Johnson performance

[THEFERMANATOR]

Originally Posted by Mulv80

My 2000 Johnson 150 would run 42 mph at 5500 rpm on my 79' V-20.

His old crossflow isn't going to run quite as strong as a newer looper. He should be turning up to about 5300RPM's WOT and I would think high 30's to maybe 40 is possible if all is right with it.

[jasoncooperpcola]

I am beginning to believe this big *** prop is my trouble. The 15x17 i found for $40 was sold before i could call. Based on what i have read through here i am leaning towards a 14.5x17 prop. Right now i am swinging a 15.5x14 and also have a 15.5x15 aluminum (spare) that does even worse.

I put my throttle wide open, and yes, all carbs are wide open. So my issue is not there i believe. I was able to run it on the hose and use the rest of my sea foam out of my 6 gallon tank that i couldn't use when running.

The previous owners have put some money into this motor. She cranks within two seconds now. Also what should my compression be?

[tsubaki]

I ain't got no idea what the correct compression should be but I'd tend to believe 90psi and above should be good. And hope for less than 10% difference between the cylinders.

Have you tried to reposition the engine up a hole or two?
I'm guessing about 3/4" above the bottom of the boat (cavitation plate) should be close.

[jasoncooperpcola]

Right now my cavitation plate is level, maybe a hair lower, than the keel. I will set up a scaffold frame tomorrow and lift her up. How many holes? Right now the top bolt is in the 2nd hole from the top.

[tsubaki]

You can do it easier by using the skeg of the motor (with a board under it)
and the trailer tongue jack.
With the engine tilted down, place the board under the skeg and then crank the tongue jack till the skeg contacts the board.
Loosen the bottom engine mounting bolts then remove the upper bolts.
Crank the tongue jack up till the desired hole is reached. Reseal and rebolt the engine.
I'd level the cavitation plate with the bottom of the boat. Then measure to find out how much or many holes to be about 3/4" above the bottom of the boat with the cavitation plate.
That should give you a good starting point.

Keep in mind, on most boats the cavitation plate being level with the bottom of the boat is the normal starting point to see where the best location is. These V's have a pretty steep angle and may need to be a little higher than others.
There are other factors that will contradict this method but it's a starting point.

[jasoncooperpcola]

When running it the other day, i noticed the water was 2-3 inches above the cavitation plate. But that was with the doel-fins on. I took them off for another run and forgot to check how the water was coming out.

I like your idea tsubaki. That is probably how i will do it.

FYI top end and rpms didn't change with the doel fins on or off. The only thing i noticed was in turns the boat was more stable with the doel fins.

[tsubaki]

Every engine we ever came across that had those things on them we took them off.
I'd say 90% of the time most of the problems can be fixed without them by proper weight balance in the boat and correct engine height.
Why don't they come on engines to begin with?

Remember, loosen the bottom bolts. Don't remove them.
Just enough to let the engine slide on the transom.