Hi everyone,
I am considering options for a big bore setup. Has anyone ever used a KLX300 piston by boring out the 250 cylinder and having it re-plated and honed to mate with the 300 piston? There is a company here in eastern PA that will bore and re-plate the cylinder for $250 and the cost of the piston, rings, and gaskets is around $150 so that would be a low cost big bore setup.
Thanks, Mike

 

But you can buy an AHL 299cc big bore kit complete for $180 on Amazon. A few riders here are running them. I still have one in the shop to put on the bike this spring/summer. It is a Chinese clone of the KLX. Only thing a few have done is go to a Kaw head gasket and piston circlips, others haven't. That is definitely a low cost big bore. I bought mine on a special when it was $152. Just gotta get a week where I can do the work all at once, don't want to string it out.

 

Wow, that is actually cheap! At that price, it would be worth experimenting with, maybe just checking compression every 1000 miles or so.

 

Mike, there’s not enough meat on the cylinder skirt(which extends into the cases), to bore to 300 cc.
There are occasional KLX 300 cylinders for sale on eBay.

 

Oh, I was wondering if that might be the case-thanks. I really want to build a torque monster so I'll probably just go with Bill Blue's 351 kit. I used to ride and race 125, 250, and open class two stroke MX bikes and I always preferred the torque type power of the open bikes so I may as well go for the 351. Like the owner of the shop we raced for in OKC would say "If you're going to go for the bear, you may as well get the Grizzley".

 

If the money's there, no reason not to go there. If you have EFI B&B has the necessary ECU to make it work. If carbed you can jet the CV, go to Bill's reworked 34, or do a TM36-78. General jetting is known to an extent.

 

I agree, I pm'd Klxster for his advice for jetting the stock carb but I'm not sure he is all that familiar with respect to jetting the BB 351 setup. If not, Bill can surely advise me and I'll go from there. I may also install a set of "woods grind" webcams, which I am waiting for confirmation which actual grind number they are so I know how well they will work with the 351 kit. Since 90 % of my riding is in the sand of New Jersey and tight technical eastern PA rocky, root infested, trails with lots of water, I want a torque monster engine. Thanks for your input klx678-how do I purchase one of your cam chain tensioners?

 

Bill's answer how to setup stock carb was very simple
I don't mess with the CV carb I don't know what size the jets are, I recommend changing the jets as follows
Increase the pilot jet one size larger & Increase the main jet two sizes larger than what ever nets you have in the carb at this time.
Thanks
Bill

But you can find a lot of useful info here in the forum.

 

Thanks-this site is very helpful. I can't wait to get my 2012 model on the trail with the 351 kit!

 

Guys, the information is in here - where 351 owners have verified the use of my lidless CVK setup (with DJ148, DJ150 main jets) as being a great solution.

During dyno testing and development, I ran my 250 for quite a while with the lidless setup and a DJ150.. So any that are interested can see the fueling offered by that setup on a 250 - but the really interesting bit is that the 250 runs absolutely perfectly with the lidless setup and a DJ150. So much so that I left the setup in the bike for quite a while (even after the Dyno test indicated very rich fueling at WOT) because it was so much fun !
Main point is that the lidless CVK setup with a DJ150 offers a known/charted/tested fueling curve that works perfectly and makes smooth biggy power..

Here is the real problem, that has been proven over and over. A 250 or 351 will run perfectly fine with horrible fueling. This means an owner would never know how much power they have lost, how much fuel mileage they have lost, or how much danger their engine is in. No doubt due to bikes that seem to run "perfectly fine" , we have very little dyno data proving proper fueling on the 351.

For instance Kwak: From his signature line, he is running a setup that does not properly fuel a 250, on his 351 !!!! A DJ132 on a lidless airbox cannot flow enough to properly fuel a 250 at ANY rpm with ANY clip setting on ANY needle. The short, aggressive N1TC on the 3rd notch allows the DJ132 to do all it can, but it is nowhere near capable of creating an acceptable AFR.. Yet I am sure his bike seems to run "perfectly fine" with AFR's that likely range between 14:1 and 16:1 during WOT ops !!!!

The dyno testing on the 250cc with DJ132 with lidless airbox and DJ DNO228 needle with clip on the 4th notch down could only produce a best of mid 13's to 1 with most areas at or even over 14:1 . This and much more data is on my threads below..