Carb butterflies not opening all the way on full forward throttle

[Blue Man]

I just repowered from an 86 yamaha 90 hp 2 stroke to an 87 yamaha 115 hp 2 stroke. I expected the boat to perform well but it is actually slower. I initially thought it might be the prop but I noticed the butterflies don't open all the way at full throttle forward (instead of being at 90 degrees they're at about 65 degrees). The strange thing is the butterflies do open all the way at full reverse throttle.

I did not swap out the Yamaha controls or cables. Any idea what could be going wrong? Everything worked fine on the old motor.

The guy I bought the motor from thought it was probably a Yamaha controls problem but I'm not sure where to start.I am certain that the carbs are perfectly clean though..

Thanks for your help.

 

[gm280]

You need to see what is holding them form opening. If it is linkage, then you need to readjust it or find new linkage that will allow it to operate properly. Check your throttle cable from the controls at the helm. Make certain they are operating to the fullest extent. Also check to see if you have any adjustments at the engine with the throttle cable. Could be all you need is some simple adjustments. JMHO

 

[Blue Man]

OK thank gm250. I'll give it a try.

 

[gm280]

OK thank gm250. I'll give it a try.

Let us know what you find. That way others can learn as well. JMHO

 

[Blue Man]

OK, so I figured out the problem. First I had previously reversed the forward/reverse and flipped my Yamaha 704 binnacle control to give me a few extra inches away from the steering wheel. The old motor had less range of motion in the throttle so I never had a problem, but the new motor has more range of motion in the throttle. The original controls are set up to not allow you to go full throttle in reverse. Since I reversed the throttle control and it wasn't an issue on the old motor, I didn't know the limiter existed in the remote throttle control.

The fix was a simple as reversing two external screws in the exterior of the Yamaha 704 controls and I now have full throttle in forward gear and partial throttle in reverse. Thanks everyone for your assistance.

 

[gm280]

OK, so I figured out the problem. First I had previously reversed the forward/reverse and flipped my Yamaha 704 binnacle control to give me a few extra inches away from the steering wheel. The old motor had less range of motion in the throttle so I never had a problem, but the new motor has more range of motion in the throttle. The original controls are set up to not allow you to go full throttle in reverse. Since I reversed the throttle control and it wasn't an issue on the old motor, I didn't know the limiter existed in the remote throttle control.

The fix was a simple as reversing two external screws in the exterior of the Yamaha 704 controls and I now have full throttle in forward gear and partial throttle in reverse. Thanks everyone for your assistance.

Okay, you figured it out and fixed it. Congratulations! And thanks for posting what the problem was and your fix. That way other will learn from your repair. That is what makes these forums the best. :thumb: :thumb: