Low Vacuum

[PatrickM]

2003 F90TLRB is running rough at low speed below 3k rpm. After doing the usual, fuel, plugs, compression check, etc., attempted to sync carbs. The reference carb #4 only draws 9 in Hg max and is not adjustable as far as I know. Setting the other 3 carbs to the same reading smooths the idle out somewhat but there is still an occasional cough while idling and hesitation when advancing to WOT. The manual does not give a spec for vacuum value, only vacuum difference from one carb to the other.

Does anyone know what the normal vacuum reading is for the reference carb?

[boats.net]

Probably need to remove and clean carbs and check intake gaskets, it's running too lean.

[almetelo]

sometimes needs more than one time to clean carbs properly

[PatrickM]

Thanks fellas, that was my assessment as well. I'll make an appointment with a Yamaha dealer to do the carb cleaning since they have the experience & tools to the job correctly. HOPEFULLY!