Klx 250 Big Blue 351 Big Bore Kit

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I just got back from a 8,000+ KM trip thru SE Asia on my extremely used Bill Blue 351cc KLX250 bringing the 351cc big bore kit to a total of nearly 115,000 completely trouble free KM so I wanted to brag on it a bit!!
For those that don't know the KLX250 is a very reliable bike, requiring very little maintenance though some (including myself) would call it boring. (My other bike is a KTM690 Enduro).

At the same time, I think it is one of the most improvable bikes on the market today. The stock (pre 2009) KLX250 weighs 286lbs* with 1.9 gallons of fuel, has a nice wide "3.32:1"* 6 speed transmission and puts out a boring 19HP & 13 ft/lbs of torque at the rear wheel.

Dyno of stock KLX250. (Taken from ZRexRich):

With Bill Blue's 351cc big bore kit, 33 to 34mm pumper carb, and full system exhaust it jumps to about 30HP and 21 ft/lbs of torque at the rear wheel.

After nearly 100,000KM on the completely stock engine I did the big bore kit, pipe, smog block off/airbox mods and pumper carb all at the same time. Obviously it was a HUGE difference to ride, BUT the question in my mind was how reliable would it be? The big bore puts it in a whole different category than the stock KLX250, but at the same time it's still heavier and weaker than a stock KTM EXC 350. To be a success in my mind it still had to blow the KTM away reliability wise.

Pics of stock vs 351 piston/cylinder. (Taken from Mel Brooks)

I know many people that chose to buy a KLX250 over a KTM350 do so because they can't afford the KTM or perhaps they think it's too much bike for them. That is not my particular case though. I chose the KLX because I ride as many as 40,000 miles a year, don't have time to fiddle with it, and can't afford it breaking down on me in say the middle of a war zone in Kachin province, Burma. It was important to me that Bill Blues mods didn't undo the most desirable trait of the KLX250 – its reliability.

I'm happy to say it didn't! If it died on me tomorrow it has still lasted longer than many stock KLX250's I've followed. My KTM 690 by comparison went thru 3 engines and 9 fuel pumps in just 30,000 miles; that would be 6 ½ engines and 21 fuel pumps in the life of the Bill Blue 351cc engine!

In approximately 115,000 KM/70K miles I've checked the valves twice and I change the oil/filter every 3-6,000 miles. I put in a new clutch when I did the big bore and it's gone thru 1 more as well. I also had to fix the starter motor a few months back; the 351cc is also higher compression ratio than stock so that could wear it out faster. (However that was at nearly 200,000KM into the bike total - about 1/2 of that on the 351. My personal opinion is the stock KLX wore the starter out more though as along with the big bore I did the pumper carb. Now it starts most everytime with 1 press of the button; with the 250 and stock carb it was hard to start and required about 15 seconds of cranking.)

Some local shots

No, this is not a crash but it was a huge blunder! I left my bike in the middle of the main "jungle hiway" to do some recon on some smaller trails on foot. Came back and it had fallen over - no biggie BUT most of my gas has leaked out!
what a great review and pictures.... i bet you have some amazing ride pics/videos. if you have a blog please post.
Very cool and thanks for the info and the review. That's some excellent reliability you got there. BTW what kind of gas mileage are you getting with that big bore kit?
TNC Candyass Camper

Joined:

Mar 22, 2007

Oddometer:

5,563

Location:

Tejas

Way to go, Ricky. We've talked on posts for some time now, and it's been interesting keeping up with your KLX history...and even your KTM fuel pump issues.
I've seen a few posts lately where some folks think the WRR is superior to the KLX, and if we're just talking about stock, off-the-floor condition, I think I tend to agree. However, I think the KLX has shown more suspension potential...especially '06/'07 models...and more engine potential. Couple that with the extremely wide powerband of a modded KLX, and I think the KLX gets somewhat overlooked just because it's been around awhile and uses a carb. It's good to see the kind of durability results you've experienced here. I know you ride the wheels off your bike, but you also take care of it. Keep 'er going.
Nice review for sure, thanks for your insight, and the great pics
In my mind, because the KLX 351 has proven itself reliability wise its interesting to compare it to some of the stock dual sport bikes in the same category of low maintenance/ high reliability.
I'm taking the following info from Oct 2009 Motorcyclist and Aug 2010 Motorcycle USA who both seem to indicate that they actually weighed these bikes and put them on their own dyno to measure rear wheel hp. I know this is not super accurate... just kind of a ball park figure!

--Bike---------------RWHP-------------Torque---------------Wet Weight

07KLX250...............18...................12.4ft/lbs..................285lbs
09KLX250...............18...................12.4ft/lbs..................299lbs
10WR250R..............24.............. 14.9ft/lbs.................299lbs
MyKLX351...............29.5................21.3ft/lbs.................285lbs
DRZ400SM..............32.5................23.7ft/lbs.................335lbs
MyKLX300 w/351 29.5................21ft/lbs...................260lbs*
******Here's the ADJUSTED* Cycleword GYTR WR290R
WR290R................ 28.3............... 19ft/lbs...................299lbs

FWIW I have a 2008 KLX250 which many countries did not get. It's the same as the USA 2007 spec but with the KLX450 digital meter. In 2009 the KLX250 shifted to be a bit more on road biased - it gained about 16 lbs to 299 wet weight, lost an inch or so in suspension, different wheels, swing arm, brakes, dash etc.
I also have a KLX300 converted to 351 in the US that was a phenomenal deal! It has KX250 suspension.

Random thoughts on the bikes in this chart:

My bike compared to a DRZ400 is interesting and for me, I certainly prefer my KLX351. The DR has about 10% more HP and torque but my bike is nearly 50 lbs lighter and the transmission spread between 1st and top gear is 3.32 vs 2.65. (That means that doing 10 mph in 1st gear, at the exact same rpm in top gear the KLX is doing 33.2 mph and the DR 26.5 mph in top gear.)

Compared to the WRR - the WRR has quite a bit more electrical power and it also beats mine significantly on fuel mileage. That's one thing I have NOT gotten sorted on my bike is the jetting. There are guys on this forum with the 351 getting 60mpg but I'm happy to get 40 with mine.
IF the WR290R turned out to be as reliable as the KLX351 I might be tempted to get it IF I lived in America. Kawasaki has a massive advantage in SE Asia - Indonesia, Thailand, Malaysia as there shops are everywhere and they don't sell the WRR here.

*The light weight of my KLX300/351 - it should be noted that
1.) It does NOT have electric start
2.) That is without the Baja Designs dual sport kit.

**Cycleworld May 2011 Did a test of the stock WR250R vs one with a bunch of GYTR parts and the 290cc kit. Their dyno number on the stock one as well as the KLX250 read about 17% higher than both motorcyclist and motorcycle USA - stock 28hp/17ftlbs; 290GYTR 33hp/22ftlbs. I reduced it 17% in my chart to TRY and be closer. Bottom line for their test, they got a 18% HP gain and 30% torque gain.
My gas mileage is not good. On my way north from Malaysia this past month I was mostly taking my time, not too much hard core dirt nor fast freeway miles that really eats it, and I got about 42 mpg using the GPS to calculate my miles. (I'd probably be 10% higher going off the odometer.)
In Burma, Northern Thailand I flogged it in the dirt but didn't keep track of the mileage. I had to fly on the way home so did a lot of 75+ mph average on nearly the Thai #4 and Malaysia's toll road. Got about 36 mpg.

However there is an inmate here Ranger Ron with the 351 whose something of a jetting guru I think whose getting 60+ at freeway speeds. I'm sure TNC who posted above me is killing my mpg as well.
I know my jetting is significantly off. If I was back in the US I would just take it to the most competent tuner I could find and be done with it.
However I have no experience with jetting, of course could learn but am usually insanely busy! On top of that I don't think I can even get Mikuni jets here in the country and are mail is extremely slow and unreliable.
I'd bring it to a local mechanic, but the problem here is that while Malaysian mechanics are genius at getting something broken to run (they retrofitted a KLR650 wiring harness in my KTM LC4) I don't know any who know/understand/appreciate the art of fine tuning . (I dropped my bike off at a shop once because the rear brake was out, went to pick it up and it was the same. I complained forcefully and the shop manager put his arm and my shoulder and explained to me that I actually had 2 brakes and that they ran on separate master cylinders and I didn't really need to be worrying that my rear brake was out because I had another one!)
Thanks TNC - I've always appreciated your posts and your helpful KLX insights!
I absolutely agree with your point above and for that reason hope this thread is helpful - realistically it wouldn't be fair to expect the magazines out there to do comparisons shootouts with "slightly modded" or even heavily modded bikes. Sometimes they do and I appreciate when they tell you; such as I just read a test on the Husky TE250 where they complained of horrendous performance BUT after snipping a couple wires, removing a screw and doing a reset it ran twice as good.
I've thought it would be interesting someday here to do a thread on "Nominations for the best 'modified' reliable dual sport bike." That might help many of us realize a bike we had scratched off our list was actually pretty close to what we were looking for.
i know this is apples to oranges, but city riding with heavy throttle with a cv carb (main jet at 132), I get about 56, driving with a good throttle hand I get 60.
Thanks for your update! Here is hoping my 2009 KLX250 EFI will run just as long. The best thing about this bike is the super helpful community! If it wasnt for people like you. I would still be riding the stock, somewhat weak bike.
My mods include:
292cc OEM Kawa big bore cylinder and piston.
FMF Q4 Slipon
EJK fuel controller

I've got around 8000km on my bike so far. Ive got a few problems. Its getting rather poor milage(21km/l) and I have to press the starter button a few times for it to start up. I am rather new to bikes so I have no idea what the causes could be.

Also debating whether I should bother with an FMF slipon, but atm I am thinking its not worth the extra money.
Hey Nik, not sure if you do or don't have the FMF slipon. The pipe does make a pretty big difference on this bike. Here's a dyno of the bike with the 351 but no pipe/carb.

At the same time, I really do like/appreciate quiet so you have to consider that as well. If you post up in the long term KLX250 review perhaps Ranger Ron could give you some pipe ideas as well. He's got a great running maching, getting great gas mileage and I think claims its not too loud!
This is a great review. Good to see there are folks out there riding this much. Wish it could be me!
Keep up the miles.

-A humble KLX250s w/ 351 big bore owner
ohenry Been here awhile Supporter

Joined:

Oct 13, 2007

Oddometer:

510

Location:

GA

Great job on this. I am just waiting on my tax return and 351 will be on the way! Thanks for this info it really helps!
Ohenry
I did counter that even with a total population below 30 million they do have an average of 5 1/2 reported motorcycle fatalities and 78 major injuries daily!
He said, "Oh! That's because sometimes the OTHER master cylinder goes out and then they don't fix it!"
Hey Ricky.
I wrote wrong in my post. I DO have the FMF Slipon, what I DONT have is the FMF header. I dont know if its really worth it for me. Seems rather expensive especially with shipping from USA + European import taxes.

Good to hear that the pipe makes a big difference though. I've got it mounted during the winter here but still havent taken it out for a spin with the pipe, got something to look forward to
Nice thread Ricky.
That is another cool point on the KLX engine TNC. I've done over 220,000 dual sport miles in the last 7 or 8 years or so riding many different bikes and would say the KLX250 and 351 have one of the most friendly powerbands if that's the right word? I guess what I'm trying to say is that it is one of the most predictable engines - about the opposite of a 125cc 2 stroke MX. A 500cc 2 stroke is much scarrier, but the 125 2 stroke is the opposite of what I'm trying to describe about the 351. The 125 has no power except for in a very narrow band.
I haven't ridden the CRF250L but from the dyno charts it looks very similar and maybe even more "gradual" than the KLX.
Another super "gradual" engine is the KTM690 with the fuel mapping on "soft power" - that's actually probably one of the most beginner friendly engines out there!
So often I found on my 690 when I couldn't climb an extremely steep, slippery, gnarly, rocky, rooty hill if I switched it to soft power it was a piece of cake. At first it was counterintuitive as I thought for a hill that steep I needed all 63 HP! But that is what the KLX351 is great at... it makes you look good climbing steep hills in low traction situations!
Honestly, I think the KLX is completely under appreciated motorcycle. However, it is let down by crap suspension. I know it can be made better, but Kawasaki did let it down by cheaping out. I love the bike and wouldn't mind owner another one, but that will be high on the list of changes to be made. (Like a BB 351 kit. )
Your absolutely right Kawidad. My KLX in California has been converted to KX250 suspension so it's great in that department! I didn't do it myself but bought it that way. Fortunately the original owner weighed about the same and got it all dialed in for me.
I am thinking about getting a new bike at this point. Though the 351 has been amazing, the whole bike with about 125,000 miles on it is starting to have "nagging" issues all over.
It's a funny contrast to my KTM690; My 690 never once ran poorly. It either ran awesome or it didn't run at all. Unfortunately it spent a lot time "not running at all." At one point KTM NA was completely stumped and had to ship the engine to Austria.
My KLX on the other hand has never left me stranded; but more and more now is having issues with bearings, frayed wires, blown seals, ignition you can start with a knife etc.

I ride a lot (about 30,000 miles a year), know what I want and have finally come to accept no one makes that bike! My latest thought is this:

I want to buy the higher performance, lighter, yet higher maintenance KLX450. (It comes street legal with lights etc here and is about 24 lbs less than the old 250; 40lbs less than the 2009 and newer 250's).

Right away I'll probably add a custom, stronger sub frame as I need to carry lots of weight around with me, a cush drive rear hub and either a Highway dirtbikes or Brittania composite dash enabling me to have improved lighting (a huge pet peave of mine - lots of driving in 3rd world countries at night - pot holes, no reflective paint, oncoming traffic with no headlights using the same side of the road, and many times I've come across elephants, water buffalo, pythons and wild boar crossing the roads.)

The plan is to enjoy the power and light weight until my next long trip to the middle of no where. Then what I'd really like to do is figure out a way to put that uber reliable 351cc motor in the KLX450 frame.

I've never anything like that before and frankly don't know if it's possible or reasonable. Anyone reading this that has any thoughts or ideas on that let me know!