Bk Mod Duration Timing

[motomike137]

I just became aware of the BK mod for my 01 YZF426. I read about it in a couple different places on the web. The one thing I am unsure of is how to time the fuel squirt duration. Is there some special equipment needed?

 

[flyinguitars]

I think a stopwatch was recommended by BK. I just eyeballed mine...it was about 4 seconds stock. Also, make sure the squirt doesn't hit the slider. Check around at www.thumpertalk.com in the 400-426 forum, there is alot of info about this mod posted there, including links to pics of the mod.
Mike

 

[Blue Thunder]

Grab a stopwatch and click it when you twist the throttle and click again when you see the squirt stop. Time the duration down to .3 to .5 range. Do this with the throat of the carb away from the jug and stuff a rag so the fuel just goes into the rag. There is also a screw for timing up above the new screw that you will drill and tap for. Once you have completed the mod, take the bike out and do some testing, if you are getting a bog or hesitation, adjust the timing screw in 1/4 turn increments. Jetting..I went 1 richer on the needle clip and bumped my main to a 165-168 depending on temps. Your fuel screw becomes a big player here also, tweak on that to get the response fine tuned to your right hand. Good luck, Jason

 

[wayneo426]

Right on BT

BlueT- I have a question for you: Does the BK affect anything other than off-idle situations?
I liked my mid w/ the ELN needle better when it was one clip richer, and supposedly I will have to do that after I do the BK mod. What do you think?

 

[motomike137]

Feedback

Thanks for the ifo. I am looking forward to trying it on my bike. I also plan on adding an exhaust sytem, maybe the DR D setup.

 

[Blue Thunder]

Mike..save the $$ for tires, chains/sprockets..you're gonna need them!! I have not researched the Dr.D pipe but nothing else out there really makes much of a difference for these bikes. Learn how to use the power this bike has stock and you can win races or just play really hard.
Wanyeo..I feel the BK helped run my bike through the midrange faster and harder. Say if I'm in 2nd gear steady throttle..just where it is purring and whack it..it just jumps right into the midrange and revs out quicker than stock. I just like the way it pulls. I am running the stock pilot and 1 richer clip on the stock needle. Scott Wheeler and I have not been able to switch bikes since all of his changes and mine so it would be great to feel out a WR w/the YZ timing and all of the carb mods you two have done.
Also, on the BK, it seems to have lengthened my ride time regarding fuel consumption, my stock squirt duration was 2.7-2.9 seconds..that's a lot of fuel being dumped. Now at .5, it is just more crisp, starts better and is a better hot starter also. For as cheap and easy as this mod is..all 426's should have it done. Good luck w/it. Jason

 

[yota]

forget the stopwatch. just try timing 1/3 second with a stopwatch. what you need to do is push down on the top of the accelerator pump rod on the rt side of the carb until you just feel it contact the diaphram. run the screw you tapped in up to hold it in this position and then back the screw off 2 1/4 turns (fine thread screw). now go to the screw up above the new screw on the same side of the carb. this times when the squirt of fuel from the pump starts. hold the throttle wide open and set the gap between the screw and the black plastic cam to .6mm. the last step is to set the idle properly. most people set it too low cause when properly set it sounds like it is idling too fast. set it to where it sounds too fast and then back it off just a bit. this really helps starting. do these 3 things and your 250f (what I have) or 426 will start easier, have awesome quick throttle response and get way better gas mileage. keep in mind that some of these carbs are spraying gas for up to 4 seconds every time the throttle is turned (mine was 2 sec.). thats a lot of difference from 1/3 second. you may need to richen your needle position after this cause a lot less gas will be going into the engine.