KLX 250 rebore

LED Kev

LED Kev

Member
Joined
Jul 24, 2011
Bikes
Kawa Er6n & KLX 250
I was surfing the net and saw a couple of articles on reboring a KLX 250 to 331 for around 30k
Has anyone tried this in Chaing Mai or know anyone that has this done
 
Theres a 331 and 352 big bore kit.. for the Carbed model KLX.. The Bill Blue ones.

Many people have tried to make them work with the EFI models.. And theres one or two people (from all those who tried) who claim to have it working properly.. But reports of the others lead to badly running, poor fueling bikes. That never ran right.

Theres also a very expensive japanese kit, with a efi feulling module thats interesting, but its japense mega pricing and all info in in Japanse Kanji.. I have never heard a report of this being installed in western text.

If there was a simple 'buy these bits and bolt them on' conversion for the KLX250EFI to a functional 330 of 350 it would become majorly appealing, but for all the writing online, it doesnt seem like that is there.

I would love to be proved wrong.
 
the 331 kit takes a 83mm piston, which is impossible to find locally, and expensive to order from states.
You could buy a KLX 300 barrel and piston for under 10k,or geta 300 sleeve put in your 250 barrel locally for under 5k inc kawasaki 300cc piston.
350cc requires a different stroke on the crank.
If you have carburettor, ok, you would probably want a bigger carb to get the most of the extra displacement.
If fuel injection, there are things like a Power commander which you would need to alter the mapping.These start at around 12000bt I think.
Also it depends what you use the bike for. If you want top speed, modifying the mapping maybe best.
If you want more power at lower revs, there are other mods you can
do
 
Hi guys thanks for the quick & knowledgeable reply.
I am looking at buying a new KLX to do a bit of off roading around Chaing Mai. I only want to get a new bike with a book, but was happy to pay a bit extra to increased performance. What you say about the carb and EFI models makes sense. It looks like I will have to get a KLX 250 and add a few mods and then wait to see if Kawa brings out a 450 into the Thai market in future.
 
alexuk said:
350cc requires a different stroke on the crank.
Click to expand...

Really ?? I thought the Bill Blue kit was an upper head bolt on not a stroker kit.

This one http://bandbcyclerestorations.com/page_4.html

Really it just comes back to the EFI fuelling and mapping.. If one of juicebox or power commander guys get it smooth with out of the box components it would be great.
 
Maybe I'm wrong about the 350cc
Anyway, I'm sure you can get an programmable ECU that works well on the 330/350.
But I dont know anything about relative torque or horsepower requirements for racing on road or offroad. So would you want to be able to rev it over 12000 for enduro? Do you want the max horsepower at 7000 or 10000? the ECU tuning may be better for track racing bikes.
 
Here is my personal opinion:

If you want to do "normal" off-road you don't need a big bore kit on the klx. If you do all the mods (exhaust, derestriction, bigger air intake, smaller gearing...) the bike will get you anywhere you want the same way other dirtbikes do.

Now if you want a racing bike, it's really pointless to pick the klx in the first place, because it's main issue is not the power, it's just bike is not design for extreme enduro. My biggest issue with the bike is when I start to go fast on big rocks or so the bike feels very clumsy (because of the suspensions, weight,...). The only issue with the power is it's hard to get the front wheel up (except in first gear), and a lot of shifting with short gears.

If you want to do proper super motard then again pick another bike a 250 is just not enough on the road.

I think people don't get that you don't need 50 hp to go off road... most of the trails you don't even have enough traction to use that power, the most you will go on dirt tracks is 100km/h and that really fast already.
 
MastaMax said:
I think people don't get that you don't need 50 hp to go off road... most of the trails you don't even have enough traction to use that power, the most you will go on dirt tracks is 100km/h and that really fast already.
Click to expand...

Especially around here. No desert racing or anything in Chiang Mai.

If you're a good enough rider to be outriding the power of a derestricted KLX250, then you're going to be just as unhappy with the chassis and suspension.

Might as well go for a real off-road bike if you want to go that fast. If not, an uncorked KLX is more than enough to take you anywhere offroad without running out of usable trail-riding power.
 
alexuk said:
Anyway, I'm sure you can get an programmable ECU that works well on the 330/350.
Click to expand...

Well no ones really clearly demonstrated it 'sorted' and it was always the fueling that was the problem.. The most resounding 'its working' claim was a guy in Indo with a power commander and custom maps IIRC.
 
Heres a graph from a tuning box.
Apparently it will work on a 350cc
6150516022_2de7b8fc1b_z.jpg
 
Looks like the green graph is a restricted klx (dies after 7.5k rpm). The red one is like any unrestricted klx (still with stock pipe and airfilter).

But how does this prove it would work with a 350? I don't get the point of this graph tbh... :hmm
 
The green tracks carry on up to 10000 revs, so are an unrestricted dtracker
There is a hp and torque curve there in green, but the torque is hard to see.
The test was stopped at 10500rpm because thats where the standard ECU rev limiter is.
The new ecu can rev to 14000 (I think)
I cant prove it will work with the 350, but that is what the technician was saying.
 
I read somewhere that changing the cam or cams made a big difference and infact I think someone said it made the biggest single difference of all the performance mods?
I sometimes think about all the possible mods and how easy it might be to get confused as to the benefits of each one and how well they all work togetether. It would be nice to go down a proven road or a choice of proven roads to get to the characteristics you want.I also thought it would be nice if there was a local place with a dyno machine and a means of remapping engine and fuel injection settings to suit whatever changes had been made.
Then I wondered if you did get one to go well, maybe you could look into setting up the suspension to suit or perhaps a front end from a recent motocrosser and maybe most of the back end as well.
 
and here's a torque curve graph from a 250 vs 300cc EFI with Power Commander
You get an extra 15% torque with the big bore
kawa3.jpg
 
alexuk said:
The green tracks carry on up to 10000 revs, so are an unrestricted dtracker
There is a hp and torque curve there in green, but the torque is hard to see.
The test was stopped at 10500rpm because thats where the standard ECU rev limiter is.
The new ecu can rev to 14000 (I think)
I cant prove it will work with the 350, but that is what the technician was saying.
Click to expand...

I'm not an expert but on the green track you can clearly see the power dropping at 7.5k revs, which is exactly what the restriction does, where unrestricted you get top power around 8.5k revs (exactly like on the graph actually).

Putting a new ecu does exactly the same thing as derestricting it by cutting the wire, that seems to be proven based on loads of riders on many different forums.
 
Max, these figures I got from Kawasaki site.
Maximum power 16 kW {22 PS} / 7,500 rpm
Maximum torque 20.5 N·m {2.1 kgf·m} / 7,000 rpm
I thought restricted meant there's a rev limit of 7500 in the upper gears, whereas derestricted will rev to 10k
There are a lot more electronic restrictions in the ECU. Its really been built as a low emissions bike
 
alexuk said:
Max, these figures I got from Kawasaki site.
Maximum power 16 kW {22 PS} / 7,500 rpm
Maximum torque 20.5 N·m {2.1 kgf·m} / 7,000 rpm
I thought restricted meant there's a rev limit of 7500 in the upper gears, whereas derestricted will rev to 10k
There are a lot more electronic restrictions in the ECU. Its really been built as a low emissions bike
Click to expand...

Well it's not restricted at 7500, it just stops pulling, a bit like what you see on the graph. That's the difference I felt before/after derestricting. Before I felt the power dropping at 7500 (but still going up to about 9000) and after I felt the acceleration power staying on up to about 9000. That's just my own feeling of the bike but you might be right of course. How did yours go before derestriction?
 
Which box was it ??

Last time I dug around this topic the juice box people were saying they were testing to try to get a mapping working. That was a good while back now.
 
That API Box does hold promise.. Even posts on some forums it works but no data on thats only 'it should' as far as I can see.

Does anyone have API contact information ?? Its worth chasing down.
 
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