i have a complete yoshimura rs-2 exhaust and a k&n air fiter for my 03 400ex but i have no clue what jets to get! ive never done jetting before so i would prefer to get a kit. the problem is i dont know which kit, and which stage i should get. also alot of the jet kits are not coming with pilot jets. i am so lost and i really need help. please give me some advice on what jets to get and or what stage jet kit to get. i dont know if this is the right forum section to post this question but i am kind of panicking as there is limited information on the internet about this. links would be great. thanks for any help, i really need it!

 

My experience is with MC but should be the same. I would start 3 sizes up (my wifes Honda 400 has 142 stock so if the sizing goes 145, 147,150) then the 150 is the choice to start with. With just a pipe change I have never found it effective to change the pilot jet. If your getting a kit follow the directions for a pipe change but the kits I have installed were generally too rich by a small margin. The air filter will likely not effect your jetting. Stage one jetting is all you need, your not changing anything that matters that much. BTW I had a DR650 with HC piston, stage one cam and porting myself, and GSXR1000 exhaust. It ran fine with just 3-5 steps up.

 

Don't know if you'd do it, but a wideband O2 will help you really dial it in. I put an AEM one on my Arctic Cat 500 and was surprised how little I knew. Thought it was running lean, nope, pig rich. Once I got the PMS and the needle on the right clip to get around 12.5/1 or so then fine tune the main jet for the same, you won't believe the difference in power and smoothness! You shoot for 12.5/1 at wot thru the rpm band to get max performance and around 13.5/1-14/1 at part throttle cruising. It will let you know if you get over 14.7/1 as it will start to pop and even stall. Mine has a manual choke, watching the meter, is a big help to tell you when to let the choke off.

 

I hooked up an O2 sensor to my DR650 once and found that my jetting was just right after various tries previous to the O2 sensor. I agree that people usually think their machine is running lean when it is often too rich.

 

Just contact one of the many mfgrs of jet kits and tell them what and all mods that have been done and they will steer you in the right direction with the proper kit. Years back I used a UNI kit, talked to the mfgr and they sent me the recommended kit and it worked great.

 

Well...if you don't have an o2 sensor handy you can always get a baseline with a plug-chop...take a quick run at WOT, kill the engine (while at WOT), pull the plug & read...white (lean), tan (good), black (rich)...don't keep it at WOT for long in the event you are very lean...don't want to burn down the house (motor)...