2012 YZ290F black & finished with pics

Sounds like a cool build, looking forward to the pics.

Nice project.

I had a Athena 290 kit on a 2010 Yamaha, had a lot of blown head gaskets with it. It did make a whole lot of bottom power. Do you plan on using other cams etc?

that oil screen never seen one that bad. looking forward to this bike build.

.

Thats a nice porting job on the intake side. Ben a while since I've seen the valve guides cut level with the runner. Nice!! With your colours why don't you anodise the engine black and get some Red anodised wheels and recd accents in the graphics kit and a few red billet pieces here and there?

I built a 2007 CRF280 with the exact same setup only I scored a brand new Tom Morgan full on race head ported with xelydine (sp) valves for the bike and my god that bike felt like what you'd expect a modern 400 to be like if that makes any sense.... I ran a stage 2 hotcam to keep the power spread out, had one of those low boy full carbon can single sided exhausts on it and maaaan that bike was unreal, lightweight with big bike power .... I hope yours turns out as good as mine did Bec it was the perfect amount of power.

Oooo a black anodized engine looking like one of the 80's Yamaha TT bikes white with red accents would look pretty badass though ... I'm sure this bike will be badass when done!

Mine went from your typical 250f screamer to a MEATY feeling torque laiden monster! It felt like it revved, i dont want to say "slower" per se but more like it had a flywheel weight (which it didnt) or like it had a ling rod kit installed (also didnt have) just that i got the sensation there was SO much more fury between each and every stroke i can remember that feeling of that engine with a huge smile but its hard to put into words. I can say withput a doubt I gave up NOTHING to a 2007 CRF450 bec for the slight difference in HP the bike fully made up for it with lighter weight and if you want ultra responsiveness you'd be good to run a 100/100 or 90/19 I cant remember tye exact size but whatever rear tire size 250f's first came out with when there were still 125's around. The bike was a lot faster than a YZ400f and the powerband felt a lot like a very healthy 250 2 stroke very similar to a 2003-up YZ250 if i were to model its characteristics. Maybe that gives you an idea of what to expect, youll notice some increase in engine braking too which i came to like nothing gnarly but noticable.

One thing you want to be VERY aware of i found with mine it had a Voracious appetite for the air and fuel mixture not that it got drastically less tank range but jetting was critical, pay EXTRA SPECIAL attention to jetting at 2/3 or 3/4 throttle to max flat out throttle because ultimately thats what did me in and the reason i had to sell the bike after breaking my back. Obviously the larger combustion area draws more fuel but with the shorter stroke of a modern 250f engine at 12,000 rpm you want to make sure theres always enough fuel being delivered up top bec most the time at this throttle position youre usually about to be clearing a sizeable jump or tearing ass through a pretty gnarly section of track or trail and a chop of the throttle to snapping it back on WOT will suck the normal amount of available fuel right out of that carb. Not the entire float bowl but the amount the carb would deliver to a even well jetted 250f. Its strange, you wont experience any engine performance symptoms of it being lean or not getting enough fuel we made every attempt to get rid of the infamous "Honda bog" my generation of CRF250's were known for and we were very successful except of this ONE time it wasnt that kind of a "bog" though there was a split second hesitation of nothing from the engine and my body just like KR94 and Bogle was positioned to weight the bike and articulate it through the arc of a jump as i was on the face of a full blown peak to peak 60' double when it happened which resulted in my own Kenny moment. My rear wheel stepped out at the last second i chopped the throttle, brought her back in line and hit the throttle and .... nada. Mind you this all happened so fast i was already going ass over teakettle before i realized that i was fooked!

My best advice (this was NOT a main jet issue we were spot on there) would be that youre dialed with the accelerator pump and leak jet in the carb maybe over compensate just a hair as Its prob a little difficult to replicate and adjust for since there isnt a lot of data on jetting a 290f in the upper echelons of the RPM's its important to know and compensate for the larger draw with a big bore engine spinning that fast. I remember now, i had put a reducer ring in the carb for the Honda Bog which cured it as a 250f Bec it was really bad and after like the first ride as the mighty 280f we (me and a buddy whos a top level mechanic) Stock, the 06&07 crf250's carbs were too big with a stock engine but juuuust right for a big bore. Sorry for the novel but i just want to make sure youre 100% successful in the ONLY part i missed with my bike. Like i said its not something youre gonna experience doing garage revs, roll on tests or at wide open throttle even when chopping and getting back on the throttle but if theres ONE thing im greatful to pass along as advice youre not likely to ever hear, its this, although you're on a Yamaha which if I remember didn't have this problem much if at all so this advice could be all hot air and i dont want to make it sound all doomsday just something i would've been so thankful to know when building that bike, it even had RG3's full anno & DLC Diamond kit suspension 18mm shock shaft... this bike was, in a word BITCHIN' ... i miss it and im gonna look for some pics ill post of it too.

Ahh I'm remembering every ride on that bike now..... You'll have the exquisite handling of a 250f and the punch and pull of a 400/450 without the obnoxious inertia or weight that even if you had an ultra light 450 you'd feel since it's a characteristic of the larger moving parts of a 450 in gemeral if your comment above IS what you're looking for then I have no doubt you'll be all smiles, it was the perfect bike. I've ridden the earlier KTM350's I think the second year Model that came out and my bike was lightyears better in engine raw power and handling. I can't wait to hear how much you'll like it once you're done. Don't rule out the idea of a flywheel weight if it still feels like a 250f the power will be there and the stage 2 cam should maximize it BUT just in case. I remember I went from the stock 51 tooth rear sprocket to a 47 and the bike had zero problems pulling it and made the trans gearing/spacing perfect for the increased power. It sounded so throaty and healthy too a real head turner when I'd be on the gas.


OH DONT FORGET to install stiffer aftermarket clutch springs. I used the Tusk ones and they were GREAT! My clutch never slipped and lasted me till I sold the bike.... Gawd I regret that now but unfortunately I had to.

Cool color on the cases.

wow.. that is different.. will the painted clutch cover hold up against scratches from boots?

Don't wanna bomb your thread with a heap of pics of my bike but have a look at my build thread. I got almost every aluminium part on the bike done in black bar the swingarm, rear suspension rocker linkage, Cylinder and a few other things. Theres a fair few pics on there, they start at around page 4 or so if you don't wanna go through the whole lot. 2008 RM125 Rebuild.