Bk Mod: How Do I Get It Right?

[BIRDDOG]

I just did the bk mod,and it has cured 90% of the bog.I still got a little there when i crack the throttle hard.No matter what way i go on the screw its still there.Also is there a better way to time it,the stop watch just isnt consistant. I got .80 to .45 in the same test.
the eye to hand delay is a problem.I also raised the needle one clip like many of you had suggested.

 

[Boozer]

the stop watch is very consistant. It's the operator that is causing the inaccuracy! not having a go or anything, but what's the best reaction time a drag racer can hope for? i think 0.4 seconds is a very good reaction time!
Anyway, some people use a video camera and film the squirt. They then replay the film in slow motion. Some cameras work by 'frames per second', and the duration can be worked out that way, but i doubt it needs to be that accurate.
Some bogging will still occur when smacking the throttle from idle, no matter how much you adjust, but did you adjust the pump timing screw? Small adjustments here can make a big difference. If it doesn't bog when riding, then i think it's the best you can hope for.

 

[colorado-high]

I had the same problem. I leaned the fuel screw between 1/4 to 1/2 turn and the bog went away.It is still there when you wack the throttle wide open at idle but when I ride there is no bog.

 

[NH Kevin]

If you punch up www.thumpertalk.com, this topic is addressed almost daily!

 

[Hick]

Originally posted by BIRDDOG
Also is there a better way to time it,the stop watch just isnt consistant. I got .80 to .45 in the same test.

I never bothered with the stopwatch for the reasons you describe. I measure the travel at the pushrod instead. I got the best results at about 1 mm of travel, about 1/3 of stock. That way you can set it up without any gas in the carb and no watch or video camera is needed.

Also, I think most people find that additional pump delay is a necessary complement to the BK mod. On my ’00 and ’01 I ended up ¼ turn in over stock. That is on the adjusting screw attached to the pump mechanism up by the pulley.

Hope this helps.

 

[JB]

as bk himself said, if you don't change the main jet, you've only done half the mod!!!!

 

[wayneo426]

Dont forget the needle!

While your at it, change your stock needle. I went with a ELN in addition to a larger main, (168). I really do feel a nice increase in performance. The mid is far snappier, and the 3/4 range is SWEET!!! :)

 

[wayneo426]

Dont forget the needle!

While your at it, change your stock needle. I went with a ELN in addition to a larger main, (168). I really do feel a nice increase in performance. The mid is far snappier, and the 3/4 range is SWEET!!! :)