1990 60hp johnston motor

[vegasss]

Hi,

I am posting this for my father, he has a 1990 60hp johnston motor and it slams/jumps when he runs it over 10mph

he has paid over 1600.00 to 2 different delers and they can't figure it out.

he has had them
replace
3 coils
fuel lines
primer
plugs
wires
timing
sync the carbs
rebuilt top carb

it idles fine it trolls fine but after 10mph still shutters everytime

[Black Swan]

Could be a worn / damaged clutch dog.

[gonzo]

I believe that mechanics should be responsible for their troubleshooting. We never charge for doing something if it doesn't fix the problem. Whoever does is a crook. Your mechanic should take care of the problem at no charge. Have you considered small claims court? A bad clutch dog could be causing it. If they had tested the motor after the "repairs" it would have shown the problem was still there. I suggest you get it back to the shop and insist they test it with a dyno or a test wheel. If they don't have that, they are not equipped to work on outboards.

[pungolee]

A bad clutch dog would be my first guess.A bad prop would be my second.I have also had this experience from cavitation,brand new boat and motor package.If the dealer does in fact clear the lower unit and prop as fine you may have a hull problem.Motor set too high?Deep keel/worm strip?Wrong size prop?Does your hull have trim tabs,if it does,they may be set at wrong angle or damaged,if it doesn't,it may need them.Does your motor have a "Doelfin"type wing on the lower unit?This may help.Get the bottom end cleared and go from there.