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I’ve been dinking around with jetting for almost a year now, and I can’t seem to get it right. I have a 05 660R with a RS-3 Yoshi Complete system, proflow kit with K&N filter, and running with no lid. My jets are Mikuni 162.5/160 main, 27.5pilot, 3rd clip on the needle, 2.5 turns on the air/fuel screw. I live on the Oregon coast so it’s cool, humid, and at sea level.

What my problem is that I’m fine through the bottom and middle range, but when I’m running full throttle in top gear, I have seem to have good acceleration and then it suddenly falls off and sputters a little.

I was thinking maybe it was on the rich side so I put in a 155/160 main (Yoshi's suggested jetting). When I do this I completely loose the mid range and run lean; unless I put the airbox lid back on, then I don’t have any top end (rich?).

One thing I’m considering might be the problem is the Rev Limiter. Could that account for the fall off in full throttle with my first jet settings?
 

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Stock cam? I know mine will fall off because of the cam well before I hit the rev limiter.

Sorry don't know jetting well enough to offer any advice.

Welcome to the forum.
 

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I can't imagine that you're hitting the rev limiter topped out in 5th gear on a raptor 660. It doesn't kick in till at or above 9k rpms and there's just not enough power to do it. Even if you're geared way down and holding it for miles at a time it'd still be a pretty big stretch to believe that the limiter was your problem.

Either your carbs aren't sealed properly (needle seats), your carbs are dirty, your airfilter/path is obstructed or improperly sealed or your jetting is off. If you're going to change jetting I'd be bumping up not down.
 

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sound like you actually might be a little lean. try dropping the needle one clip and tell us how she feels.

it sounds like you have stock needles like i did for a long time. i said i don't need needles, mains and pilots should do. and it worked fine until i put a full exhaust and removed the airbox. i messed with the jetting for a really long time like your self and finally broke down and bought some needles. since i had a lot of mains and didn't want to buy a whole kit i bought the needles by themselves from rsp. wow now i can really "feel" what main jet works.

http://gallery.bcentral.com/GID4990802P3628922-Yamaha/Raptor/Carb-Needles-for-your-Raptor.aspx
 

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I've got the identical setup as you with the exception of the pilot jets....I have size 25, and mine does the same thing as you're describing. I'm going to try to move the clips on the needles down, and maybe turn screws out 3 instead of 2.5. I'm at sea level as well...if i figure it out, I'll let you know....and you do the same for me.
 
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