Johnson 9.9 speed results...

[12guns]

Ok, I finally did it...My 77' Johnson w/ 15 hp carb, no exhaust baffle, and open air silencer on a 1436 Duracraft "fisherman". I had my 5 gal gas tank 3/4 full, and a plastic box up front w/ some tools and such (maybe 20 lbs)...I stated w/ what I think is the original prop, 9.5x10, with the trim pin set second from the bottom, and on smooth water, it ran 23 mph fluxuating up to 23.5. The other prop was 9.25x8. It had noticably skinnier blades (possibly worn) and ran at higher rpms. Speed dropped to 21 mph. I honestly didn't expect there to be much of a difference since I lost rpms, but was pleasently supprised! The 10" pitch was smoother, and ran lower rpms which should be better on my motor. Just FYI.

 

[steelespike]

Re: Johnson 9.9 speed results...

Thanks for the update. Difficult to know where your at without the 9.9 info but
as I recall the old 10hp motors were rated at 21 mph under ideal stock conditions.
the old 18s were rated at 27 mph.The pre 89 9.9 is rated at 5,000-6,000 rpm
the 15 is rated at 5,500 to 7,000 rpm.It would seem that with careful prop selection weight reduction and trim and set up the 15 could deliver some serious speed.
Now if you raise your motor 1/4 inch at a time untill just before venting becomes a problem you may gain a little more.Be sure it continues to pump water.It would help to have a tach.

 

[12guns]

Re: Johnson 9.9 speed results...

are you refering to raising the trim or the entire motor on the transom? I assume the whole motor, but just checking. I may mess w/ it over the weekend to see what happens. It does seem to "spray" alot aroung the foot as it tracks through the water...some of which is normal, but if I can raise a bit and trim slightly, maybe it will still have power and gain some speed. Thanks

 

[steelespike]

Re: Johnson 9.9 speed results...

Yeh,raise it vertically.Just add 1/4 inch sticks on top of the transom one at a time.Depending on where your at now you could pick up a couple of mph.
Just be sure clamps still have a good grip and it pumps water.

 

[12guns]

Re: Johnson 9.9 speed results...

will do, thanks. I noticed yesterday w/ the trim bar set on second from bottom, and just my big butt in the boat, the front end would jump up and down at full speed. I trimmed down all the way and took care of it, but was hard to turn and probably too far down. Where should it normally be set?

 

[steelespike]

Re: Johnson 9.9 speed results...

Needs to be set where it doesn't bounce.Sometimes just moving the tank forward or even leaning forward is enough to stop it.As you raise it the trim setting may change.Sometimes you can buy or make a wedge to go between the clamp and transom so you can get a half a notch trim.I think you can use them in to directions to either gain half a notch or subtract 1/2 a notch net result would seem the same.If you don't want to mess with the wedges try the second notch and move stuff just enough forward to stop the bounce.