I had real good luck with K&N on my KLR. I'm going to go with something better at some point but the bike is screaming along just fine with the stocker.

Gas mileage will be very interesting to me too given the tiny tank. I'll post an update soon.

Tony's right about the needle being fatter. Even on clip position 2 (out of 5) it sits about 1/8" higher to begin with. I need to do a plug check to be sure but it doesn't seem to be running rich at all. No bog or smoke on hard accel.

 

Ok guys, I drill out my exaust today and the bike surged quite a bit in the freeway. So I went from the 120 jet to the 125, and pop went the front end, zoom went the tach, and RRrrrRRRrrr went the rev limiter. I was a bit surprised. With the bike warmed up, it was a smooth all around power increase. Now I'm going to start a cold weather thread.

 

Okay, okay . . . . . whoa here Nellie Belle!

Sounds like we got so many things going on . . . . . . my head is starting to spin.

Last comment - drilled out the exhaust, now it surges - changed to 125 jet, now it rips! I would like just a bit more detail!

Actually I don't mind putting this all together, complete with pictures. If it helps anyone here at this site, so be it.


Thus far I see Todd doing a lot of low-cost motor tweaks.

Tony has only gone with a 13 / 45 and now some jet change after knocking a hole in the muffler. Is it still spark arrested?

Lots of things in this one thread, almost enough to make even me confused!

 

OK, I'll try to summarize to make a bit more sense of what I've done. My goals where twofold:

1) Increase RPMs to better fit the power band - This was accomplished primarily by changing the gearing, thus the 13t counter shaft sprocket.

2) Increase HP - As Marty pointed out, you do this by increasing the amount of air and fuel moving through the engine. Our little KLXs are strangled by the factory to meet EPA requirements. The key areas we examine today are:

Air box (snorkle and air cleaner) - More air in

Carb needle jet size and position - 1/4 - 3/4 throttle
Carb slide spring and vent hole - Throttle response
Carb main jet - 1/4 - full throttle
Carb pilot jet - 0 - 1/4 throttle
There are other factors but these are the key areas to consider first

Exhaust - More air out

So, let's begin:

AIRBOX - Per Tony's suggestion on this forum, I removed the OEM snorkle from the airbox lid and replaced it with a Kawasaki KDX200 snorkle part number 14073-1577. This allows mucho more air into the airbox. A less restrictive filter would be a good thing too but just changing the snorkle is a big win.

CARB - The KLX250S comes with a fixed needle jet. I elected to replace it with an adjustable needle jet from a pre-'06 KLX300R. This allows fine tuning of the midrange. I forgot to take a picture of it but you can find one easily on the web. Replacement is straight forward. Just pull the top off the carb and CAREFULLY slide the diaphram and carb slide up and out. Don't let the spring fly away! I put the needle adjustment clip in position 2 down from the top (5 total on this needle) based on reading others experiences. This proved to be spot on for me. Be very careful not to pinch the diaphram when replacing it. Even a tiny hole ruins it.

CARB - I increased the main jet from the stock #118 to a #122, again based on reading and guessing based on how much I intended to open the airbox and exhaust.

Here's the carb taken apart on my bench. Note that all this work could be done with the carb on the bike but it's SOOOO much easier to work on if you remove it.



Looks like a lot of work to get the carb out but it really isn't



CARB - When replacing the needle jet, it's also a good idea to drill out the slide vent hole to increase the rate in which the slide moves up and down in reaction to changes in engine speed. This improves throttle response. Be careful however, too big is not good either. 7/64ths seems to be just right.

CARB - I also drilled out the little plug over the pilot air mixture screw. The EPA doesn't want you to change that screw's position but it needs to be backed out. Mine was set at 1.5 turns out from the factory. It's at 2.5 turns out now. This reduces lean popping (popping on sudden decel).

EXHAUST - I drilled out the OEM exhaust using a 1/2" bit to place a hole in the first plate you see when you look in the exhaust hole.

MISC - In addition to the above, there are two additional mods being discussed, one helps HP, the other is cosmetic.

I removed the so called Smog stuff (Called an Air Valve by Kawasaki or an Air Injection System by others). THIS IS PURELY COSMETIC for all intents and purposes. It cleans up the under-tank area and reduces the chance of a vacuum leak down the road. It also reduces the temprature of the exhaust which reduces pipe bluing (not an issue on a dirt bike).

Here's a picture of the Air Valve and plumbing:



Here's the plug I made to cap the Air Valve opening at the front of the engine head. This covers the reed valve into which air is drawn by vacuum. I elected to include a small section of hose to keep the plastic plug from getting too hot:



Here's where you plug the airbox once the plumbing is removed and a pointer to the crank case mod. The latter helps the engine by reducing pressue in the crankcase. NOTE, you also need to plug the vacuum port on the front of the carb (the place the small hose was attached too.

 

Sorry Marty, when I drilled the the exhaust with a 1/2" bit as Don did in post 34, it created a 'lean' condition. I wanted a 122 jet, but it was Sunday and I had a 125. The spark arrester baffle is deeper in the muffler, no worries there.

Tony's update:

hi-flow snorkel with a well oiled filter to stop carb icing
125main jet
drilled slide valve with #30
drilled first exhaust deflector plate with 1/2 bit
13/45 sprockets with 109L chain
Bridgestone TW302 rear tire
acerbis rally pro brush guard w/spoilers
1585 on the odometer
1ea warm fuzzy feeling when little kids are stuck to the car windows yelling 'look mom'.
ordering the 1.6gal acerbis tail mount fuel tank 1/24/06

Don't tell Mrs. a16tony 'bout the tank...yet [sm=chairshot.gif]

 

Nice post Todd

 

Excellent post Todd, I'm sure there will be lots of people looking up this post. I wish Kawasaki Australia put a parts catalog on their website so I can see what differences there is in your carbies and mine without opening it up. Oh well.

 

Todd,

Now, that's the typical BMWHD style post you've gotten me accustomed to!

Thanks!

 

Hey Todd, how do you get pictures right in the post, and also how do you get away with them so large, come on give it up. We all want to know.

 

For pictures, I just host them on my website and then embed the URL between [img] and [/img] tags in the post like this:



That's my old BMW K1200LT. Just a bit different ride than the KLX [8D]

You can do the same from many photo hosting sites if you find out how to get a direct URL to your photo.