Took six hours last night:
1. N1TC Needle, Clip 2nd from top with Collar
2. 125 Main Jet
3. 40 Pilot
4. Fuel Screw 2.3 turns (stock was 1.5).
5. Crank Vent drilled to 3/8"
6. Stock Exhaust drilled 1/2"

My unscientific dyno: 3 mile uphill steep grade

Before: Maxed out at 70 mph 6th gear, no headwind.
After: Maxed out at 80 mph 6th gear, no headwind.

Bottom end: slight improvement
Mid range: pulls smooth and hard
Top end: 7K rpm to 9K felt significant improvement

Problem: Engine dies when not completely warmed up (e.g. coasting to a stop with the clutch in). Problems goes away after completely warmed up.

Spent total of $60 on mods. This is the best horsepower return per dollar for sure!!

I'm going to get the Big Gun instead of the Muzzy because so many of you posted complaints about quality (e.g. missing spring hook and no room for passenger footpeg).

Anyone: Will the full system Big Gun make a big difference, on top of items 1 thru 6 above?

Anyway, thanks to all for the great tips. This forum is great!!

 

Congrats !

Did you do any MOD to the Snorkel (remove/replace)?

I just changed my snorkel for the KDX and I like it.

I am waiting to do the Carb MODS until the MUZZY is fixed (yes, one of the unlucky ones). I have been scouring the posts for Carb hints. I was going to have the dealer do it, but I think I will give it a shot. Some posts say a couple hours and some say more.

Any hints to pass on if you were to do it again?

 

big gun is definately worth it. carb mods pretty easy if your mechanically inclined. got damn water in my snorkel again, had to use the drain to get it out of the air box .... anyway, i have done all of those carb mods, except i have my needle on the third position from the top, and the air fuel screw at 2 turns out, was runnin a little rich, ok i was wondering guys, is it better to screw the air fuel screw in or change the clip position on the needle, i know which one is easier, and one thing i have noticed with the muzzy, might be wrong, the head pipe is not chrome and gets "dark" my head pipe with the big gun has a chrome finish and all the baked on mud just wipes off with a little water. and its looking good and i think it will stay that way. just another piece of info on considering the two.

 

tasod
I took off the snorkel. Forgot to mention that...only cover. I like the throaty sound. Tips if I were to do it again:
1) Take off the the emission stuff. Someone said you need the emission stuff with the stock exhaust to generate enough heat for the catalytic converter (lack of heat may clog it???). Since you are getting the Muzzy, I guess the emission stuff may not be necessary. Anyway, my point is the emission stuff is a lot of clutter underneath the tank, and makes it hard to remember how to route all the cables n stuff.
2) I printed photos of the various mods. That was helpful.
3) Getting to the airbox to drill the 3/8" crank vent was a pain. I couldn't figure out how to take off the metal screen inside the box without taking the box apart. Instead I took off all the bolts attaching the airbox to the frame and the rear mud flap. It gave just enough room to get that 3/8" bit into the box from the outside. Take off the hydraulic reservoir for added room. Used a shop vac to take out the bits of plastic.
4) Remember how you take off the throttle cables and how the cables are routed beneath the tank.
5) The fuel screw cap was thicker than I thought. Careful not to push too hard when drilling into the cap or you might nick the fuel screw. Need to have the right size slotted screwdriver to fit into the opening. Seat it first, clockwise, counting how many revolutions (mine took 1.3 turn to full seat). I then back out the screws 2.3 revolutions.
KLXStiffler gave good pictures of how the N1TC needle fits into the assembly, and how the collar fit on top of the clip (between the clip and the white needle holder.
6) I didn't need to soak the black rubber slide diaphram in how water like an earlier posting recommended. It fit right in, no problem during re assembly.
7) If you work takes as long as mine did, start early in the day or be sure to have your work area WELL LIGHTED!! Hard to see in the cramped areas with out additional light at night. I used one of those L.E.D. lights that strap to your forehead. Worked wonders.
8) If you can get the step-by-step pictures downloaded (they are there all on this forum) you'll probably do fine. Again, pay attention how your cabling and tubing is routed beneath the tank so you can put them back the right way.
9) Don't remove the flange attaching to the carb intake to the head. You don't need to. Just completely remove the duct from the airbox to the carb and pull out the carb from the fitting on the head side.

Hope this is helpful. Probably more info than you needed. Noticed you are from Mililani. I am too. I ride behnd the prison and graveyard. Some weekends a bunch of us go camping up at the Kahuku racetrack, if HMA allows it...usuall on the three day weekends.

Good luck. Let me know how your Muzzy fits. I'll let you know how my Big Gun EVO works out.

 

Thanks for the great tips Bulls - amazing you are in Mililani also.

I live in valley below oceanic (all the way in back). Between posts just did a quick ride up to Kaena point to play a bit. My "garage" is a dang carport here so have to plan the mods carefully!

Hope to see ya on the rode sometime and if you ever need an extra pair of hands just give a yell!

 

I understand a "quality" issue with the spring hook ordeal. But, the footpeg problem is NOT a quality issue. The Muzzy exhaust is designed for the KLX300R not a 250S. There are no rear pegs on the target bike, likewise, no fitment problems.
I tend to lean toward the Muzzy as the head pipe is made of stainless not corrosion prone carbon steel (Big Gun). There is a lot of moisture where I live and the stainless is a must. I imagine that most of you live in dry climates as I have never read any mention of this difference in everyones Big Gun vrs. Muzzy arguments errr discussions, yeah that's what they are called.
I called Muzzy today and they said that this KLX system is fast becoming if not already has become the hottest selling system in Muzzy history. They have been doubling production runs only to find that they are still behind the order curve at the end of each. They must be doing something right!

C6

 

I wonder if they realize that all these new KLX300 pipes they are selling are going onto KLX250S's? If they knew this, maybe they would tweak their bend to avoid the footpeg.

I love my Muzzy. But then again, mine has two hooks. I don't blame folks for being upset about the missing hook. It's not like these things are real cheap. For the prices we pay, I expect to not to have such glaring flaws.

 

Muzzy can thank this forum and advrider.com (100 page thread on KLX250S in the thumper forum).
Oodles of free marketing for them!

 

Hmm, I didn't vaccuum up any chips when I drilled the airbox. I used the vise grip approach and I was pretty sure it came out in two chunks as I had 2 spaghetti like pieces of plastic up through the bit's flutes. I've ridden a good 75 miles since doing the carb mods etc and ahve thoroughly enjoyed the improvement!

 

I think i am the only one who actually took off the air box, and took off the mesh screen and reinstalled everything, Mental note for everyone: NEVER EVER TAKE THE AIR BOX OFF.... EVER. the biggest pain in the ***..