Boilerplate Setup for CVK > 351cc
 

Is there somewhere already documented a good starting point for jetting the stock carb for BB351? Currently jetted DJ Stage 2; operated at sea level; aftermarket exhaust (fmf)

Lid or no lid?

We had a thread going not long ago about this very issue - the member doing the testing did not provide a final verdict however..

You should start with a totally unmolested and stock CVK - go Lidless and grab a selection of DJ or K jets ( DJ146, DJ148, DJ150 - K160, K162, K165 ) Start with the DJ150 / K165 and work your way downward as you test ride..

I have the 351 and a CVK. Live at sea level, jetting is in my sig. If I can ride easy I can still break 70 mpg or have fun and get as low as 60. Same jetting I had with MCM on stock bore. No hesitation, stumbles, or surging.

My experience with 351 and stock CVK, riding at sea level, mainly offroad:

- after installing 351 changed pilot jet to K38, main to K128, N1TC needle, 2nd notch from the top, KDX snorkel, fuel screw 2.5 turns out
More or less OK but had decel popping. Fuel economy about 50mpg

- changed pilot to K40, decel popping almost dissapeared

- wanted more power :) changed main jet to K140, needle to 3d notch from the top.
Most important thing I noticed was terrible fuel economy, about 30mpg and running too rich

- removed airbox lid, no significant changes

- changed main jet to K132, noticable better performance. Fuel economy about 40mpg, similar to bikes of my friends.
It seems the best and final setup for my 351 - no lid, pilot 40, main 132.

How is your cold starting with those setups?

Why do you ask about the cold starting? Are you experiencing difficulty in your cold starts? My experience with the stock carb is that overall jetting setup isn't the reason that many KLX's have hard cold starting. While one can make it more difficult or improved with proper jetting and air/fuel screw adjustments, a well known issue with many KLX's is the relatively small starter jet in the carb. Oddly not all bikes suffer from hard starts despite the same starter jet. Just bringing this up in case you're issues are related.

Using the N1TC with a 351 is going to be quite problematic - it is too short and too aggressive in the mid-range which is why your fuel mileage has suffered. A K132 does not even get close to properly fueling the upper (over 6k) rpm range on a lidless 250. So I have very good news for you. Assuming you have a performance exhaust on your bike - For a huge bump in power and mileage, reinstall the stock needle and slide spring, and a K165 if you have a performance exhaust system, or a K160 if you just have a performance slipon with the stock header.

Even better, if you have the DNO226 or DNO352 needle from the DJ 2206 or 2152 kit, put it in with the clip on the top notch (1N) and both washers super glued on top of the clip..

Snap, you need to go 1N (top notch) with a stock slide spring, and bump up from your DJ140 main jet to a DJ146.. You should get same mileage but with greatly increased "wow factor" when terrorizing..

P.S. This is the setup I use on my KLX300R with full FMF exhaust system + lidless - I don't have Dyno data on this setup, but it totally rocks.. Your 351 with stock header should "awake" above 5k rpm from where you are now..

Everyone really should stop with crazy/stupid 351 fueling setups. Just because a bike runs "fine" does not mean you aren't killing it or losing huge power, or needlessly getting terrible fuel mileage..

351 + lidless + performance exhaust, near sea level, will need at least a lidless 250 CVK setup with a bump to at least a DJ146 / K160 main jet !

Don't take my word for it, put your crazy 351 CVK setups on the Dyno and see for your self..!!

Had never cold starting problems with both 250 or 351...