290 kit for a 08 RMZ 250

I've picked up another 08 rmz 250. The first one was for my son thats riding a 250cc expert (MX/trails combo) and a 13 to 29 yr "A" class. He is standing third in one and forth in the other. now, I really like his (stock w/ T4 exhaust) rmz so I got me one (used 08). Now I'm thinking about a 290 kit mostly because I'm standing about 250lb. Need a little more bottom end so that I can change the gearing to get more speed.... I ride mostly trails w/ a little mx ("C" class) thrown in... How would the 290 kit do???

What kinds of changes would the jetting need????

Would it need cams w/ the 290 kit to really pull me around????

instead of putting the 290 why not just change the sprockets and if that doesnt work change the gear ratio in the tranny???

I ride an 08 rmz250 To me 3rd gear is to high an 4th gear is so low. Im going to try an play with the sprockets an gear ratio. IMO a 290 kit would be installed after i blow it up an have to do an engine overhaul. In dry conditions the bike is a monster but in loamy stuff I can not compete with 450s


There is a guy named Mike S. that installed one on an 08 when they first came out. Maybe he can chime in with some advice. If it pulls down low anything like my yz290f did, you are in for a treat! I had to lean it out quite a bit. I also had a flywheel weight that helped it lug even more.

Good luck to you guys this weekend, wish I could make it. I am pulling for Sheldon to take the championship. You and your wife have raised a fine young man. Good Job Dude.

Mark V. #421


Thanks for the kind words.... He's hopping all of the football training will help with his riding. He's pulled tires (24" truck tires) 40 yards over 1000 times over the summer..

They've got him as a 165 lb center and has held his own.. Tuff kid even if I say so....

You will have to go leaner on the main. We found the stock cams works very well, tried Yoshi cams along with 290 kit, stock cams worked better for us.

The Yoshi pipe really runs well on along with the BB. It brings some of the lost top end back again, along with overall gains. We tried the Dr Dubach, it only gives the bike top end.

I think the best options if you BB is a pipe and a good head job. The RMZ heads need to be filled along with the port job, contact Ron Hamp on this.

Lastly you could consider a Hot Rods stroker (+3mm) along with the BB. We run this and it works well. All though we need to balance out the crank after the first test run, it wasn't properly done from the factory, and make the bike/engine vibrate.


The 290 BB makes a noticable differnece through out. Although mine is still a bit flat up top without an aftermarket exaust. Aftermarket exaust is an improvement for both the stock bore and the BB. My 07 has 25 hours on the Athena 290 kit. I really really like the added power. I don't have to wind it up as much before the engine starts pulling. Makes it more 450ish with the handling of a 250. If I don't get a different bike this winter I'm probable going to add the stroker crank because I've been so happy with the BB.

Stock main jet is a 162. I'm running a 160.

My gearing is 13/50. That gearing works well for me. There are lots of threads recommending the 13/50 combo.

Forgot to mention that I'm running the stock cams. Engine wise everything is stock except for the big bore kit. Including the exaust system. The only reason I know an exaust system will improve the BB is because a friend has the same bike with a big bore kit and LeoVince exaust. His pulls at higher RPM's where mine signs off and I have to shift a little sooner.

Thanks guys.. This was what I wanted to hear....


Hi Guys

I got the 290 and a 250, no comparision in power, I run a 13 tooth in the front and 48 in the rear and it wheelies in 3rd and 4th without pulling on the bars. I tried a few differnt jeting configurations, I am not the best on jetting but I am happy with 40 pilot, 160 main, stock needle postion (3rd). let me know if you find something else your happy with. I run a DR D pipe and recently switched to VP U.4 and it runs cooler and stronger. I also run a coolant recovery bottle, a 100% necesity in the woods. I like the RLR model but Motion pro has a nice one too. Feel free to contact me anytime if you have questions.

I will be at the NV and AZ National Enduro rounds next month if you will be in the area and want to try it. I could not be any happier with the power output.

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