I have a 2006 with all the free mods, but could use some more power. I have the stock muffler and header. I have a brand new FSW header the PO gave me, but no muffler to go with it. How much power gain would I get if I got an aftermarket muffler for this header and and installed them? Would it be a big or small change?

 

I would guess it would be a big change, since many folks either went full system or just slip on for that bike. The stock can is pretty restrictive, the header isn't too bad though.

Perhaps you could sell the header and buy a slip on with it?

 

Big.
Do both.

 

A new muffler (a.k.a a slip-on) is going to be the biggest Dollar-per-HP performance increase you'll get I believe. HOWEVER - you will also need to change the jetting on your carb to handle the extra breathing the engine is afforded by a less restrictive exhaust system, so factor that little cost in too.

 

i disagree, i ran my bike with a 2bros slip on for the first 4000 miles of owning the bike without touching the carb. and it ran great. u do get more power by doin the jetkit but i dont believe u "need" to get a jet kit immediatley.

 

Wouldn't this cause the big to run even more lean than factory settings, ie causing damage to the motor in the long run? I'm new to my 09 KLX 250S and only have experience with EFI tuning, so correct me if I'm wrong. More air in and out normally means you need to add more fuel. I guess what I'm asking is what mods can you do to the 09+ KLX250S and safely not rejet it, ie uni filter/slip on. What 2bros slip on do you recommend?

 

you can run stock jetting with almost any slipon and still have decnt run quality. But if you also open up the intake by removing or enlarging the snorkle and going to a free'r flowing filter, then you could be lean. Or at least you'd be leaving alot of performance opn the table.

With the stock cork intake snorkle in the box you FORCE the small stock main jet to pull fuel, much like a choke plate on a carb does. Uncorked you lose alittle of this choke effect and compansate with a bigger jet. Added bonus if the engine revs more quickly and more freely. If you bike doesn't pull strong to redline in lower gears, you've left a little on the table, but it can still run OK. At 250cc I think the stock head,pipe is fine, it's the muffler that is the cork.

 

If you're not opening up your air intake and rejetting, I don't think your getting the value out of your aftermarket exhaust setup. To me that's just a waste, and since jetting can be as inexpensive as you want it to be (just buying the proper jets you want, or going DJ Kit) I don't understand why you wouldn't do it.

Remember these bad boys are lean from the factory and if you introduce less restriction in the exhaust system, regardless if you change your airbox or not, you are running the risk of being even leaner.

Very worthwhile doing the jetting. I think 99% of the guys here would agree.

 

i agree, i was just sayin as long as you leave the intake alone (stock snorkel and airbox) u dont need a jet kit. it is well worth the $70 to get one though

 

I know it's been 10 days, but...How did the bike pull w/just the TBR slip-on while stock everywhere else? You say "it ran great," but was it much stronger, sharper, rev out faster, etc.? Did your gas mileage go up?

I'm looking for a little sound, looks, weight savings, and power gain from the bike w/minimal cash/time input, while still maximizing fuel efficiency. Your take on those goals w/the stock set-up plus a slip-on? Since you've been there...

Thanks.