Jump to content

05 crf250r big bore jetting

Recommended Posts

After experiencing many problems with my build, I finally got it running.

05 crf250r 

05 Head -- re worked head, cut seats, ground exhaust valves. New intake valves, springs, keepers ect. New oem cam shaft, and bearings. Wiseco shim kit. 

05 Carb - running #165 main, #42 pilot, NCVS needle, 3rd clip position. Fuel screw 1.5 turns out. TPS mod


06 Bottom end -  Milled bottom end for Big Bore kit. Hot rods crank and crank bearings. New crank seals. All new oem transmission bearings and seals (including shift drum bearing). New timing chain. New oem center, left, and right case gaskets. New oem shift shaft aka "spindle". Hinson clutch basket. Heavy duty clutch. 

Rebuilt water pump (bearing,seals, impeller shaft), water pump impeller mod. 

New spark plug. New air filter, and filter element. New chain & sprockets. New front tire. Rebuild rear brake caliper. New brake fluids. New grips/ throttle tube. New bearing connections swing arm bushing kit. New all balls linkage bushing kit. New rear shock. All new hardware for plastics, ect. 

I'm still playing with the jetting a bit though, trying to get it really dialed in. If anyone has any suggestions, my altitude is around 800-850 ft.


The jetting im currently running was actually suggested to me from another member on the page. I'm still messing with it to get it dialed in. I feel like im running a little lean.

My altitude is 800-850ft if anyone has any suggestions. Thanks

I also have a stage 1 dynojet kit I could use aswell. Along with the stock NCYQ needle, #172 main, and a spare #45 pilot.


Is the ncyq needle "richer" then the ncvs needle? Think i might go back to oem needle and see how that works. 

I know how to do a plug chop, but this is a fresh engine. I didn't want to start it up and fly down the road at wot. Engine has only been through 1 heat cycle, with about 15-25 minutes of run time. 

The plug is black on the metal outside edge of the plug. The electrode is completely white. I'd tend to think 20 minutes of run time at varying rpm that I should atleast have some kind of color on the electrode. Which makes me think it's running lean. It runs pretty good though from idle to wot throttle though? Obviously I wasn't hitting the limiter.... yet hah. 

What do you guys think? Thanks again




Share this post

Link to post
Share on other sites

All else being equal,  a bigger displacement cylinder and piston will make existing jetting richer.  I have an 04 with an 82mm piston in it.   Mine would like your 162 here at see level and cool,  if it was on good gas.  90 is the best we can do at the pump here.   Yours sounds like it is running clean but slow,  hence the black body.  FYI heat cycling if done wrong can lead to a glazed cylinder (doubtful since yours was probably fresh with a decently honed surface),   and in my opinion has little to gain other than just giving you some easy run time to make sure that nothing is coming apart or leaking.  Richen up the jetting a little if you are nervous though.  No harm there.  

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with: