johnson 9.5 won't get on plane

[USCFisher]

well first off, i recently restored my grandfathers old 1959 model F Alumacraft (14' aluminum v hull). i also purchased a 1973 johnson 9.5hp outboard from a friend for very cheap just to get me by for the time being. the problem that i'm having is that the boat doesn't seem like it wants to plane off. i've had the motor inspected by a friend (who's a small engine mechanic)...we rebuilt the carb already (which was very clean) and the compression is good. both cylinders are getting spark and it hasn't fouled any plugs at this point. as far as weight is concerned we're looking around 600lbs. (it's rated for 660lbs) with motor, gear, gas, and 2 small adults. i do not have a tachometer on the boat so i'm not sure of RPM but the motor does not seem to be revving very high when running WOT. also, from looking at the prop on the motor now, i would say that it's a 8 1/4" x 8p (or 9p) but that's just an eyeball assumption. does anyone have any suggestions on what i can do to help plane this boat off? i'm thinking a prop in the 8"x7p range would probably get the RPMs up slightly to help hole shot. any advice would be appreciated. thanks.

 

[steelespike]

Re: johnson 9.5 won't get on plane

I think the standard prop is 8 1/4 X 8.Number is usually on the prop.
I my opinion the 9.5 should plane that load.Probably 16-18 mph.
Check for full throttle,Check the kink and sync.Check that both plugs are firing by carefully pulling one plug wire at a time.
See if it responds to a little choke.Try different trim settings.
If all else fails perhaps a 7" pitch.

 

[USCFisher]

Re: johnson 9.5 won't get on plane

so i just got around to pulling the prop off yesterday and it's a 8"x7" so no wonder why it's not planing off....i've ordered a 8 1/4"x8" prop so it should be here next week. i replaced the spark plugs and go figure, the previous owner had installed the wrong plugs. it runs 10 times better now....almost even planes out. hopefully the new prop will get it up and going like it should be running. i'll be sure to post my outcome. thanks for all the help.

 

[steelespike]

Re: johnson 9.5 won't get on plane

If the motor doesn't seem to be winding up now I think yoiu may be dissapointed with the 8.Going to an 8 will lower rpm by ABOUT 400.
If it won't plane with the 7 it isn't likely to plane with the 8 unless the 7 is damaged.Motor trim and weight placement are critical.
Eliminate as much weight as possible.Go to a 3 gallon plastic tank.
place it in the middle or at the bow.Go to a light weight Danforth style anchor.cans instead of bottles etc.You may need to move weight to the bow just don't over load there.
A few pounds can be the difference in planing or not.