15hp johnson plane 16'er

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muddywaders

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Recently mounted an old johnson 15hp on a 16' welded skiff for the purpose of tuning it before I sell it.
Got the motor to run smoothly, however wont get completely on plane.The boat weighs approx. 300 lbs.
and is totally flat and 60"wide.The motor revs out with a 10" prop and doesnt seem like its slipping(hub) but wont flatten
out even when i tried removing the trim pin and moving fuel tank to bow.When the motor was on a 13' fibreglass
it planed two it planed two men easily.The Skiff pops onto plane instantly with a 20hp merc. and feel the johnson15
should plane with just me in the boat.?????
 
On the Johnson it would depend on the year etc. The Hi speed jet, the old ones were adjustable, is where your problem lies.
Maybe the float is set too low, but mor'n likely it's the Hi Speed jet not letting enough fuel through.
 
What these guys are saying is that the 16' welded hull is most likely a 20" transom boat.
Your "old" 15hp engine is most likely a 15" shaft engine.
If this is the case then this is the reason the engine just "revs out" instead of pushing the boat on plane.
All the prop is doing is picking up air when the bow starts to drop over on plane.
 
Shortshaft on a 15" transom.Prop is not ventalating and in good shape.Had this setup out the other day did get it to plane but the hull would not completely flatten out.The motor accellerates well and feels like its has good compression.Can only judge rpm at wot by ear as I do not have a tach for it.Wondering if anyone has tried 15 horses on a similar hull with success possibly a newer motor.Maybe a 15hp would be sufficient on a16'x48" whereas a hull 12" wider
would not?
 
How old is old, 50's, 70"s? You will probably need to drop to a 8 or 9 pitch on the prop. That motor can run at 6000rpm's all day if it is a 1974 or newer.
 
If it planes out but still runs bow high then try and place your "moveable" weight as far forward as possible.
taking if for granted here that you have your trim pin adjusted as close to the transom as possible??
That engine has plenty of punch, specially compared to the new engines.
You may need to go to the propeller for the 9.9hp to get what you need out of it.
 

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