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Author Topic:   Yamaha 90 carb adjustment
Popeye posted 11-20-2002 10:16 PM ET (US)   Profile for Popeye   Send Email to Popeye  
1997 Yam 90. The Sealoc manual shows the pilot air screw as being 1.25 inches out. It lists this for the middle carb, the top and bottom are blank. It must be for all three, right? Trying to smooth the idle a bit. I have been told that a three inline wont idle as smooth a v-4, any truth to that?


Clark Roberts posted 11-21-2002 06:27 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Pop, each carb has idle/air adjustment needle valve (screw type)! I think you mean 1.25 turns (not inches) for initial adjustment which allows starting of the engine. Turning valve clockwise (CW) will lean the mixture (less gas) and counter CW (CCW) will richen (more gas)! Start with any carb and turn CW until engine runs rough, then back off CCW until same and then try to adjust to about midway or smoothest (a little richer is better than a little leaner). Repeat for the other two carbs! Oh yes, best for adjustments to be made with boat in water and in gear! Happy Whalin! Clark... SCN
Popeye posted 11-21-2002 10:38 AM ET (US)     Profile for Popeye  Send Email to Popeye     

Thanks Clark,
That is pretty much the way I had it figured. Need to get my hands on a factory manual. Put the motor in a 200 gal. rubber live stock watering tank and have it running fairly smooth now. Sure beats doing it at the ramp, having to deal with boat wakes and such.
Thanks Again,
Steve Leone posted 11-24-2002 01:01 AM ET (US)     Profile for Steve Leone  Send Email to Steve Leone     
As gas tends to run downhill it is advisable to have the top carb slightly richer, the bottom carb slightly leaner, the middle carb in between. This can smoth your engine out considerably. Steve
weekendwarrior posted 12-04-2002 10:48 AM ET (US)     Profile for weekendwarrior  Send Email to weekendwarrior     
Be careful that you have the fuel screw and not the AIR screw. All carbs are not the same. If it's a fuel screw then out will be richer and in will be leaner. If it's an AIR screw then it would likely be out for leaner (more air) and in for richer (less air).

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