YZ 293cc Athena Kit

First off - I have no experience with this Athena kit.

I think the Athena kit used to be a GYTR-certified product, however.

This came out after I had gone the Eric Gorr YZ295 "mo betta" route on my 2006 YZ250. The EG kit was a ton of hassle and nearly impossible to jet. At the point I had enough and was uninstalling it, I saw the powervalve parts were scored (it was erratic powervalve action that I had been battling with jetting). When I finally did get a hold of Eric about this later (10th+ call likely), he was extremely non-chalont about it and agreed to buy the kit back (I think I was in to it like $900 at that point). I later learned he had low-cost labor assembling these kits at times and I think I got one of those kits. I wasted soooooo much time on EG's kit and moved onto 4-strokes after that. I think EG went onto work at Millennium Technologies after that, but then something happened. EG is one of the funkiest guys I ever done business with and it ended up costing me a ton of time. Seems like a nice enough guy, just really struggled with communication and didn't empathize with the problems his (his assemblers?) craftsmanship caused.

Why share the above? If you end up wondering if the EG YZ295 kits/cylinders are good, my experience is nope, too risky - a real crapshoot. That said, I do know people who were really satisfied with their YZ295 kits. So I really think I just got a bum one. It still pains me to this day that I never got it to run right, as the 300 kit has so much potential.

Also, if you have jetting issues with whatever YZ250 2-stroke big-bore kit you go with, don't forget to investigate the powervalve as a first step. It could save you a TON of time.

The above said, and being aware of the options out there now (Gorr, ESR, Athena) I'd go this route if I was to do it again ... which I might:

Millennium Technologies MSPEC kits:
https://www.millennium-tech.net/serviceInfo.php?id=19

And Tom Morgan's influence is the primary reason:
https://www.millennium-tech.net/vidplayer.php?id=35

I work in product development and what I feel happened with Gorr and Millennium is that Gorr's design was good, but his execution became spotty given manpower issues. There's an art to getting something into production. And it's far from easy. Gorr was outsourcing his cylinder work, in part, to Millennium. Millennium *seems* to have been sufficiently impressed that they started a partnership with Gorr, but then something happened. I am not sure what that was, but now Tom Morgan is involved and the same basic Gorr kit is being offered by powerhouse Millennium. I think that YZ295 kit is now in its prime and you'll be backed by one heck of a team if you go that route.

I appreciate the EG report on the YZ295. My bike is also a 06 YZ250 and be thinking about a big bore kit again. I did some research regarding Eric Gorr 295 kit, as it has a great price at $660 bucks and uses your existing cylinder. Good info about the jetting issues, and again its your experience with EG. I know their is several kits but looking for something reliable.

I have a athena kit, its pretty good, I had some minor porting done to it prior, nothing major it worked well, jetting was easy, added some low end, just was in process of rebuilding it and everything looked fairly good after 50hrs, I have a pretty good 250 cylinder stock bore that works well, its pretty much a toss up between the two, one works well here and the other is good in different areas, depending what your looking for there are some good tuners out there that have the stock bore figured out, reliable and parts are common.

I updated my thoughts above after reflecting a bit more.

Kristen_Valentino is spot on. "There are some good tuners out there that have the stock bore figured out, reliable and parts are common." I'd find one of those guys. And I am suggesting Tom Morgan is one with a high-end shop behind him.

Thanks for the info guys. I got my 250 running really crisp and clean. Mods are minimal, fixed the head squish, timing advanced for my liking, FMF Fatty, and running 51 tooth. The bike runs strong, and was thinking more towards 300cc cant hurt. I mostly trail ride and ride intermediate to expert level. I appreciate the input, suggestions, and will help with my decision.

Keep us posted! We want to hear about you going hog wild with a 300, Smart Carb, custom pipe, A-kit suspension, etc.

If it was me I would send the 293 kit to Morgan Racing if I wanted a big bore. lol.

My EG300 was a pain in the ass, always chasing brass.
Best thing I did was get a really good low to mid port job on my 250. Shorty silencer and gearing.

Know you said no to esr, mine was great for 100 or so hours....like the simple pv set up.

I'm leaning towards the Athena 293 kit if I do decide to pull the trigger. The ESR kit has that simple PV setup, which i don't care for along with steel cylinder sleeve.

^^^ I checked into Nikasil plating the ESR bore. It can be readily done. Millennium Tech was the source if I recall correctly.

ESR owners may like to know that.

The athena kit is pretty good, compression is a little high, I feel its a better route than the EG setup, cylinder is designed for it, they run good stock, uses o rings for head instead of gasket, quality is pretty decent overall

Rider 5280 wrote:

^^^ I checked into Nikasil plating the ESR bore. It can be readily done. Millennium Tech was the source if I recall correctly.

ESR owners may like to know that.

PowerSeal USA does really nice plating on multiple surfaces. I have personal experience with their YZ 285 big bore. Absolutely fantastic work and ran very well here in Colorado mountains. I have also had a Kustom Kraft big bore KX 250 (295cc). That bike ran extremely well and work was high quality (it was almost as strong as my old KX 500). Look at both of their websites as they give costing up front.I do have friends that use Athena kits on Yamaha 125s and 250Fs and they work well. Good luck!

https://www.kustom-kraft.com/

http://www.powersealusa.com/