Help with a funny engine noise.

[Jim Hawkins]

Working on a friends motor, Yamaha 1999 50HP. Starting the motor without any throttle the motor runs at higher than normal RPMs for a few seconds, then calms down to a regular idle after which it sputters, emits a Loud squeak sound like a sneaker on linoleum and stalls. It will do this for 3 or 4 starts until it stays running.
What would do this???

 

[mike_i]

can you post a video?

 

[Jim Hawkins]

can you post a video?

No but I found a video on youtube with the exact problem and they said it was lean carbs. Adjusting the screw doesn't help so looks like a carb cleaning is needed

 

[Jim Hawkins]

OK so no luck here and I'm back to pick brains,

Rebuilt all 3 carbs and adjusted them all from 2 and 1/4 turns out to 3 turns as recommended by many with the same motor.

Didn't help. Runs just like before. In trying to readjust all the screws I found that the bottom carb is the only one that made the engine do the lean sneeze. I ended up with the top 2 carbs set at 1 and 1/2 turns out and the bottom at 3 but it still sneezes when starting.

I'm wondering if it may be an adjustment in the controls in the picture.

Note* the top arrow and the right arrow both point to adjustments where there is a line that seems to be for calibrating and both seem slightly off

 

[Jim Hawkins]

This just in...

So, I questioned the control linkage because when I re-attached the linkage to all 3 carbs after snapping on to the bottom carb, the top two needed the butterfly opened slightly for the linkage to line up. So, after trying different adjustments I pried the roller off the arm that meets the throttle cam (arrow #2). This allowed the bottom carb butterfly to fully close and the carb linkage to line up with all 3 carbs. I got a fairly regular start with no stall and no sneeze.

WTF?

 

[99yam40]

every time the carbs are put back on you need to follow the link and sync procedures in the service manual.
it includes carb and timing linkages and the roller.
get a manual and follow it

 

[Jim Hawkins]

every time the carbs are put back on you need to follow the link and sync procedures in the service manual.
it includes carb and timing linkages and the roller.
get a manual and follow it

THANK YOU!

I took what you said, did a search and found a YouTube video that takes me through the whole process.

I hope it's OK to post the link on here but anyway, here it is.

 

[99yam40]

get the manual and follow it this guy is not following it.
you should sync the carbs together with all of the butterfly valves completely closed which he never did.
setting the linkage and timing should be verified with a timing light .
also need to make sure on the roller position (timing pick up)when all done