Thanks NB! I was juz tryin to help answer some ?'s. I'll probably be doing the 350 after i figure out my taxes!

 

That 350 looks sweet. If I still had my KLX, you all know I would not be able to resist the call of the 350.

 

Thanks so much for the mod list, Nobrakes! If we were on TT I'd give you a +1.

Well even though Bill is going through extensive testing, and it seems OK... I still worry about such a thin setup. I have a 4 year loan on this bike, I'd hate to burn it up in 3. Cost is another factor.

Like I said, I'm pipedreaming (no pun intended). Full Muzzys is next on the mod list, behind a set of Fatbars and a Twin Air.

EDIT: Holy crap! Well, I guess I won't be doing a big bore conversion until I hit the numbers. $478 to do the 300 setup. Ouch.

 

The bottom end of the KLX 250 is strong enough to go to a 450.

To make the bike a bigger displacement you remove the cylinder & install one that has been bored out to a larger size. The big bore cylinder kits all come with a new piston, pin, keepers, rings, head & base gaskets nothing needs to be done to the bottom end.
I haven't had any heating problems with the 351 kit.

 

Im a bit confused, I just remove my 250 Cylinder and install your one that has been bored for the big bore kit, thats it? I dont have to get any parts of a KLX300?

And another thing I wanted to ask is, are there oversized pistons available in case the top end needs to be rebuilt? Can the Cylinder Be bored out again or do I need a sleeve?

 

Yes, the outside of the cylinder remains the same, just the inside is bored and sleeved to 351cc, and a larger piston of course. You need no parts from a 300. As for the rebuild, you could probably get oversize rings and bore the sleeve .010 if you needed to. Bill would have the answers, as I have not seen this 351 kit yet.

 

At this time there are no oversize pistons offered for any of the big gore kits.
You will need to send me your old 250 or 300 cylinder for me to bore & install the big sleeve or you can pay me $125.00 extra & you can keep your cylinders or I will charge you $125.00 core charge returnable when I receive your cylinder. I use one of my cylinders ship it to you, then you send me your cylinder & I return the core charge money to you.

 

Oh ok.. This is so tempting!! Sad thing is I'v got no money on me these days! :'( .. Bill, do you think the top end of the 351cc kit will hold up as long as the stock 250?


ddt, thats interesting.. I thought I need the 300 Cylinder hehe..

 

This is strictly my own opinion; I'm not speaking on Bill's behalf or representing him or anyone elses' work with these bikes.

Modifying motorcycles is a pretty technical business; the information is shared all over the Internet of things people do, like the "free mods" and clear on into stroker kits and hot cams along with carb swaps and high flow pipes.

An individual does need to learn all they can about what they are getting into before they do anything mechanical to their motorcycle. A pipe change alone is something that if not done correctly can melt a piston, from too lean a mixture, for example. I've seen these things happen. It's not the pipe's fault, it's not the manufacture's fault, it's not even the owner's fault. It's an information gap the owner didn't realize he was into, but the result is the same; a ruined engine, a very unhappy owner, and lots of money to get back to square one.
It's real easy for new riders to think they just need to "bolt on" what everyone else is doing, and get into real trouble because they don't have the knowledge of engines it takes to do these things and also the little tweaks and adjustments and testing it takes to get it right.
We all started somewhere with this kind of work. I just see it as a different degree of modifications to your KLX from changing your handlebars, adding handguards or adding a shark fin to protect the rear disc. The instant a person removes, for instance, the airbox lid, and says, "all I have to do is add a jet and I'm hopping up my bike," they have crossed over a completely different threshold of "modifications."
I've been in this business of motorcycles and machine work (I am an engineer in aircraft manufacturing) and engine work my whole adult life, since 1971. I've made more mistakes than Bayer makes the aspirins I've taken while I learned my way through things. I've seized up a dozen bikes by doing stuff like breaking rings when I installed my "hopped up design."
All I'm saying is, engine modifications are not always just simple bolt on issues, and you're good to go. Lots of fine people on this website and a hundred like it share terrific results, have great luck putting together mod combos of carbs and pipes and jetting changes. But it's STILL a science to getting these things done and done correctly. Buy a kit for something, say a better shock; don't torque the right fastener correctly, and one day, bang, you go down hard and break an arm because the clevis weld failed on the front shock mount, because the bolt was loose, and the shock has been bouncing around in there for the last year. Take any 3 bikes that have had a pipe put on them? from Harleys down to a Honda mini-bike, I'll wager $20 that 2 of them aren't jetted correctly, and are ridden that way forever.


For the guys out there that are working on their bikes for the first time or the 20th time, there is more knowledge out there on about airflow waves and flame propagation within the combustion chamber, and dwell configurations, and on and on, that are affected by just removing the airbox lid.

One of the habits I gained from an old-timer back in 1971 when I first started working as a parts counter kid at a bike shop was this: Learn to buya soda pop for the local mechanics, LOL. You want to learn all you can about engines before you ever turn a single bolthead.

Thanks for listening to this old-timer, guys. I just wanted to mention my opinion of these things. Discussing the fine points of big bore kits from a non-technical background can really get bogged down in misinformation and guesswork, it's some slippery stuff to take online opinions and use that as all the guidance one needs to understand what they are getting into... There's an absolutely the "right thing" to do, try and learn all you can about doing things. I'm not sure a few sentences on a moto-list is really going to educate very well.

Just my $.02 worth, and that's all it's worth. Have a great weekend. I'm going to ride my BMWF800St as much as I can stand in this cold assed weather.

 

The way I look at the engine to simplify things is to break it into THREE sections:

Top end: Head, valves etc. Bolts to the top of the cylinder

Cylinder: (jug) The cylinder is the middle part of the engine. It is bolted to the bottom end. The cylinder size and piston are what determins how many cubic centimeters of displacement you have. The bore size of the cylinder HAVE to match the size of the piston so these items are the SET you would get if you went to a bigger bore. The inside of the cylinder has extra meat that can be removed (bored) to make the displacement (CC's) greater. Bigger jug, bigger piston, bigger power.

The bottom end is where the crankshaft and clutch reside.

Going with a BIG BORE KIT, 300, 331, 340 or 351 entails removing the head (top end), then removing the cylinder and ( I'm assuming) popping out the wrist pin in the existing piston and removing it. Then attach the new oversized piston with a new wrist pin ( I'm assuming) and "slide" (yeah,....slide) the piston back up into the cylinder. I'll bet this is the tough part. The new piston rings will need to be compressed to "slide" up inro the cylinder. Once the piston is back in the new bored cylinder it's bolted back to the bottom end then the top end id bolted back on.

I'm sure there are tricks to make things easier. The idea of putting on a bored out cylinder and keeping your stock 250 piston would make installing the piston MUCH easier but I 'm pretty sure you would lose alot of compression and develop a HARD knock if you did that so it's not recommended.

If this is not correct somebody chime in.

MY QUESTION:

A 300 kit can be purchased from Kawi and is basically a 300 jug and cylinder from a KLX 300. What's the cost.

I agree that if you are going to go to the trouble you might as well get all the bang for your buck so the 300 kit seems too tame.

The 331 kit. I know nothing about. What's the cost?

The 340 kit I've only recently heard of. Fingermullet has the 340 I believe. What's the cost?

The 351 is new but sounds the COOLEST and is the biggest.
What's the cost?

Bill can probably answer for the cost of the 331 vs 350.

I'd like to know the cost of each (DIY. No labor included) for all 4 choices.

My question