sluggish below 4k

[Ozmodius]

My MNS idols rough and is very sluggish below 4k rpms. As soon as it hits 4k its like i have a turbo on there... she becomes a rocket. Anyone ever have this?

[BrianB]

Mine idles great at about 1100 RPM and runs strong but it does get a little sluggish below 2500 to 3000 RPM. Over 3 mine becomes like a rocket all the way to red line. I have the 4 into 1 exhaust as well with stock air filter. From what I have read on here when you change from stock exhaust or stock air filter, you need to change the carb jets. Mine has stock jetting so thats why mine is like that. I just run around with the RPM's around 3000 and up.

[boyat68]

Ozmodius:

You have to synch the carbs in order to get the idle correct. If the bike is synchronized, then the pilot jets take the bike up to the 4000 mark where the mains cut in. The idle jets have to be clean as a whistle as there are very small holes in them that can get clog easily. You could also have the wrong pilots in the carbs that let too much fuel by that is bogging down the bike. You may have to pull the carbs and check everything out.

[Axel]

tuning below 4000 rpm

Synching equalizes the carbs . This is done with the 3 big screws between the carbs . Synch 3&4 ,then 1&2 then the right bank to the left bank with the screw in the middle .
Idle circuit mixture is set with the pilot screws on top of each carb . I'm sure there are many ways to do this but my fave is Colortune . A cheap tool that achieves a level of tune you will never get in a Yamaha dealer . You can actually see the color of the spark(combustion) in the cylinder as it happens with the bike running . Adjustment is done by the color - yellow for rich , blue to white for lean and absent for no combustion . 3 tests take you through idle setting ,slow acceleration and accel pump operation . Even I can do it . No ear is required other than if the bike starts to run bad - you went too lean . This operation is performed for each cylinder/carb .
After this a synch puts the icing on the cake . My favorite tool is the Carbtune . Compact ,easy to read ,no mercury, etc .
This will optimize your reponce below 4000 rpm .
Bear in mind that these bikes are no wheel burners below 4000 rpm . If your bike runs smoothly and well it may be the nature of the beast . I use these tools twice a year now and a little adjustment is required both times . Good luck

[TADracer]

How are your plugs burning? That should give you some indication.

If you have mods like pod filters or aftermarket exhaust then it is strictly jetting and adjustments in the carb area. Pilot jet, most probably. If you are still factory then I would lean toward a good cleaning and adjusting.

I am stock on the motor with pod filters and 4-1 exhaust. This required jetting up one size on the pilot jet to remove the >3000 stumble.