I have a 1990 70hp johnson I have a 14 x 13 prop on it now and can only get about 31 32 mph and it seems to use alot of fuel. I have no tach so I dont know rpm what is a good prop to start for speed. Or top mph.
What type of boat is it on? What is the maximum horsepower rating on the plate in the boat? A 13 on a 70 is usually a pontoon prop or a boat rated for much more than 70Hp.
Difficult to tell anything without rpm.
If you are running too high or too low it could damage the motor.
You could get a tiny tach. Easy to install and inexpensive.
You should also do a compression check to get an indication of the condition of your motor.
Sometimes a marina will let you use a tach and try props if you intend to buy.Is the speed by GPS?
Prop sounds too small to me but difficult to be sure without rpm.
Of course -- because you are no longer over reving the engine. If you put a 19 on it which is probably what it should have, it would be even faster. But you really need a tach to see where rpm is at.
