BK mod on KTM520...

[motoman393]

Hey Guys,

My friend has an 01' KTM 520 and is getting a 02' in another week! He is very interested in doing the BK mod which is an adjustble screw that controls the duration of the accelerator pump. I have done this mod to about 5 426's and they all work great...but never have done the mod on the 520 with the 1st gen FCR carb! Do any of you guys have any pics or tips? I dont want to mess my friends 520 carb up and would like to get a visual pic (I will post it on my site if anyone has pics)? Thanks,

Garrett

[400jy]

The BK mod does not work on the KTM.You can buy a different accell. pump cover which will limit the travel of the diaphram in the cover. Or you can squeeze the metal fork on the pump linkage to get your squirt time to around 1 sec.The stock squirt is appo. 3 seconds. I did both to my bike and the results are well worth it.

[Jon-D]

Do you get the same effect (performance improvement) using the P-38?

[mxerdom]

What exactly does the bk mod improve?

[Mike_in_Silicon_valley]

The BK, KL, & P-38 mods limit the accelerator pump squirt duration. It makes the initial throttle response much more snappy. You will still need to change your needle though. James Dean is the resident jetting guru. Do a search under his member # and you should find everything you need. Or just ask him.

Mike

[GeoffStahl]

I believe James Dean and Magnum have discussed this previously on either this forum or Holeshot's. Here is a summary of their procedure.

Disclaimer: I have not tried this and it is not my original work, so I take no positive or negative credit for it... =)

Spray duration modification (equivalent of a P-38 Lightning with some adjustment available):

- Take the AP bowl off (it's held on by three screws).

- Center-punched the inside of the AP bowl so the drill bit doesn't wander.

- Use a 4mm set-screw cut to 15mm long (as fine thread pitch as possible)

- Grind and file the end of the bolt/plug square because the diaphragm stub lands on it).

- Using a drill press to keep the hole perpendicular, drill the hole and tap the threads. Run a nut on the outside end of the screw, this will lock in your setting.

- Also wrap the threads with Teflon tape 3-5 times. When the nut is tightened, the Teflon tape sealed up the threads.

- Note, be VERY gentle when tightening, if it strips out, Sudco has replacement covers cheap ($17.50, p/n 021-057).

[Taffy]

i did a superb mod that was so good it was absolutely INCREDIBLE. UNBELIEVABLE, MARVELLOUS!!! so go look at it. it's called the TAPAS mod because it's quick, light, cheap and easy. mine's the one at the bottom. two men have done it now and LOVE it so go to it you lovely little orange men!

Taffy

https://www.thumpertalk.com/bike/ubb/ultimatebb.php?ubb=get_topic&f=3&t=005746

[Steve49]

What I couldn't figure out from some of those previous posts:

What was the downside with a shorter injection time? What do you give up elsewhere in the throttle range?

[motoman393]

Taffy,

What duration is recommended for 520's? .5 secs or what? I will be posting pics and procedure on my site in 2 days or so! Thanks,

Garrett

[joe525]

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[wrsm]

Rest in peace Motoman 393