My motor is on a 20foot Pontoon Barge.
I've had starting problems since new. Start-stop-start,-when finally starts it is OK
Dealer removed the antisiphon valve from the gas tank that was supposed to help, it didn't.
I replaced all of the hoses, the 20 micron fuel filter, bulb and re-reouted fuel lines to allow a smoother flow of fuel and checked compression on all three, 115# on each. Which is good.
I purchased a Yamaha manual and a Clymer manual(my opinion it is a better choice) and verified that all of the carb and timing settings were correct and they were. I did set the idle alittle higher though.
So now I'm on bulb 3 or four, can't remember.
Now when starting the Prime Start kicks in, RPM rises (1500 0r so)for awhile then drops to Idle RPM (about 900)like it is supposed to.
I'm stumped The latest bulb that I purchased was for another engine (Evinrude) and I didn't use it, but seems to work great ????
I just purchased another spare (Wal Mart) in case.
Now if I leave the boat sit for awhile the bulb seems to be full, a gentle squeese and it is hard.
I'm still confused ????---But it is working.
Lastly, you can't adjust those carbs- they are plugged & sealed, no adjustments possible.Only the opening and Synchronization of the three..
Just a suggestion, you can check the fuel filter on the engine for precipates from alcholol in the fuel. it might be causing a stoppage.
Here in arkansas they recommend using the Yamaha 20 micron filter to filter out the water in the alcholol laden fuel.
Let us know what fixes it.