Alright I've been reading tons of threads so far. As the KLX300 is pretty much sold out for the year, I'm looking at a couple 2018+ KLX250's with EFI. I'd want to throw a big bore kit on it - any of the 300/331/351 would do. However, I'm worried about tuning the EFI to run properly with the big bore. I've read countless threads from owners/tuners in both North America and SE Asia that have had crazily mixed results, going with API and EJK and others - it doesn't seem like there's a single solid solution, even though the bike has effectively been out since 2009. There seems to be tons of issues with tuning the fueling for some reason - and I don't want to go and spend $5k on a used KLX only to end up dumping hundreds or thousands into a big bore kit that doesn't have a solid chance of running properly.

Am I missing something here? Is there a tuner or ECU flash that will get a big bore kit on the KLX250 to work properly? Or do I need to just shell out the $7k for a new KLX300?

 

Countless? Where, if I might ask? B & B says they have solution on their webpage, I've seen videos on Youtube of other folks with EJKs that seem to be working. Just a note: EFI didn't hit the US until 2018. I know some other countries began getting it in 2009, but the US lagged, and US developers definitely got a later start. Your profile doesn't mention where you are from.

 

In case you don't know:
You buy the KLX351 EJK fueler, install it, set it up as per its' instructions, enjoy..
If there are any problems, EJK will solve them for you.

You may want to recheck the threads/posts in here of members that have done exactly the above with great results..

Your welcome..

 

I recently fitted Bill Blue's 351 kit to my KLX 250S EFI bike, with EJK controller provided with the Bill Blue kit, and for everyone's benefit I can share my sad experience with it: bike hesitates to startup which is one problem, but even bigger problem is that reving up to 6-8k rpms and releasing throttle it dies out. My mechanic and I spent 3 hours trying out all sorts of EJK settings, but no chances of resolving this problem. I contacted Bill, he was quick to pick up the phone, but couldn't help me on this, saying he's not a fan of EFI (what kind of answer is that for someone distributing EFI kits?). Contacted EJK asking for recommended settings on the controller - no response. I tried raising rpms, taking airbox lid out, unplugging stock exhaust to see if any of it helps to get rid of stalling issue - nothing helps. Having spent ~1000 eur on this upgrade (I'm in Europe, so customs taxes are applicable), and 300 more for mechanic work, I just wanna cry for being so naive! For those of you thinking of fitting 351 kit on KLX250 EFI, consider other options out there.. perhaps 292cc upgrade might work better, I hope.

 

Hi,
my 2015 klx250 has been upgraded with the original 292cc Cylinder and piston , bigger 260cc 12 holes injector , full free exhaust (lambda in place) and a 2,5 kOhm thermistor in series to the original to add slight more fuel.Run EXACTLY like original without fiddling with any added electronics........

 

Thanks for sharing such useful information.
Could you post a picture of the kind of thermistor you bought and where you installed it?

Your novel approach makes total sense. An increase in displacement is a constant, so the fuel demand will have exactly the same overall profile just shifted higher. You have eliminated the need for a fuel tuner.

 

Hi all….. I have a klx250 EFI as well and am going to increase the displacement as well.

just looking for the best road as it seems many have had issues.

this solution using a 2,5 kOhm thermistor is curious to say the least and I’d like to know more.

ive thought about getting the ecu flashed or using a pcV with auto tune as well.

 

I can’t find any instances where someone got a 351 working properly with EFI and 351 and EJK.

There is a YouTube channel and he briefly used the Ejk but he switched to PCV and auto tune.

if anyone successfully pulled it off I’d love to hear from you as it seems only 331 has worked with EFI from what I’ve found with my searches.

 

Then you missed Jeffs youtube page.. JH Motor Club - https://www.youtube.com/channel/UCBV...yrjkj3iOf6Os0Q

He accomplished exactly what you are asking about. All details are available on his page.. And his "experiments" gave us a bunch of useful info about everything connected to EFI 351's - such as the HP limit of the stock injector ( 27-28 hp, which is about what a "uncorked" 351 will make )..



Also, Jeff is a member - I do not know if he keeps up with the forum postings.. @J Higgens

 

292CC Cyl with 260CC/min inj is like original 249Cc cyl coupled with 220CC/min inj, adding free flow exhaust with KDX200 snorkel and a twin air filter and slightly more fueling is needed.
A 2,5kOhm NTC thermistor in series to the original IAT NTC fitted inside the airbox fool the ecu thinking a colder air is actually sucked (near 10°C colder) adding a little more fuel to the mixture (5%).