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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4724
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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I just replaced my 1992 90 hp Yamaha outboard with a 1986

Customer Question

I just replaced my 1992 90 hp Yamaha outboard with a 1986 115 Yamaha outboard on a 1992 17 foot Scout boat. All the wiring and cables hooked up. When first starting the motor it reved up high and had a very high idle. The motor starts and runs well. However, the 115 will not return to the slow idle stops. I have adjusted the black plastic throttle cable ends on both sides of the cable to make the cable as short as possible. It really dropped the idle. It is very close to the stops and you can easily push the throttle mechanism back to the stops. I can shift into gear but there is a slight grinding noise when the motor shifts. When swapping the motors I had to install the 115 hp black plastic throttle ends onto the 90 hp throttle cable because the hole diameter on the plastic fittings were too small.
Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
Other comments: When I bought the motor it seemed to slightly grind when shifting both in reverse and forward. The grinding noise is still there after the new installation. As stated before, making the throttle cable shorter seemed to almost bring the throttle mechanism back to the stops. However, now there is alot of dead space at the control handle before the engine starts to rev and max speed is only obtained when the handle is pushed 90 degrees from vertical neutral. My rpm gauge does not work. How do I reduce my idle speed to prevent grinding? The motor starts immediately and looks brand new.
Expert:  Jeff G. replied 1 year ago.

The cable ends are the same 1986 or 1992.

Thread the cable ends onto the control box end 8mm. The engine side is then adjusted to fit the throttle.

You really need a tach to determine the idle speed and wide open throttle speed. Without seeing the engine I can't see how close the adjustment is.

Keep in mind the engine will run faster at idle out of the water on the flushing devise.

Remove the throttle cable from the engine, push the throttle linkage against the stop. Now either by hand or the control shift into gear. See if you get the same amount of grinding. If it does it in the water then the problem is in the lower unit. The shifter may be worn.

Let me know how it does.Any additional questions let me know.

Customer: replied 1 year ago.
I hope to follow your advise today.
Expert:  Jeff G. replied 1 year ago.

Post back your outcome. Thanks

Customer: replied 1 year ago.
As soon as I get the boat in the water I'll respond back. Thanks again. Ted
Expert:  Jeff G. replied 1 year ago.

Thank you Ted.

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