First mods, what do you think?

Just bought a X650L, my first bike, and have put a thousand miles on it. Now I can't stop thinking about modifying it.

Last weekend I took off all the smog stuff. It was very easy and I like being able to see the engine now. The next step is to do the air filter, snorkel, jetting, and exhaust. Let me know if this is a good plan:

First, it sounds like you have to rejet if you change the intake or exhaust so I plan to do all of this in one sitting. So I will start by removing the snorkel (can't be hard, right?) and installing a Uni filter.

Next I will disassemble the carb, replace the pilot and main jet, grind off the tab on the mixture screw, add a washer, grind down the slosh baffle, drill out the slide and put it back together again.

Finally I will remove the baffle from the stock exhaust.


Everyone says you have to rejet if you change the exhaust or intake. However most people seem to run a 26 series 55 pilot (part no. is N424-26-055) and a 158 main jet (#99101-393-158) no matter what exhaust they are using. Is the intake more important than the exhaust?

I don't really understand what I'm supposed to do to the slosh baffle.

I have heard people mention removing the baffle from the exhaust but I don't really know what that means. Looking in the end of the pipe, I notice two screws and a couple little tack welds. Is that the spark arrestor? Should I drill it out with a 2" drill or cut the welds, unscrew it, look for something that looks like a baffle, cut it off and then replace the arrestor?

Any and all comments much appreciated.


In no real order:

-You only have to diddle with the slosh baffle if you end up with the long pilot jet

-55/158 seems to be a very good combo with the stock exhaust

-58/158 has been reported to work well with a non-stock muffler

-the best jetting with an aftermarket pipe seems to vary

-the best jetting can only be determined by trying different combos- small differences (thickness of the washer, for example) can make the best jetting on any 2 bikes different.

-for me, good manners and predictability are more important than peak power, so I tend to run a touch rich.

-to get the baffle out of the muffler, grind the 2 welds, pull the bolts, pull the baffle.

-the baffle is not the spark arrestor. the SA is still in place if you pull the baffle

I'd run the 55/158 with the baffle in, if its a touch rich then that'll prob. work well with the baffle out. If stealth is important, leave the baffle in or make a turn-down to replace the baffle. Some people shorten the baffle as well.

If your part of MA uses gasohol, you need to go richer. CT switched to gasohol when I lived there and it was tough to get the jetting right.


As long as you use the short pilot jet which is the 26 series you have listed you do nothing with the slosh baffel. Just put it back in place.

Great list of Keihin jets

Thanks for your advice. Very useful stuff.

When adjusting the jetting, what are the variables? It seems like the coarse ones are the main and pilot jet, then the mixture screw affects the idle but you can also adjust the washer thickness?

It seems like much of this is done by listening to the bike and looking at the spark plug. How else do you determine proper jetting, would finding someone with a dyno be whorthwhile or just expensive?

Worst part about dynoing it to find the right combo is how much of a pain it is to swap jets.

Allen screws on the bowl and de-smodded it still takes me 45mins-hr to swap main&pilot jets!


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