Won't accelerate

[Walknbob]

I recently swapped a 2005 , 50hp, onto our boat. The swap went pretty good. Except, after about 2/3 throttle it does not continue to accelerate. Moving the shifter forward causes the throttle cable to move the linkage to full extension back at the motor. But rpms no longer increase. I have not yet got the tachometer working but based on having run this motor on another boat it sounds like it is running at about 3000rpms. My first thought is that there is some safety governor but I can't find any such switch and have been unable to find an online manual to figure this out. Any thought on this? Thanks

[99yam40]

make sure the timing is advancing to spec

monitor fuel pressures to makes sure it stays in spec

make sure your prop is the correct on for your load

if you are not getting the proper voltage from key switch to tach as you may have indicated on your other thread then maybe it is not getting to some other places also

[Jason2tpa]

At the binnacle, move throttle lever to neutral. Push down the accelerator lever on the motor to full extension. Note where it stops. Now move the throttle lever at the binnacle to full extension. Note where the accelerator on the motor stops.

If there is a difference, your linkage needs to be reset. If when moving throttle lever to WOT position and the accelerator lever is at WOT position, you've ruled out a linkage problem.

[Walknbob]

At the binnacle, move throttle lever to neutral. Push down the accelerator lever on the motor to full extension. Note where it stops. Now move the throttle lever at the binnacle to full extension. Note where the accelerator on the motor stops.

If there is a difference, your linkage needs to be reset. If when moving throttle lever to WOT position and the accelerator lever is at WOT position, you've ruled out a linkage problem.

Thanks will check that out

[Walknbob]

make sure the timing is advancing to spec

monitor fuel pressures to makes sure it stays in spec

make sure your prop is the correct on for your load

if you are not getting the proper voltage from key switch to tach as you may have indicated on your other thread then maybe it is not getting to some other places also

Was thinking about fuel supply as a potential problem so will follow up on this.

[Walknbob]

Jason2tpa I checked the linkage and that seems to be ok.... while doing this I remembered that when I initially set it up the linkage was extended too far. So the first time I started the motor it sounded like it was WOT. It was only for half a second... literally as fast as I could turn the switch off. It did sound awful though. I readjusted and it then started and ran fine in the yard on a hose. It was not until it was in the water that I found the issue of not running all the way up. It starts fine and runs good up to that point. I am going to deal with the tach issue this morning and see if that changes anything.

[Jason2tpa]

So the first time I started the motor it sounded like it was WOT.

In my opinion, a good indicator of how well the engine was maintained/serviced by the previous owner are the appropriate or inappropriate adjustments made to the motor. In your case, starting the engine for the first time with the linkage set to WOT is a pretty good sign. If I were you I'd be going over that engine with a microscope to learn if there are more out of spec adjustments the previous owner made.

I readjusted and it then started and ran fine in the yard on a hose. It was not until it was in the water that I found the issue of not running all the way up.

I'm not 100% certain, but pretty sure there is a mechanical linkage difference between increasing rpms while in gear and while in neutral. If I'm correct, this is why you're experiencing a throttle difference between engine on flush or submerged.

Refer to your SM. I believe in it will describe setting the correct linkage. I know the cam roller has an arrow, or the cam lever has an arrow (or mark). Either way, the cam roller must be aligned with the mark on the lever. After you've done this, with engine off move control throttle lever to WOT (in gear). Throttle valves should be completely open. Take a look where the cam roller is on the lever. Refer to SM to confirm correct setting.

[TownsendsFJR1300]

As posted previously, being the engine is new to you, you don't know if it's properly propped for YOUR BOAT.

Click on this link, put in your info to get an idea what prop (approx) you'll need:

Outboard Performance, Performance Bulletins | Yamaha Outboards

[Walknbob]

FYI I have had this motor for 5 years just on a different boat. I have taken very good care of it. I have double checked and the linkage is correct after that initial screw-up on my part.

I have just switched out the entire throttle con*****er and it all runs great again! I had used a "new" old con*****er but it had issues with the ignition switch. After trading that out the motors runs as it should. Thanks for the input I appreciate the help and advice

[TownsendsFJR1300]

Thanks for the update, safe boating!