Prop size for Johnson 70 hp

[Nelsgt]

Just did a rebuilt on my 1981 Johnson 70hp power head, Motor had a 13x19 prop on it and it is pushing a 16 ft Glasply. Motor is rated for 5500 rpm wot and I am getting 4200 rpm wot... Carbs were rebuilt and seem to be operating correctly, I am wondering if this to much prop? And what kind of top end speed should I be expecting? Thx T

 

[Haffiman]

Re: Prop size for Johnson 70 hp

You are about 1000RPM LOW!
First verify your tach that it reads correct.
If an original tack, take a small screwdriver and 'twist' the adjustment at the back a couple of times, then back to '6'.
Then try to verify with another tach.