As most of you know I've installed the 300cc kit on the KLX and I love it. And while it's great, I'm also looking to increase that even more, but there is concern about how high one can / should go w/regard to reliability, etc.

Also, I've got my Keihin FCR carb on order from Four Stroke Works and have spoken to Jerry there a few times. Jerry used to work at Stroker along side Larry Roeseller who were the defacto KLX experts. Since I already had a customer relationship with Jerry on the new carb, I e-mailed him and asked about the big bore stuff.

He gave me a phone call back yesterday and we spoke at length. Basically, he said that the KLX engine is built very tough and reliable and going to 330 or 331 (Jerry does 331 with his kit) is not an issue. You are not going to destroy the engine unless you really abuse it. He said the guys that have problems are the ones that run it wide open all the time and basically run it like an MX bike and don't do the usual MX bike maintenance such as frequent rebuilds. As long as you are using it in normal off-road duty and not MX racing, it will last forever.

With regard to the higher bores such as 364 or 380, he said he can do that. But he recommended replacing the crank because of the stresses involved, and that gets a whole lot more expensive since you need to ship him your whole engine and requires splitting the case. He said that our transmission gearing is pretty close in with the crank shaft and the clearances are not a lot. The extra stresses of the very large bores may cause some flexing and perhaps some interference which is one of the factors in their "Stroker" engines back in the day on the KLX300. But for 331cc, that is totally not necessary.

Anyway, I know there is interest in this by others here and I thought I'd pass along the information I have. When I do mine, I'm going to have Jerry at FSW do it since I already have that relationship there and I feel he really knows his stuff and I trust him. Also, he said he can do it without me having to remove my 300cc jug - I could just send him my old one when I get the new one installed and that way I won't have much down-time.

 

Now if only your bones could be fixed up as quickly as your bores!

 

Seriously! Hey, I got my arm through my shirt sleeve today ... that's progress

 

Hmmm... Very interesting..... Thanks for passing the info on. Did he, by chance, mention any prices?

 

Sorry, I didn't get an exact price, but it seemed comparable to what Kustom-Kraft was indicating - around $400 to $500, not including cylinder.

 

What you are saying here makes much more sense to me than the other thread dealing with this subject. I was under the understanding that the 250 was simply an underbored 300. So, when someone said that you had to use a 300 cyl to go 330, it did not make sense to me.
When you go 331, do you want to sell me your 300 stuff?

If not, maybe we could work up a good "group buy" price on his 331 kits. I will be doing SOMETHING this winter. I will have 5,000+ miles on the bike by then and I will not feel bad about a rebore.

 

Just to be clear, the 250cc cylinder is not an underbored 300cc - the water coolant passages have a different profile and the wall thicknesses are different on the 250 vs the 300. This makes the 250 cylinder inappropriate for overboring - at least that's my understanding. You do still have to get the 300cc cylinder if you want to go to 331 or higher.

And yes, I'll be happy to offer my 300cc cylinder + piston + rings for a good price. They are in excellent condition, only lightly used

 

But didn't you say in the last paragraph of the first post that Jerry can overbore the 250 jug?

 

No - what I meant was that Jerry has 300 cc cylinders at his shop and he can bore out one of those, get it treated and ship it to me with the piston, rings, etc. When I install it, I take off my old 300cc cylinder that is currently on my bike and ship it to him and then he'd refund a portion of the total. I wasn't meaning my old 250cc cylinder - sorry that wasn't clear. The only benefit to me is that I wouldn't have to first take off my 300cc cylinder and send it to him since that would result in quite a bit of down-time since I think the process takes a while.

 

Boy, you are a wealth of knowledge today. Thanks. I guess it wouldn't be worth discussing since you have to send the 300 jug to him? I was thinking that I would purchase the whole deal so it would be ready to install minus gaskets. I know you do not have too many miles on it but I am edgy about installing a used piston in a new cylinder.
Maybe you could send him the 250? LOL....
I am amazed that Kawasaki bothered to case two different cylinders for these bikes. What a waste of time and resources.