low power

[boater55]

i just got a 1969 Johnson 9.5 hp outboard for my 12 ft seaking boat, i bought this to replace a 1953 brooklure i had on the boat because i wanted a newer motor and more power i expected to double the speed but it did not the 5 hp motor made the boat go 6 mph and the 9.5 hp made it go 10 mph in W.O.T. i was expecting allot more power then it is giving, i know both cylinders are firing and it has great compression does anyone know what the problem might be? or is this all i can expect from this motor? i was also considering hydrofoil would this make a difference? i would also appreciate tips on trim adjustment and lean rich fuel adjustment for maximum speed
Thank You

 

[ultra353]

Make sure the spark will consistantly jump a 1/4'' gap with a bright blue snap, do a compression check, those carbs are known for getting the high speed jet clogged because the jet sits horizontally so clean carb.

 

[JMichael]

Besides the bare boat hull, motor, and fuel tank, how much additional weight (people, gear, batteries, etc) are you pushing in the boat?

 

[boater55]

Besides the bare boat hull, motor, and fuel tank, how much additional weight (people, gear, batteries, etc) are you pushing in the boat?

there is me (145 lbs)
my brother (165 lbs)
fishing tackle and tools (40 lbs)
and it has casting seats with a indoor/out door carpeted floor board (i don't know the weight)

 

[krawler]

Here are some other things to try.
Pull the flywheel and clean/reset the points.
Check to see if the coils are cracked. Replace if they are.
Engine off, put in gear and rotate to full throttle: is the timing plate up against the stop, is the carb. fully opened.
What does the prop look like. Is it the stock plastic prop.
Where does the motor sit. Anti-cavitation plate even with the bottom of the boat or is it much lower.

The Johnson/Evinrude 9.5 is not a high output motor. With today's gas, your lucky to get 7.5 horse power out of it. That motor with a perfect prop and running at its best, you could expect somewhere around 13 to 16 mph. On a boat with a square chine and no weight maybe 20 mph.

One other thing you could do is sell that motor and buy a Johnson/Evinrude 9.9

1964-1973 Johnson/Evinrude 9.5hp is basically a 7.5hp with a bigger carburetor.
1974-current Johnson/Evinrude 9.9 is a 15hp detuned with a smaller carburetor.

 

[Pappy]

Since you never mentioned any running quality issues with the engine I would hesitate before going and checking all the things that have been mentioned.
If you have weight to move around.........move it and see what results you get.
Look at your propeller and see how badly worn it is. May need a prop with full blade area and not bent up.
Do you have a 20" engine on a 15" transom?

 

[bbstacker1]

I've never had one of the 9.5's (just not my thing) but from what I've heard they are not overly powerful. I am thinking you were hoping for more than you will ever get from that motor.

 

[rickybobbybend]

I think there is more to be had from that motor. I have a 12 footer/9.9 'Rude and with me and gear aboard (total weight including hull and motor is about 465 lbs.) it clocks a shade over 20 mph (GPS). I agree with Pappy, play with weight distribution and look at the motor, starting with simple stuff like the prop.

 

[boater55]

the prop is good i re distributed the weight and bought new spark plugs i just ordered a carb rebuild kit
i was thinking about getting hydrofoil would that be a good idea?

 

[JMichael]

From everything I've read/heard about hydrofoils/whalestail, they generally help a boat get up on plane faster but at the cost of reducing top speed, because of the added drag they create.

 

[ultra353]

I agree on the 9.5 not being a powerhouse. But make sure the motor is running correctly. I`ve had a couple of 9.5`s , one on a shallow 12 ft with a casting deck and gear that would push myself and 9 yr old at 12-14 mph on a calm day. any headwind it would knock it down 2-4 mph. The other 9.5 that i just went through-carb/ignition/pump/lower seals was put on my 14`6 ft -67'' beam deep v with decks and gear with 2 adults/ 2 kids probably didn`t get above 6-7 mph. Just some idea on performance, although every boat is different.

 

[Andrew04]

This is very wierd as my first motor was a 54 Sea-King 5 horse (same thing as your brooklure) it went 6 mph once i got it running perfectly. This wasn't enough so I found my 1970 Johnson 9.5. After rebuilding the carb i've achieved 11mph.

I have heard these are basically 7.5 horse blocks with tweeking, either way mine is pretty darn bullet proof after the simple maintainence I've done.

If our next motors line up too, I'll be creeped out.

 

[Johny25]

You are asking too much from this motor and there are far to many unknown variables in this equation to point the finger at the engine as someone else pointed out above. Factor in weight (of everything), prop size, hull design and weight distribution and you can reach any number of outcomes with performance and 10mph is not bad for a 69' 9.5hp that was rated at the CRANK not prop.

My math says your pushing 600lbs plus on a narrow hull design (assuming, since most 12' are narrow typically) so 10mph is right on the money with that size and year motor. Sure you can re prop and shift weight to gain a few mph but to think you will ever see 15-20mph with that setup is HIGHLY unlikely if not impossible.

I would say NO to a whale tale and save the money for a bigger/better engine if you want to see speed numbers in the teens

 

[boater55]

thank you all for your help!

 

[boater55]

i found out i have a 8x8 propeller does anyone have any suggestions for a beater propeller for achieving top speeds?

 

[Johny25]

Higher pitch equals higher speeds....... if your motor can turn it. If you do not know what RPM you are running with the 8 pitch then there is no way of telling if your motor can turn a 9 or 10 with the setup you have. If I remember correct you are running a pretty heavy setup already so I doubt going up in pitch will help you, and it most likely will hurt you.