I have my eyes peeled for a good 300R parts bike or cylinder. I don't want to go as big as 351.

My question is will we lose any of the bike's top end power with the larger 300 cylinder & piston? Does this setup just shift the power lower in the curve?

I have a Q4 muffler, stock header, DJ2148 kit, and KDX200 snorkel.

 

I think this comparison would take a fairly exacting dyno qualification to show precise differences. Honestly, I can't imagine there to be any loss of power at or near redline, and in fact I'd speculate that there's an increase in power across the board from bottom to top. I have the factory 300 top end and had the stock bore with all my mods of complete exhaust, airbox, and dynojet with stock carb. Just going to the 300 cylinder provided noticeable low end grunt, but really I couldn't tell much at higher rpm because of the low gearing I normally run. My seat-of-the-pants assessment in real trail conditions indicated faster revving, more low rpm torque, and sustained power in a higher gear.

Top end power in a single cylinder like the KLX is usually only negatively affected when the displacement increase is quite large to the point where it affects how quickly it revs and/or overcomes the intake capabilities. In the KLX300 cylinder you're only talking about going from 249cc to 292cc, so this is not a massive piston size/weight increase...and it doesn't overwhelm the head, cam profiles, or intake/airbox size to any noticeable degree...at least with the airbox cover opened in the traditional manner and better flowing exhaust.

In my case the OEM 300 jug and piston have been well worth the effort, and it has proven to be 100% reliable for many years. Not poo-pooing the 351, but I like Kawasaki factory reliability and the bulletproof nature of the 300R.

 

Yep. I know the 351s run strong and wouldn't be used so much if they were straight unreliable. That said I want the simplicity and convenience of using OEM parts. I don't know if I can justify $500 on a new OEM cylinder though, so I'm rolling with my 249cc for now.

 

Still tempted to jump on this $130 300 kit: Air Cylinder Block Piston Ring Head Gasket Kit for Kawasaki KLX300 97 08 78mm | eBay

The listing shows 13 sold this year alone. Wish one of those buyers would chime in:




o***k( 33) US $139.991Jul-03-16 09:14:21 PDT y***y( 579) US $139.991May-10-16 01:02:04 PDT r***e( 3 ) US $139.991Apr-28-16 14:27:53 PDT y***o( 0 ) US $139.991Apr-24-16 15:39:33 PDT m***m( 74) US $139.991Apr-15-16 12:07:31 PDT d***o( 843) US $139.991Apr-13-16 05:29:08 PDT j***j( 199) US $139.991Apr-11-16 18:17:23 PDT r***b( 18) US $139.991Mar-30-16 06:50:42 PDT g***a( 25) US $139.991Mar-29-16 18:58:41 PDT p***8( 2144) US $139.991Mar-29-16 12:36:39 PDT h***o( 7 ) US $139.991Mar-27-16 09:45:13 PDT a***e( 0 ) US $139.991Mar-23-16 11:11:34 PDT

 

Well, Bill includes all the parts you need, and although unlikely you will need them, you can order spare parts from him also.

I'd be wary of going with a cheap bore kit (I looked at them also) but decided on the 351 after reading many,many positive reviews.

Now if you are not comfortable with the amount the 351 is bored out, I believe he has smaller kits also.

I also looked at the factory 300 cylinder, but decided to go with the kit because of the convenience of everything included.

I'm sure the 300 would be a great upgrade, but the 351 (especially with a pumper) is an AWESOME upgrade. I've never heard of a owner of a 351 say "meh, it's only a small improvement over stock" lol

 

You can do the carb mod, the airbox mod, the cam mod, the header mod, the big sound exhaust mod & what do you get? 5HP?
Or you can just go with the big 351 and forget about all that other small potatoes. and you get more HP.
It is not rocket science.

 

Well none of that is true, except the rocket surgery.. What is true is that if you have to run the stock exhaust (for sound issues), the 351 kit is your best-bang-for-the-buck.

 

I too went with the factory cylinder but with a Wiseco piston kit. The OEM cylinder was cheaper in Canada than it was in the US (when has that ever happened?) and I sold my 250S cylinder to BB to help offset the cost.
A significant boost across the entire rev range, but likely half of what you would get from a 351. No noticeable increase in vibration. I run a 300 exhaust with a modified end cap.
I have not seen any consistent reports of reliability issues with the 351 so I believe it to be an excellent, proven option.

 

Got a link for that wiseco piston kit?

 

Ebay has lots. Search KLX300 piston. Here is an example...

Wiseco Piston Kit Kawasaki KLX300 97 06 78mm | eBay