I am a technological moron, but enjoy learning. At present I am trying to learn why my KLX 250 is overheating, and what to do about it. I'm hoping that some of you more technically savvy guys will point me in the right direction. In simple language.

The problem is somehow connected to a big bore the was done recently, as it was running fine before. The big bore is not so big - up to a modest 300cc with a re-sleeve. The local mechanic in Chiang Mai who did this also recently did a big bore with another KLX 250. I think he does good high quality work - he is very respected here for his work with (mostly) trial / trail and Enduro bikes of all types - Beta, KTM, Yamaha, Suzuki etc. I had a ride on the previous KLX big bore he did, and loved it! That bike has since been worked hard in the mountains, and on some long road trips, with no problems.

However, that was a carb version, which is what he mostly works with. He said he didn't have to change the jetting, just some minor adjustments to f/a ratio. Mine has EFI, so this may be the crucial factor. It is the mechanics first big bore with EFI, and he is unsure what the cause is.

What my bike does:
1. It starts easily, idles ok.
2. It hesitates on initial acceleration, then takes off.
3. When rolling off the throttle the engine braking seems much stronger than before.
4. And it is running HOT! I now ride with my right leg off the footpeg. The radiators and coolant are fine. The fan cuts in more often then before too (I guess that this is a good sign, in that the thermostat is working).

Can anyone suggest what the likely cause may be? And of course, what to do about it? Does it simply need a larger injector - and if so, can I use the injector from a Versys, which someone suggested is intended for 325cc, so should be an easy swap, and would simply enable the ECU to provide a fraction more fuel? (This is my preferred option, as even I can manage to swap the injectors over!) Or do I need a new ECU? Or something else???

 

Overheating as in the light is coming on and shutting down? or the bike is just running hot? My recent 351 Big bore run around 68 degrees C thru the top end... from what I understand below what the fan comes on at...


mine is carbed tho...

 

Your probably running lean... look around the forum for EFI mods. Most (& I) have a carb here.

 

No, not shutting down. Running hot (and a little rough). I notice because I can't leave my foot on the right foot peg anymore because of the heat, and the fan does work more often to cool it down. Most people in this forum with big bores seem to have carbs - probably a more practical conversion as easy to play with fuel/air mix.

 

I did look around the forum - and a number of other forums and websites - but could not find an answer to my specific issue. As I noted, I suspect the problems are because it is running lean. I would like to know if just going up a little in the size of the injector will solve the problem , or must I bite the unwelcome bullet of trying to learn all about re-mapping, ECUs and piggyback controllers?

 

There are some guys here with EFI and big bores of various sizes and tuning experience documented a bit in various threads.
Try a search for EJK controller, big bore, and this forum on google.

 

Nothing to do with injector size. The injector works perfectly on a 331.

Your bike is running very lean there for hot without a piggyback controller. EJK is your best bet & easiest to use choice. EFI - Electronic Fuel Injection Controllers - ATVs, UTVs, Motorcycles, Snowmobiles, Scooters, Sport Bikes, Watercraft, these available to buy in BKK or ebay. A power commander PCV will also work very well but is a little more expensive.

Tutorial: EJK Controller Unit Functionality

Be careful not to put a hole in your piston with prolonged hard riding at high rpms!

This thread goes on forever but very informative towards the end....https://www.kawasakiforums.com/forum...-klx250-36083/

 

Thanks Joel - you are a gem! I'll now spend some time educating myself about the EJK.

 

Most people on here with big bores are from the USA. The KLX is Carb only here and there are a few manufactures that produce big bore kits in the States.

 

Possible point, the engine is likely not what is running hot enough to be a problem with your leg, otherwise your left leg should be getting it too. Did you put a pipe on the bike? I have a 650 and with no guard on the header, the heat is near unbearable without boots. I got it ceramic coated and now far less issue. The little stock guard will reflect some of the heat away, it's surprising the difference.

You should also make sure the coolant system is purged of any air. I believe that can cause over heating issues. The bigger bore may likely produce more heat, but consider when the fan is coming on. I don't remember ever having my 250 on, but I've not really thought about it or gotten in a situation where it would happen. On the 650 I have. The fan comes on in slow/go traffic where there is little movement. It also comes on when I get into some tougher trails where the same happens. Runs for a bit, then shuts off when all is good.

One consideration for cooling in general is the Thermo Bob that allows better coolant flow around the cylinder although it likely won't do a thing when at higher operating temps. It uses a bypass system like all auto engines have, allowing the pump to circulate coolant around the cylinder even when the thermostat is closed. Better more uniform cylinder temps.