Posts
106
Joined
11/29/2016
Location
SE
Edited Date/Time
8/17/2017 1:30pm
Found this "heap" for about 1000$ here in sweden, knocking bottom end but complete and running.
My first idea was to use the YZ250 -02 engine i had, and it lined perfectly with swing arm and sprocket-to-sprocket. But after some measuring i realized i have to cut out in the front of the frame for the pipe (even if i cut of the original mounts seen in picture) , i do a lot of aluminum welding my self but in this case it involves after treatment of the frame and i have some trust issues with that.
So, sold of the YZ250 engine and the parts belonging to it and started the plan to make an 290, with lots of performance parts to make it strong enough for my taste.
Things already bought for the engine:
Athena 290cc kit
Carillo rod incl. piston pin
Hot rods main bearings
yamaha crank pin and bearing
Hot cams stg 2 intake & exhaust
new valves and porting the cylinder head
moto tassinari air4orce intake boot
There will be more things to this list, and everything on the engine will be powdercoated or painted.
Since this is my first dirtbike build, feel free to point out things to consider.
My first idea was to use the YZ250 -02 engine i had, and it lined perfectly with swing arm and sprocket-to-sprocket. But after some measuring i realized i have to cut out in the front of the frame for the pipe (even if i cut of the original mounts seen in picture) , i do a lot of aluminum welding my self but in this case it involves after treatment of the frame and i have some trust issues with that.
So, sold of the YZ250 engine and the parts belonging to it and started the plan to make an 290, with lots of performance parts to make it strong enough for my taste.
Things already bought for the engine:
Athena 290cc kit
Carillo rod incl. piston pin
Hot rods main bearings
yamaha crank pin and bearing
Hot cams stg 2 intake & exhaust
new valves and porting the cylinder head
moto tassinari air4orce intake boot
There will be more things to this list, and everything on the engine will be powdercoated or painted.
Since this is my first dirtbike build, feel free to point out things to consider.
Looks like I got an low c/r piston, but part no. says it's 13,5:1. Maybe it's because the combustion chamber in the cylinder head gets relatively small to the bigger cylinder bore, therefore the bigger volume in the piston top. Someone with experience maybe knows?
Found this little surprise when i split the cases, not much oil going through there! Preavious owner must have ridden the bike without oilfiller cap I think, it was dirt/sand when I felt it with my fingers.
The Shop
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?
I found out where to weld a bung for temp sensor:
I also found out that i can't do anything normally or reasonably, now I had a vision of the bike TOTALLY black with apple candy red engine and matching custom graphics. So this means a whole lot more work, I'm going to sandblast and powder coat every metal part on the bike except the forks that will be re-anodized black. If I can afford it, the lower fork legs will get DLC black coating. Hopefully this will end up really nice, i believe these two colors with carefully made graphics is what need on the bike!
Pit Row
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.
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.
liked so I just went with it:
The ones I pulled out from the engine were marked Japan.
wrap both covers with some transparent protection.
Does anyone have any experience in hard-anodizing the aluminum parts on the bike? I'm going to do all the parts, master cylinders/calipers/ triple clamp/upper fork legs and so on
Post a reply to: 2012 YZ290F black & finished with pics