Damn Snap, that post gave me a nose bleed.. Probably an aneurysm too..

 

Just an update. I was a bit hasty on starting the thread. The turn around time with Bill Blue is a bit longer than I thought. Hopefully I'll have the kit by Monday and I can throw it back together. In the meantime I've changed the brakes, grips, and sprockets and chain. Now I just need a complete engine.

 

Spoke to soon! Just unboxed my bb kit. It's stamped #626. Ill have it running by tomorrow morning with first thoughts!

 

I just got my 351 together yesterday and will do the break-in with the carb settings I have. Then may tinker with them after seeing how it runs when opening it up.
By the way, my bike fired up right away after getting thing buttoned up. Sounds great and can hardly wait for break in to be done.

 

After being deferred for easter festivities, I got the bike back together last night. I decided to leave the 35 pilot in the carb for the initial run. I did my first heat cycle and the head pipe was glowing red after a few minutes. I decided that was way too lean so i skipped the 38 and threw a #40 pilot jet in and ran it again. I can't see if the pipe is still turning red, but it seems to run fine with the 40. I haven't tuned my air fuel screw due to the location of it. Does anyone have any secrets to adjusting that screw while running? Also, as per the manual, I'm supposed to run it until my fan comes on. It hasn't come on yet and everything seems pretty hot. is there a way to see if coolant is actually flowing through the engine? Would I be better off just buying a new thermostat to be safe? I'll make more updates when i get the seat on the bike and take her for a rip to see my mid-range and top end and give a final conclusion on the 140 or 144 main jet and needle position.

 

With the #40, you have to set the fuel screw to midway between idle drops. Not easy to do but you only have to do it once. Alternatively, it seems that 2 turns (+-) out is where most of us end up - near sea level.

Again, if your bike was still a 250, it would require the following:

Lidless airbox,
DJ144/K158 main jet,
DJ needle set to top notch with both washers on top of clip (super glue helps with this..)
Stock slide spring,
Stock slide lift hole/port.

Know ahead of time that if you don't get the carb back together properly, especially the diaphragm sealing, or otherwise foul a circuit with debris, you'll get a malfunction that you'll blame on everything except your "wrenching" - the KLX250, modded like yours, runs great with a lidless airbox and main jets/CVK setups, ranging from DJ132/5N to DJ150/1N.. (5N=bottom notch , 1N=top notch)

If this happens, just take it back apart right quick and fix the issue - don't run your new 351 on a faulting carb any more than necessary.

IMO, the above setup should give you power unlike any other similar BB351, with the possibility that WOT above 6k would be better fueled with a DJ146, or DJ148.
FYI: For several years now, my '07 KLX300R is running mods like yours and a DJ146/1N CVK setup with eye popping results - second gear power only wheelies!

 

I've been trying to figure a way to adjust that screw without cooking my hand on the pipe. Ill place an order for a 146, 148, and 150. It seems you've done enough research and haven't steered anyone wrong. I want to squeak as much mid to top out of this bike as I can. I wish I had the cash to put the bike on a dyno, but for the horsepower, it doesn't seem to be worth it. I haven't got to ride it with the bb351 yet. Maybe this evening.

 

You need this.

FS-2

https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.koubalink.com/fuelscrew.html&ved=0ahUKEwih0oiQ_KvTAhUE8WMKHQRqAs 8QFggmMAA&usg=AFQjCNGE_cZS4NiRvBcUI1GPUBkPNH5NAg

 

Here is my "tool"

 

I just think its really interesting that if you look at "the spreadsheet", most people with 331 or 351 kits are running 128 or 132 main jets with either stock 35 or 38 pilots...

I realize klxster has more dyno time than probably that whole spreadsheets worth of people, but i do think its interesting that so many people run 128 or 132 and seemingly work ok. Klxter i sure wish you had a big bore kit to dyno...

I think i'm going to get a wideband AF meter when my kit gets here