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70hp bogging down

H

hsp

Member
"I just had a used 70hp Johnso

"I just had a used 70hp Johnson installed on my boat. When I go to get on plane it seems to just bog down and never really rev up. Acts like it is loading up real bad. It seems to run fine in my driveway with the water hose attached.

Is the prop too much? I think it has a 19 pitch aluminum. Or does the motor need some adjustments?

Also, if I change out the prop, what pitch should I go to? It's an older 3 cylinder 70hp. Probably a 70's model.

thanks
JR"
 
"Are you sure it is running on

"Are you sure it is running on all three cylinders? A quick check of the spark plugs well let you know.
If all the plugs look ok then I'd do a compression test.
But if you can find a prop that is a 17 pitch try it. If the boat gets better then keep going lower in pitch until you find the correct prop.

There are several things that can cause this. If these few do not help let us know.

Also, running the engine in the driveway with no load means nothing. Just about any engine will sound ok without a load while running on a hose.

Not knowing where you are located(altitude)or the size of the boat makes it hard to know if the prop is to large or not.
Good luck."
 
"I have it on a 16.5 foot 1983

"I have it on a 16.5 foot 1983 KingFisher. Boat says it's rated up to 80hp.

I suspect it might be running on just 2 cylinders. I'm taking it back to the guy I purchased the motor from on Monday. I just thought I'd make a post and see if anyone else could clime in. Supposedly it tested 115, 115, 120 on the compression test before I purchased the motor.

I'm located in League City, just South of Houston Texas.

JR"
 
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