Can't quite get the jetting right on the XR600

I have made a few mods to my 98' Xr600, ie FMF Powercore 4 pipe, snorkel removed etc and I've tried various jet setups and at the moment the 158/68 seems to work pretty well but when your let off the gas it hesitates and continues revving for a second before dropping down.

Does this mean the mj might be a bit too big?

I am currently running the same set-up-68S pilot & 158MJ, and before I lost 4th gear-the jetting seemed to be perfect. I am going to step up to a 160 MJ after I repair the trans just to see what happens. Where is your needle set-which clip position? What type of air cleaner?

needle in 3rd clip and stock air filter.

Does this mean the mj might be a bit too big?

Yes, this usually is what it means. Try a 155 and see of it helps any. Get a jet from the same mfg as made the 158 that you have now. There can be differences between jets with the same number, but from different mfgs.

You have to get rid of the stock filter and backfire screen as well.

I would say to change the air filter BEFORE you change the jet again! If it is running just a tad rich right now, going with a UNI filter will lean it out a little bit.

Purchase/install a UNI air filter, then see if the problem goes away. I have the UNI, and with the same MJ, I am NOT rich. My spark plug after a full throttle run is a nice caramel color.

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