KJ7687 I agree with your cup of tea.
A typical ride for me here in New Mexico will easily have altitudes from 5000ft to 10,000ft with all types of terrain; which is why I try to jet for 7K. Seems like a good balance. Your 331 is jetted with a DJ124 for 3000 to 3500ft ASL. I am running a DJ122 for a stock bore, which I think is one size smaller than DJ recommends for my altitude. With the 331 bigger bore did you have to jet bigger?

 

Well I think my DJ 124 is a little lean for 3,000 ft. If I wanted "perfect jetting" for maximum power at this elevation, I think a DJ 128 would probably give slightly more power (maybe 1 horsepower) and slightly better "pickup". But I like it so far at 124. It works great at this elevation and I think will be fine pretty high up too. The DJ 124 is considerably bigger than the stock KLX 250S main, which is a Keihin 118 (equivalent to only a DJ 112). I bought the bike used with a Keihin 125 main (= DJ 118), air box lid removed, and a Two Brothers pipe. I went big bore, put the stock exhaust on, put a lid on the air box, and went to DJ 124 (= 132 Keihin) main and Keihin 38 pilot (stock is 35). Admittedly, I'm fairly new to the whole jetting thing, as I've never messed around with it at all on previous bikes. That being said, I've done plenty of research on the subject, particularly as it pertains to the KLX 250S and big bore. I have read that Dynojet tends to recommend pretty rich-side jetting. If you end up keeping stock bore (or keeping it for now, even...), I'd try going down to a DJ 118, and also removing the air box snorkel, if I were you. Essentially, a little more air flow and a little less fuel (since your bike was "running like crap" at 10k ft due to having too much fuel and not enough air flow)... I bet this will work much better for you at 10k, but you won't notice any significant performance decrease at 5k ft. As an added bonus, that should give you slightly better fuel economy, too. If you go to 13/45 gearing on top of that, I think you'd have quite a nice setup. IMO that'd be the ticket for a mostly-stock bike if you really want to stay budget-conscious but still have a great performer. If you go that route, you should be able to put several thousand miles on the stock engine, and then still go big bore when it finally dies and put several thousand MORE miles on the big bore engine. That being said, if you decide to go big bore now, or soon, I couldn't blame you haha... I've had two different 200 cc, ancient, air cooled dual sports before the KLX, both grossly under-powered but still fun as hell lol! Still have one of those and plan on having it for at least another 10 years, maybe forever lol! I just really wanted something with more motor this time. Not because I felt it was totally "necessary" from a capability standpoint, but just because I really WANTED it. I was looking at DRZ's and big DR's, and the XR 400, and a couple others. But ultimately I settled on building a KLX big bore because I'm so pleased with so many other (not power) aspects of the bike that make it better than those other bikes IMO (as awesome as those bikes are!). I'm sure I made the right choice! Honestly my bike felt like it had a pretty similar top end power to what my big bore has now (it was quite peppy for a 250!). Also it would rev out another 2 thousand RPM (compared to the 331), but had nowhere near the power and torque that the big bore puts out at much lower RPM, plus it backfired under decel and was loud as all hell (which I didn't like because I don't need any extra police attention lol!). And yea my Tea is totally the distinguished gentlemen's choice! Haha jk.

 

I think it's kind of hilarious how this thread has majorly gone off topic from my original post, but everyone seems to be fine with that.

 

Sorry about hijacking the thread. No offence intended!

I like hearing about the benefits and issues (power,performance, jetting, build problems) with the 331 conversion, particularly at high altitudes. I am seriously considering following the path of others.

So far the 331 dry sleeve seems to be reported to rev more like the stock bike. Larger bores have been reported to not rev high as easily. The head and valves seem to breath better with the 331. The dry sleeve may not cool as well as a wet sleeve, because material boundaries reduce heat flow. I have not found anyone reporting over heating as the result of big bore conversions. Still waiting for the more information and the result of the water in the oil problem.

Thanks for the tolerance of those who started the thread and others who contributed.
Again no offence intended, it is all good information.

 

Dont worry i dont think anyone is offended. I guess this is the most current thread for you to ask about the 331 kit. If you read this thread thoroughly, you would know i had the 331 installed couple of months ago but am having problems with the bike cooling system. Attempts to fix the problem have all failed so far which will mean i need to remove the head and reinstall the gaskets.

Im pretty sure im the very few guys with this problem but most people have no problems with the 331 kit. Aside from the problem im facing with the cooling system, im still quite happy with bike performance after the upgrade to 331. Maybe you can try installing a pumper carb first and see if the performance suits your needs at high altitude.

 

Yea I wasn't offended at all Capt, and it's "my" thread, lol! I just meant that I think this is a great group of guys, since everyone seems cool with the topic meandering itself way off course And I actually think it is really funny; I never imagined my simple question about big bore engine RPM a couple months ago would turn into a freakin mega-thread with over three thousand views lol!? Funny thing is, I guess I was among those most-qualified to answer my own question (I do appreciate those of you who provided your input on the subject; you did help me, too!).

 

Since we're "on" the topic of "going off topic"...lol, I've been meaning to make a big post with a ton of info about my experience doing the big bore and many other mods on my KLX, and I'm wondering if there's a way it could get a "sticky". I suppose if/when I do make such a thread, it would have to be good enough to be worthy of a "sticky". At the risk of looking like I think I'm something special (I don't.), I think it definitely would be. I garnered a great deal of helpful information from posts such as this (like the big bore installation write ups) when I started researching my big bore and other upgrades, and I think I could offer a lot more helpful information to people like Capt who are thinking of a big bore or other upgrades. While I did find answers to many of the questions I had about these mods, many more still remained unanswered until after I purchased, installed, and used them. I feel like I owe something back to the great community from which I obtained so much useful information. Anyway so the point of all this babbling is that I'm sort of wondering how I should go about this. Really the only reason I think my future post about this stuff would make a good "sticky" is that it would then be easier to find for KLX owners, or potential KLX owners, who want to see what's possible/what works with the KLX 250S (I suppose that is the point of a sticky, isn't it...). I guess I'll just write this thing in a word document or something and then post it on here, and if it's deemed worthy, something can be done. Maybe a link to it on the "front page" or something...

 

That's pretty much spot on in-line with what I know and my experience so far with the 331. It will do an honest 9k RPM if you really want it to (although max power is well below that). That's with the stock carb and bone-stock exhaust and cylinder head. I knew before making my choice (331 vs 351) that the 331's would supposedly rev out a little more than the 351's. That was actually a big part of my decision to go for the 331. I'm glad I did!

 

Finally stripped the engine top this morning to check if it is a gasket problem and this is what i found, refer pictures below by clicking on the link. seems like the leak is coming from the sleeve which is none of the possible problems ever discussed. Must be really bad luck for this to happen and i dont even know how this can happen and how to fix it.

One things for sure, im ending my project with the big bore, it is just too much hassle for where i live, if im in the states its not that bad, now i have to wait for a reply from Bill (i just emailed him and sent him the photos). parts will take about 2-3 weeks to reach and my poor bike have been idle for way too long. i decided to fit back the stock bore and hope my problems with this bike is over.

Anyone interested in buying my big bore kit? im willing to sell it at a loss. It includes the cylinder head with leaking sleeve (which hopefully Bill will fix it at no cost), 2 sets of new cometic gaskets, JE piston with the rings and clips. PM me if anyone interested, if the shipping is below $10, it will be free delivery.

CaptCapSize....interested? Since you have interest in installing a 331, im offering a cheaper option for you with a slightly used big bore kit. the piston is still in good condition but the cylinder head needs to be fixed or replaced.

PicPaste - Big_Bore_Probem1-gFuhqfZ8.jpg
PicPaste - Big_Bore_Probem2-9eqxHWTm.jpg
PicPaste - Big_Bore_Probem3-0vwOVmD0.jpg

 

janov, this post has been going for a bit, so refresh my memory. Did you have any "milky" color to your motor/trans oil during this period?