Wondering if all u guys and girls can give me some suggestions on aftermarket mods such
as sprocket sizes and carb and pipes u all use and why. Im interested in BB 351 kit as well.
If any one has this mod, please tell me what other kind of work needs to be done to make
this bike all it can be. Looking for all new exhaust and maybe gearing (sprockets). My goal is
to have this bike geared low for trail riding as well as some short enduro track racing. My
street riding will be very limited. Short 4 to 5 mile jonts on the street to the trails. Top end
speed is not a concern. Would like some low end snot for in and out of burms and tight
corners. I have a Kaw 220R that I love. But not being street legal is a bummer. Dont want to toe the bike all the time. Thank U guy's in advance for all your advice. Its great to have a place like this to get info as well as pass it onto others. Keep up the great work !!!
Glen

 

I just bought an 09 KLX 250s.I changed to a 13t front sprocket and got more low end power . I dont know how many teeth are on the year you have but dropping a tooth will help .rokymountainatv has 12-13-and 14 tooth sprockets .Mine was $8.99 plus $7.99 shipping> Good luck.

 

My first mods were a high flow filter and removal of the smog stuff. Stage 2 was a FMF Q4 pipe and a rejet. From the factory, the bike is choked up and needs the intake/exhaust mods to be the way it should have rolled off the floor!

I still want more, so I am thinking about the 351 kit over the winter.

I am checking out gearing, too- I might consider that 13T in the interim, but I wonder how much top end I will lose.

Edit: Saw that timely thread on the 13T. I am going to try it!

 

I have a2007 with a full muzzy exhaust, no air box lid with a twin air filter, geared 14 50s, modded carb slide, cut coils off vaccuum slide spring, and rejetted, competely different bike than stock. At 1 point I had it geared to 13 51s, too slow on top, gearing now is faster than stock but rpm is very high pinned in 6th.

 

There is no replacement for displacement. As far as big bores go you have 3 options.

1 Go buy the cylinder, piston, wrist pin, piston rings, and gasket kit for a 2007 klx300r and replace the same klx250 parts with them. This will give a bolt on upgrade to a 300cc using kawi parts. Will be a signicant difference in power from 250-300. You may find yourself sitting closer to the tank when you hammer on it.

2 Buy a big bore 331 from either bill blue or kustom kraft. This will obviously make your bike a 331cc bike. Probably not going to be a big difference in power from a 300 to a 331. Will be significant going from 250-331 You may find yourself sitting closer to the tank when you hammer on it

3 Buy the 351 kit from bill. IMO this is pushing the envelope of what the motor can handle because it cuts extremely deep into the water jackets. It will make the most power. Will be a significant difference from 250-351. Depending on your weight you may find yourself sitting closer to the tank when you hammer on it.

After you go bigger cylinder pick your favorite sounding exhaust. I like the sound of the big gun, Some like FMF, Some like 2 Brothers. Each manufacturer claims to make more power than the rest of them. If it is true it is only minimal. The biggest difference will be the sound and the loudness.

IMO, leave the air cleaner cover on and get a snorkle from the 2007 kdx220 and replace the snorkle on the klx with the kdx snorkle.

Buy a better air cleaner. K&N breathes the most but also lets in the most ****. I find that uni is a nice in between.

Call John at Motto-Pro and tell him how heavy you are and what type of riding style you are and he will set you up with new front forksprings as well a new rear spring and shock if needed. If your really aggressive you can also revalve the front forks.

Then go ride it like you stole it with a **** eating grin the entire time your on it.

I know the next question coming will eventually be how much.

The parts cost-
300cc upgrade about 480.00- I Did this
331 upgrade(bill blue)- about 400.00
331 upgrade (kustom kraft)- about 700.00
351 upgrade (bill blue) about 500.00+
Air cleaner- 15-50.00- I did this
snorkle- 13.00 from dealer- I did this
front fork springs about 150.00- I did this
rear spring- a couple hundred
rear shock- not sure
new exhaust 200-500.00- I bought the big gun full exhaust- With some of the after market exhaust you have to repack them every so many hours.

I dont have a bike at the moment. However, if I had another 2007 klx250 I would have done the 331 kit.

Have fun!

 

If you are going to get the 351 do that first then worry about exhaust and gearing after you get used to the 351

 

Buffalony, another newbie on a 2007 250s. Looking to give mine a kick in the #$@ also. I am looking for something simple. For someone who is relatively competent mechanically but not having worked on these before, is the 300 kit (bolt on you mentioned) require any mods to the bike for fitting, can it be done with the engine on the bike, and what would you expect as typical hours to do the setup.

Also wondering what corresponding mods to the bike should be made as far as jetting the existing carb (certain kit or jets when going to a 300 bolt on?) and also pipes, looking for something that is still quiet but better. heard the klx 300 header and exhaust fit the 250, was thinking this with the upgrade and the ability to add/remove the plug depending on what/where i am... is this reasonable?

thx

 

If you are relatively competent mechanically you won't have much trouble with the big bore. Couple of clues, don't drop the cam chain I zip tied mine to the camshaft chain tensioner. When you remove the cam buckets don't let the shims fall out. You do not need to remove the engine out of the frame.
The Dynojet kit is a good upgrade to the OEM carb.

 

First let me clarify something that I may have confused you on.

All of the big bore kits will a direct bolt on. The 300 upgrade is just a bolt on where the cylinder did not have to be machines to the point where a sleve was pressed in place of the existing cyclinder and they are all kawi parts which installed at a kawi dealer should be covered for failure by the kawi dealer. Versus if you buy the 331 or the 351 kit the process of adding that many more cc's required the cyliber be bored out to the point where the water jackets have been exposed an a new larger cylinder sleeve was pressed into its place.

Either way the 300,331, and 351 are all direct bolt on hp's. I had mine put on by the dealer because when I was employed and had my bike I did not have time to do it. SO I dropped it off in the AM and picked it up in the evening.

If I did it again this is what I would do!
1 buy me the big gun exhaust(this my opinion on what sound I like)
2 buy the 331cc big bore kit from Bill Blue
3 buy the emissions block off plate from bill blue
4 buy the dynojet klx300 jet kit for the 2007 klx 300r
5 buy the 2007 kdx 220 snorkle
6 DO NOT BUY THE PUMPER CARB- I did and then sold it. To be honest I saw no noticable improvement with spending 400.00 on a carb versus spending 60.00 on the dynojet jet kit.
7 buy a better quality air filter.

Do all of these upgrades at the same time and here is why!
All of the stuff mentioned above will affect the air/fuel ratio and if you do these all at once then you will only have to go through the rejetting proccess once.

Pulling your carb out 15 damn times until you get all the circuits in your carb tuned correctly is a pain in the ***. It also takes some knowledge or what your spark plug should look like as well as how your bike should sound when it is running most efficiently. The idea in carb tuning is to give the motor enough gas to make the most power without giving the bike so much gas that your passing raw fuel out the tail pipe(black smoke)

There are gas analyzers that will help you with this stuff if you really want to pull your hair out and do it over and over again. They are not cheap. Most of them are not specifically created for motorocycles so it may require some welding and cutting of the exhaust so you can get the probe in.

tune your suspension when ever you want. Obviously, if you way add 5+hp to your bike and dont tune the suspension your probably not going to get the most of your ride.

I did not do all the upgrades on my bike at once, hence the learning curve on why I will do them all at the same time on my next bike.

The most important part is you have fun and be safe!