should read 5500 rpm at wot, cehck your tach, tap on it next time you run the boat, see if it moves around. the boat tachs are nortoriously inaccurate, some times they stick

4500-5500 is the factory spec for WOT on that engine, but 5200-5600 will let it live a MUCH happier life. And verify the tach with a good one as tachs on outboards are VERY failure prone. ESPESCIALLY the ones that are driven off the charging system like this one is.

I agree with everybody, low speed and low rpms.
I'm scooting along at 43mph with a 14x19 prop at 5100rpms.

As a rule of thumb, every downward pitch change should get you an extra 400-600 rpm... so a 21 to a 17 sounds like it should do it.

Divide your numbers in half and your there. Every inch of pitch should equal roughly 200-300 RPM's.

The prop on her now is a Stainless 14 1/4 X 17.Need to check my tach out.I think that it may not be accurate.

I have a 2000 Johnson 150 with full fuel and (2) 225lb adults she'll do 42 mph at 5500 rpm.

That prop should be about perfect.
Does the possibility exist that the motor may need to be decarboned? Say with Seafoam or the like.
I just got through outfitting a boat for my daughter and her husband (and the grandkids) with a motor I'd had for years. When I first got the motor it would idle and run good to great but never seemed to have the top end speed I thought it should have, changing plugs, props, etc, never solved the problem. When I put it on the other boat it performed the same till I fogged the carbs a few times and started mixing Seafoam in the fuel. It is slowly improving and turning a little more rpms running wide open than what it used to.

Seafoam sounds like a good suggestion.I will give it a try.This is my first outboard,I have owned I/Os in the past.
I was pleased with the performance of the motor,other than the low RPMs.
She would jump up on plane fast.Guess you call that a good hole shot.

Besides mixing with the fuel, get a spray bottle with Seafoam in it and let the motor get to temperature and spray some in each carb throat, let it smoke and stabilize to run even and do it a few more times after that.
I would expect it will take a lot of doing this at regular intervals in order to remove enough to make a difference.
A daily outing with a good mix of the stuff should certainly help.

i