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Author Topic:   Yamaha 90
Jay Herrin posted 04-02-2002 08:15 AM ET (US)   Profile for Jay Herrin   Send Email to Jay Herrin  
Probably a dumb question....At about 1000-1200 RPM's my Yamaha 90 seems to run a little rough. Dealer says its normal, but other engines are smoother in this range. Very smooth below 1000 and above 1200-1300. Could I have 1 jet stopped up? Is there a way to tell? My area has a lot of Manatee zones and this is the speed I go quite a bit of the time. Any suggestions would be appreciated. Thanks, Jay Herrin
JohnAz posted 04-02-2002 08:25 AM ET (US)     Profile for JohnAz  Send Email to JohnAz     
Manatees go well with Mashed Potatoes
Bigshot posted 04-02-2002 10:59 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
3cyls will do that. You are probably between the low speed jets and kicking in the highs so it is confused. Bump up the throttle a bit and trim it down all the way and your wake should be the same.
Salmon Tub posted 04-03-2002 10:08 AM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Ya, I had same problem with my Nissan 90 3cyl. 5 MPH zones are killers. I fiddled with the mixture screws a bit (actually, a lot - many hours wasted to get them just right.) and am happier now, still a little rough. Seems to smooth out at about 8 MPH. This speed is crucial, as it is the trolling speed for Albacore +/- a little.
masbama posted 04-03-2002 11:07 PM ET (US)     Profile for masbama  Send Email to masbama     
My 3 three cylinder Johnson did the exact same thing. I spent a lot of time trying to fix something that was not broke. It's just the way 3 cylinders are.
Clark Roberts posted 04-04-2002 07:47 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Re: 3cyl carb adjustments...try this: Screw in the low speed idle/air needle valve (check manual for location...should be obvious) on each carb clockwise until it lightly seats and then back out 1 1/2 turns. Now, with engine warmed up, idling in gear, tied to dock... turn clockwise (lean) until engine begins to stall and then back out ccw until it starts to stall (rich). Then try to adjust to midpoint (a little on the rich side if in doubt). Same for each of the three carbs. Adjust to idle rpm per mfg recommendations usually 7-900 rpm. Merc idle is varied by timing only and Yam has a throttle arm stop on one of the carbs... OMC? it has been so long that I forget! There is a lot of "fiddle factor" involved here and the final adjustment can be wildly varied between the carbs. What I try to do is get rid of that annoying "caugh" at idle. It is important to make carb/idle adjustments with engine in water since the height of the water in the midsection determines backpressure and on a hose there is no back pressure..etc..etc...etc... blah.. blah.. gee I try to make my posts short and simple but can't quite get the hang of it! Happy Whalin'.. Clark

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