Matt's KDX 225 Alaska edition!

[Chopperpilot]

Ok, took the bike out today for it's first real ride after a few heat cycles. The Millennium Technologies 225 big bore kit is pretty awesome. I assumed the bigger bore would run a little richer than the 200, so I went one size smaller on the PJ and MJ and swapped in a CEK needle in place of the Airstriker's DEK needle. I'm not sure if I magically hit the tune button on the head, or just how awesome the MT BBK is, but WOW!
The bike is an explosion of throttle response at any point any where. Not 100% sure on the complete tune yet because I haven't actually held it WOT in gear yet..... because um... well it's really really fast! No bog, no hesitation, no where. Well, actually if you're 2 gears above where you should be and whack the throttle, it'll give a little pause. I ended up riding a gear higher than optimal just to help me control engine response.

Now the 2003 YZ250 front end.... Pretty good. I lucked out and these already had Gold Valves in them. These are 46mm USD KYBs that have a 'not sought after at all' 32mm cartridge in them that MXers did not care for. The 2003 version was the last year Yamaha tried the 32mm mid-valve set up (it's terrible because it has to flow a ton of fluid through it), and these had about 2.5mm of float in the mid-valve from the factory. I think these with the softer base valving with Gold Valves, work pretty great for trail use compared to last years 93 model KX 43 USDs (which I had slightly softened the valving and really liked them compared to the factory KDX front fork). I feel like the front end is even more planted, stable, and steerable than the 93 KX setup. Hitting rocks, roots, or ruts and I feel I was getting less deflection than last year. So I guess the bigger 46mm forks and the significantly stiffer axle mounting setup (compared to the 93 KX) makes a difference. I'm using the same tire and KX wheel as last year so that hasn't changed. The YZ triple trees have a solid cast handle bar mount which probably also helps out with the preciseness feeling. I didn't feel the solid mount was too rough or vibraty.... but this is only one ride.

I also Gold Valved and rebuilt the rear shock ..... and what can I say....... it feels like a shock! I'm shockingly sensitive to forks on motorcycles and mountain bikes (I re-valve my mountain bike forks too!) and apparently I'm shockingly insensitive to rear suspension on both (as long as they don't rebound too fast!). I do think the rear has better traction and feels more stable, but I'm also dealing with a whole 'nuther level of engine power now and can't really feel particulars about the rear end. I think I might also have put a little too much preload on the rear and I'm sorting that out now.
I also put a LED front light on and it works fine with the stock lighting circuit, seems to be very bright..... but in Alaska, dirtbike season correlates with not ever needing a light season so I don't know how well it lights up the trail. I am having a slight issue with the throttle/cable. I ran the throttle cable back in a was that was relaxed and can move freely, but the bike will slightly rev up with a full turn to the right and a couple of times it seemed like it wanted to hang the revs a little. Can I just lube the throttle cable? new PWK return spring? new throttle cable? (I'd probably do the KX throttle if I did that)

[Chopperpilot]

Ok, put a few more rides on the 225BBK and the revamped suspension. Here's the take away. Still blown away by the motor, it makes it easier to ride trails faster. Which brings me to the other take away. The suspension is much more planted (front and rear) than ever before. I'm having to continue to adjust clickers because I'm riding faster and faster over rough roots and rocks on single track. I found I had to slow the rebound on the forks a little bit and on the rear shock too.
I remember the factory front end (and the previous 93KX front end) both getting 'easy to induce' headshake above about 53mph. No change with the YZ 46mm forks. Is this what other people notice too? It doesn't 'have' headshake, but hitting a frost heave on the road at 53 and above, gets the forks going a little wiggly fairly easily. I have the forks up in the triple trees about 10mm (probably..... it's a line on the tubes I lined up) so I might try dropping them and see how that works. No complaints with how tight it will turn! one of the reasons I'm cutting through the trails much faster.

[KDXGarage]

Thanks for the updates. I am glad it is working out for you.

[Chuck78]

I think your high-speed issue is due to the fact that the KDX geometry, both the steering rake and trail being quite steep and quick, in conjunction with the short wheelbase, are more conducive to very rapid agile nimble handling in mid-speed and technical slower woods trails, and sacrifices a bit of high speed stability - giving you that twitchiness above 53 mph as you noted. Running an extra bit of chain length to keep the rear axle further to the back will slightly improve this, as well as decreasing the preload on the rear shock spring to allow the steering to get raked out ever so slightly, but the geometry is such a drastic departure from the modern 300s which are limousine length with lazy steering angles, that you will never achieve that type of high speed stability or hill climbing stability. The trade-off is that when I ride with guys on 300s who are my age or even 10 years younger, just avid recreational trail riders, not racers, they always have trouble keeping up with me (I'm not a racer so much, either) in the mid-speed woods trails, because the KDX is so much more agile and nimble than the modern bikes with heavier rotating mass engines (more gyroscopic effect on those bikes makes it harder to change direction) and longer wheelbases and lazier steering, the KDX is much easier to whip around corners and around trees, obstacles, etc. The KDX changes direction much easier due to the lighter reciprocating mass at the engine and no added weight in a balance shaft or big heavy piston, bigger crank and rod etc, as well as the shorter wheelbase + quick steering geometry.
One of the guys that's always trying to keep up with me commented, "dude, you just float that thing through the woods, it's all I can do to keep you in sight!"

[Chopperpilot]

It definitely changes direction fast, this weekend I glanced the front wheel off of something in the trail (never could tell what) and next thing I know I'm pointed 180 degrees around the way I came! Without actually crashing, woohoo! I was running at a pretty good clip for how tight the woods were.

[Chuck78]

Hi matt, we haven't heard back from you for a while since you initially got the Big Bore kit and the KYB fork swap install. How's this thing running?

I just put an email into Gary at Millennium inquiring about 220 cylinder porting versus starting with a 200H cylinder to go big bore, and remember that you have the Millennium 225 kit done to I believe a KDX 200H cylinder.

I may try and pick up yet another cylinder, and see about having porting done by 3 different prolific two-stroke cylinder porting experts, Ted Boyko @ Boyko Racing, Tom Morgan Racing Engines, & Gary Braun @ Millennium. I might even see if I can get another one going if I can pick up another decently priced use cylinder, via Matt Denecke / Denecke Racing Technologies (the YZ400 guy), former lead fuel systems engineer at Lectron and former owner of Apex Technical Innovations making two-stroke cylinder heads. Matt & Gary are both younger than me and younger than the other places I would send my cylinder for porting, and I feel it's critical to both capture the knowledge held by these seasoned veterans as well as using these younger very prolific cylinder porting wizards as in a few years they will be the veteran guys remaining after the other is retire....


I hope all is well with you, and hope that you got to ride your KDX a fair amount this past summer up there in Alaska!

[billie_morini]

Chuck said, "I just put an email into Gary at Millennium inquiring about 220 cylinder porting versus starting with a 200H cylinder to go big bore, and remember that you have the Millennium 225 kit done to I believe a KDX 200H cylinder."

Chuck, ask Gary what Millenium use for that KIPS packing seal when a ustomer pays for KIPS cleaning and re-assembly, please. Last year, their sales guy demonstrated he is lazy, a liar, or both.

[Chuck78]

I can ask if they replace them, but I'm sure they are aware now that that part is no longer available. Either they use a silicone o-ring or an X-Ring of the dimension we have now which Fredette sells/uses, or else they just clean them and reinstall them, knowing they are no longer available and not an industry standard size.
I'll very likely have Gary do up one of my cylinders, I just wondered if perhaps he preferred starting with a 200H cylinder, as I would like to get three different cylinders ported from three different cylinder porting wizards to compare. My friend already made a video comparing the Boyko Racing porting vs the Mitch Payton/Pro Circuit porting and related cylinder base and cylinder head work. I have a ported cylinder done by a shop in Canada although I don't feel it is as good as what Ted Boyko or Tom Morgan Racing Engines or Pro Circuit would do with porting, although the port timing appears to be relatively stock still, the knife edging techniques and the more enlarged intakes versus the other two are telling me that perhaps this was a less skilled boarding job, although it in my eyes and the opinions of others is definitely better than what Eric Gorr or the well-known KDX mechanic and racer of notoriety does in terms of porting. When I see you backwards knife edges on the port dividers, with a knife edge facing into the air flow, the opposite of how an airplane wing works, I know that the porting is less than standard understanding of porting principles. Especially when some areas are opened up substantially larger. You can really hurt performance by enlarging things too much in certain cases as well as removing too much material which increases the crankcase volume which has a large effect on obviously the crankcase compression and performance.
Now I'm wondering if another benefit of machining the base down on the KDX 200H cylinder is not only to lower the port timing so that they can enlarge the ports overall, but also to decrease the crankcase and intake tract volume slightly so that they can then take port material off without enlarging the crankcase volume greater than stock...
I am by no means well versed on porting, but I am doing my best to learn some basic fundamentals, but not enough to go out on my own and start grinding on cylinders extensively. I will however do work on cylinder heads here when I get more free time to make up a jig for the KDX head to mount in a lathe, that's a lot easier to quantify the results and the volumes, clearances, squish band width etc.