Appreciate all the ideas.

Im no mechanic, so MCM is kind of out .

Its interesting people saying 80-85mph is stock.

FTR its carb, not EFI. Well sprockets are easy to change, maybe ill go that route to start (not sure what will help top end the most, ill have to look at different gearing combos).

I wonder if the canadian version is limited?? What could be causing 10-15mph lower speed? As far as i know the KUBA link is all i know that was changed\added, I bought it with 1200kms on it.

 

Also, Im 190lbs...maybe the guys going 85mph are 150?

 

I am 195 lb. The stock bike may not do 80 easily or even at all. It is a small engine and needs to spin to do anything. You need to rev it up around 8500 rpm on shifts when running up to top speed. It won't respond well to lugging around especially in the 60 mph range and above. You're pushing a lot of wind. The engine can take it having the off road only background from the original KLX250R in 94 up through the KLX300R

At the least it needs jetted. The easiest jetting is the known KLX300 stuff ordered at a Kaw dealership. There is a link to a page in my signature. Includes part numbers. Dyno Jet makes a kit too. Seems there are cases of riders who have issues with the DJ, but in my search for information I didn't find any riders having problems with the Kaw parts. Maybe there is, but I never found it. The only thing I saw was going larger or smaller on main jets depending on elevation.

The KDX snorkel alone is almost twice the size of the stock snorkel intake for the off roader who may need additional blocking of water/mud. If the riding is mainly road use skip the snorkel entirely, pulling the stock one out or remove the lid entirely. It is pretty much guaranteed you will run way too lean if the only thing you do is remove the lid or pull/replace the snorkel. It takes richer jetting to work.

I can tell you the 40 pilot/mix screw starting at 2.5 turns, N1TC needle/clip in second notch from top, and a 125-128 main jet will work with the stock pipe and either the KDX snorkel or snorkel pulled out. You can find back up on this yourself if you search. It has been mentioned in numerous KLX forums and pages. I just set up a link with a document of what we found.

Do NOT compare any Kiehin jetting numbers to Dyno Jet numbers, they do not directly match up from what I've read. Since I didn't buy a Dyno Jet kit I don't know how their numbers compare. Some are doing comparisons, but I'm not spending the money to do so. I go with either Kiehin or Mikuni parts for the respective carbs to avoid confusion for me.

Key thing to remember when riding is the bike has its peak horsepower rated at 8600, not 10,000. 10,000 is just where there is marking on the tach. Consistent for Japanese bikes, the red line is 500-1500 rpm higher than true horsepower peak.

The MCM can be done when valves are checked and reshimmed. Just make sure to disable the compression release or remove it. The bike spins and starts easily without the compression release. Two lines of thought, one is to just remove the spring, I preferred to pin the shoes disengaged to eliminate part movemeny, both work. Best is to press it out, removes rotating mass lightening drive line parts.

Summary - at the least do the jetting and try it out. Let the engine rev and you will find stock or higher gearing will work. Let the engine sing a bit to get best performance. It ain't a tractor. It won't pull if you don't rev it. I can tell you it will pull the 15/39 if you let it rev. The stock KLX250SF runs a 14/39 for its more street oriented supermoto design and Cycle World's review of the 09 model said 75 mph at 7500 rpm.

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My 2011 is a Canadian model and wouldn't go much past 130kph indicated (approx 117kph actual). Better after re-jet (Dyno Jet Kit) but not much on top end. Don't really want to exceed 110kph for long with this lite bike anyway. TheForechecker, where are you in The Great White North? Maybe update your profile with a location. I now have installed a 351 and TM33 pumper carb so I have a Dyno Jet available if you want to go that route depending on where you live.

Never mind, just saw photo of your bike. Oilers sticker kinda gives your location away!

 

I'm surprised that nobody else find it strange that your bike can't exceed 65-68 mph! Maybe see a good dealer and tell him that the bike is lacking quite a bit of hp.
Regarding gearing I agree that a taller gearing will slow you down even more. To see what a shorter gearing does ride the bike in 5th. Bet it will be faster.

 

Dang! Pre-empted even before I could say a single word.

 

Hmm well online, most sites list the top speed at 65MPH. I tested again today, and it "indicates" 78.3MPH (126kmph), but my GPS says 70MPH.

It goes and stays at 8000rpm, just curious would that hurt the bike to drive wide open like that a lot?

youtube - 2012 klx250s top speed (indicated km, GPS MPH)

 

I've done the mcm, jet kit and fmf q4 exhaust... I've been up to 125kph which is plenty fast for such a soft sprung bike. I'm happier at 90-95. This ain't a highway cruiser.

 

I guess the real (rhetorical) question is if you plan to use the bike a lot on highways at speeds around 70 mph why did you buy a 250 dual sport? A good used 400-650 dual sport or street bike will do higher speeds all day long.

First thing consider having the bike checked out to find out why it will only do 70. Seems even stock, that Cycle World was able to pull 81 mph out of the bike.

Second thing jet the bike. Either do the KLX250 Cheap Mods jetting from the link in my signature or buy a Dyno Jet kit. The bike is lean, even with the stopped up exhaust it is lean.

Then buy some sprockets. Some riders claims gearing smaller is the trick, others say gear up. I'm among the ones who has actually done both, but find gearing up works for speed. I geared down for off road. I did a 15/39 on the road and a 13/47 on the dirt. I am going to a 42 to match up with counter shaft sprockets. I will use a 13T for dual sport and stick on a 15T if planning more road work. I think I made a mistake again, I should have gone with a 45T. Thing is I have the 650 for the serious road use.

For what it's worth, I ran the 15/39 easily to 70 mph and would creep up over 75 mph indicated, not pegged, just riding. I also ran the 13/47 at about 65 mph down the highway on a dual sport ride, really twisting it up. I wasn't overly thrilled, but the engine didn't seem to have any issues.

The only way you will find if anything here will work for you is to do it. Buy a 13T counter shaft sprocket and try it - the least expensive first. Then buy a 15T sprocket and try it. If you want to spend the bigger money if mainly riding street, buy a 39T rear sprocket. All three probably cost less than $100 total.

 

As KLX678 covered, the kawasaki jets / KDX snorkel made a big difference. I used the dynojet kit for the 250 using the stage 2 instructions. 128 dynojet main and middle clip on their needle. Aus main is 135 keihin ~ same as dynojet 128 but I had it apart anyway.

The next best way I found to get better top speed was to lean forwards over the fuel tank 110km/hr uphill in 6th.

Stock gearing isn't too far off the mark. Tried 15/42 but wind and hills meant I was in 5th much of the time (very similar ratio to stock 6th) and 1st was too high. 14/44 seems to work well and I can hold 6th nearly everywhere. Roughly 7000 rpm to get 100km/hr on a near new stock D605 rear tyre.