Larger capacity KLX250 B1 ........ ?

[grouty]

I guess many of you KLX owners have found the lack of power a pain.
I bought mine back in 82 and still have it.
Time to ask questions. How far can you over bore the stock liner safely ? What piston to use for a 280 / 290 conversion ? I guess the big bore KZ1000 ones fit the stock rod.
I have a brand new barrel to play with, along with another head.
The standard carb is well past it's sell by date, so will a normal Mik 32 or 34 fit.
Knowing what bits to find is the problem, machining or modifying is the easy part.
I would love one of the conversions done back in 79/80 by I think Wiseco or Megacycle.
Stroking the crank would be an option, but very time consuming.
Any help would be appreciated.

[LWC82PE]

im pretty sure there is an artile in VMX on a readers KLX 250 and he fitted a piston out of a Z900 kwaka to give around 270/275cc he said that was about as big as you can go before case machining and re-sleeving

[LWC82PE]

dont know if White brothers are still going but they still listed pistons in 2004

also try Powroll (usa)

and bert kingston performance in queesnsland. i looked at their website a while back and they listed aftermarket cams for the KLX 250

[GMC]

Their were a couple of kits available in the day.  As LWC says, 275 was as big as you could go without touching the cases. Can't remember if this was achievable with the standard sleeve?
I went for the 290 kit & had the cases machined to allow it.
Their was a stroker crank option too that took the 290 to either 305 or 320.
Ken Colvin did mine in the day, can't remeber what brand the piston was but I think it may have been Powroll, or maybe Wiseco, what ever it was the piston was crap.
I also had a lot  of drama's with this kit as it took the bore very close to the oil passage to the head. It would always end up leaking through the head gasket & frying it's oil. Keep an eye on this if you go this way.
Sorry don't know what parts to use now but if you find out post it up here.
You've done well to keep yours all this time, I lost interest in mine after the gearbox exploded taking out the cases with it.

[JC]

There is a fair bit on developing the KLX in an earlier thread under Kaw. Its a good thread; worth looking up.
Some good articles on it - & nice pics.

2mm larger is all you can go on the std liner. Anymore & they crack as the liner is very thin. Megacycle still list several diff cams for them. They also have a trick to improve oil flow.

Stroking them limits the rpm that can spin to. Its hardly worth the effort apparently.

They have an unusual head gasket - like a thin washer which is not wide enough if you bore it too much, causing the sort of problem GMC states above.

Someone on the forum told me tri-angling the valve seats improves performance on them too.

[cyclegod]

Experience has shown me that the best performance mod done to any 2 valve KLX is to bin the motor and fit a 280 big-bore kitted XR/XL 250 of the same vintage (I've seen a 500 in one too  ) as they are more common and there are plenty more options for getting parts both standard and performance.

http://ozvmx.com/community/index.php?topic=102.0

[grouty]

Thanks for the replies folks.
I have the complete collection of VMX, and as yet have not been able to find the reader resto on a KLX. The article in one of them is good for the history, but does not give me any pointers.
I have been in contact with Powrol (very helpful too). But they do not have any parts left.
Tried looking for the White Bros site but came up a blank each time.
From memory the early KZ1000 pistons will fit for just an over bore. Maybe I will try this route first.
Has anyone tried fitting a standard VM32 Mikuni carby to one of these ?
I am guessing that the settings will be exactly the same as it was for the VM32SS which is no longer available. I want to try this first as I know the original to be dodgy. Reverting to a single cable throttle should not be to much trouble.
I did look at chucking another motor in it, but it would be nice to squeeze a bit more from the standard lump.
Just finished fitting the new side panels from DC Plastics this weekend. Sooooo much better now.

[JC]

Grouty,

Good idea to stick w the Kaw motor. The XLs/XR is considerably longer/larger than the KLX & is a lot of cutting & shutting to make it fit.

It would be worth PMing Derail on the thread cyclegod listed above. He's done a lot of work on KLXs, including boring & stroking. I've seen him race & he & the bike were very quick in the company of some very good/fast riders & bikes even tho his bike is only about 270cc & up against big bore 2 strokes.

When I spoke to him, he said "just bore it 2mm & run a megacycle cam & race 250 class"

[grouty]

Thanks JC.
Derail..... see PM.
So, it looks like a 2mm overbore, Wiseco piston, Megacycle cam, and a few other small mods.
We're getting there. This time next year Wodney we'll be millionaires 

[grouty]

Things are moving on well with the 262 conversion, mainly thanks to Derail 
New barrel is bored 2mm oversize (yep, it gets thin !). New piston from Joe Hooper in Florida. New Megacycle cam on it's way from California.

My question now regards the old cam. I am still using the bike whilst gathering all the parts.
I have made up the alloy plug to fit in the head to re-route the oiling (as done by Megacycle). It requires removal of most of the teeth from the unused tacho drive gear on the end of the cam.
Is it acceptable to cut this gear off completely ?

When I rebuilt the head last week I noticed that the cam was timed up on the KL250 marks. It should be done (according to the book) on the KZ200 marks. I have no idea if the cam in it now is a KL250 or KLX250 one. Is there a difference that would require it to be done to the KL250 marks. If the profile is different between the two could it cause the valves to touch the piston if done to the wrong marks ?
I didn't spot any I.D. marks on the cam, even if I did I would not know which one was which anyway.
Any help would be great.

[JC]

G,

If you go to kawasaki.com you can check part nos to see if they're the same cam. I did it some time ago & 79KZ200 cam was same p/n as 78-81KL250 (#12044 1040).

79/80 KLX250 cam same p/n as 82KL250 (# 12044 1028), but it'd be worth checking these for yrself.

I understand the diff in cam timing is mostly to do w the rpm it will spin. KZ200 revved more. KL250 was sedate trailbike tuning so had milder timing. KLX was more radical & ran the 200 timing which is more suitable for hi rpm. I seem to recall megacycle say use the 200 timing mark.

It would be worth checking clearance issues w Derail. He's done heaps of work on these engines.

If yr KLX is running KL250 timing, it would be even more gutless than std KLX.

I seem to recall Derail saying the airbox needs to be opened up to allow the modifed engine to breath at hi rpm & rev out cleanly.

[grouty]

Thanks JC. What I really wanted to know is.... if I had two cams on the bench, are there any identifying marks to be able to tell them apart. Other than measuring the lift and dwell etc.
Looking through the Zedder software I have it seems that there are quite a few cam part numbers that could fit this head.
I have taken Derails advice and opened the airbox up. I will have to wait until I can ride it up the road to see if it has made any difference. A larger exhaust is also on the cards once the bigger bore motor is built.