BK mod problems



11 replies to this topic
  • Wicked_Crash

Posted June 03, 2002 - 08:03 AM

#1

OK, I did the BK mod and I timed it at around .34sec (that's like from now to now, like nn,...it's really quick) and I made sure that the squirt just missed the carb slide. I still have the bogg when I snapp the throttle wide open, so am I missing something or is this as good as it will get? Any suggestions?

  • S_Phillips

Posted June 03, 2002 - 10:08 AM

#2

Check your Pilot Ciruit.

What PJ/PAJ do you have?

Is it a consistant bog or does it pop sometimes?

  • Wicked_Crash

Posted June 03, 2002 - 11:32 AM

#3

The bogg doesnt happen when I roll open the throttle at a moderate speed, it only happens if I go to WOT in one swift movement. It is so bad that the engine will die if I don't let off right away. I do get a little backfireing on deceleration, but it is mostly when I let off the throttle going down hill. I am using a 148 MJ, 38PJ, stock PAJ, stock needle @ #3 (Taffy said to get rid of the backfiring, lower the PAJ or get a PA screw, but the dealers here don't have a clue about what a PAJ is, and have never heard of the PA screw so I haven't done that yet.)

  • Hick

Posted June 03, 2002 - 04:03 PM

#4

Originally posted by Wicked Crash:
The bogg doesnt happen when I roll open the throttle at a moderate speed, it only happens if I go to WOT in one swift movement. It is so bad that the engine will die if I don't let off right away. I do get a little backfireing on deceleration, but it is mostly when I let off the throttle going down hill. I am using a 148 MJ, 38PJ, stock PAJ, stock needle @ #3 (Taffy said to get rid of the backfiring, lower the PAJ or get a PA screw, but the dealers here don't have a clue about what a PAJ is, and have never heard of the PA screw so I haven't done that yet.)


Wicked,

I hope you aren’t trying to eliminate the “my bike stalls in neutral if I whack it open” effect. If you can get the kind of response that allows you to (feel like you are going to) loop it in second from zero throttle and below-idle rpms (no clutch) then you obviously have set things to respond to the fastest roll-on you will ever see in riding situations.

Anyway, you didn’t say if things improved with the limited pump or not. Did you try to advance the spray timing?? If it is “just” missing the slide you may improve things by delaying the timing 1/8 or ¼ turn in on the “other” screw. I’ve ended up w/ some amount of delay on all four bikes I did the BK mod to (’00 & ‘01YZ, ’01 WR).

Finally, while a lot of people believe you cannot separate the two, I think you may need to address your jetting before you expect to cure what ails ya with the BK mod. Point being it is not a panacea, just another tool to adjust what the carb is delivering to your motor.

I don’t like the stock D taper needle in the 426 (unless you leave the exhaust insert and airbox lid on). I have done a few jetting exercises on friends’ WRs and IMO the E (YZ) taper needle is always an improvement, even at a place like Rampart, but perhaps I’m biased because I own a YZ. Also, even though you are at altitude, a 148 main is terribly small, particularly with the stock D taper needle. It is a wonder any fuel is escaping what little space remains as you come onto the taper. That right there could even be contributing to your problem.

Lastly, while I have not tried this on the WRs I mentioned, which run great, and so don’t really understand how it works/what is affected, it could be that your air cut valve is another contributor to the decel popping. I would think a 75 PAJ is a good match for a 38 pilot and wouldn’t create the popping you are experiencing but I would have to say that from what I DO know about the air cut valve all bets are off (as far as the PA circuit goes) until you disable it.

Hope this helps.

  • S_Phillips

Posted June 03, 2002 - 04:42 PM

#5

yes I highly recommend plugging off the vacuum hole that activates the ACV.....this leaves the white spring loaded valve inside the carb open at all times.

This has been the only way I've been able to get consistant reading at the bottom....

Some people have plugged the vacuum hole off and snipped the tip of the plunger off. I tried just turning the diaphragm around so it wouldn't push the little white valve inside open. But with my bike if the white valve stayed shut there was still no consistant readings........

terrible design.......... :)

  • Wicked_Crash

Posted June 03, 2002 - 05:09 PM

#6

Hick,
I'm not really worried about eliminating the “my bike stalls in neutral if I whack it open.” That's not a big deal to me (yet) because I don't find myself doing that on any of the trails that I ride. I like to leave my options open though, so I was just curious if there was something more I could do to eliminate it maybe in the future. Thanks for the E taper needle tip, I'll have to see if I can find one. So far with the 148 MJ I the bike has not shown any simptoms of being too lean, there is awesome power throughout the throttle (except for the whole bogg thing). It may be too lean if I go down in elevation, but I do 90% of my riding between 8000 and 14000 feet. The plug is burning clean with just a little bit of soot around the edges wich I think is showing up from the bog and backfiring. All in all, I am pleased with the setup I have, but I like to mess with tuning my bike just to see what works the best for me. BTW could you explain plugging the vacume hole, where is it? I don't have the manual in front with me right now. Thanks again Hick and S Phillips for the tips.

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  • LarryCO

Posted June 04, 2002 - 04:50 AM

#7

Wicked,
I "almost" have the same setup...without the same symptoms. Change out that 75PAJ to a 65PAJ...and get an EKN needle...see what happens. Better yet, call Sudco and order a pilot air screw/spring combo (a 65PAJ is 1/2 turn out equivalent on the screw if I remember correctly). I went into Excel Yamaha (Colfax and just west of Wadsworth) and got my EKN there. If I remember correctly, it was listed under a '01 YZ426.

Given that I havent played around with a stock needle (is it a DRR for an '02?), I cant say much about the combo you're using...only that the 38PJ/65PAJ/EKN#3/150MJ/160MAJ works awesome for me.

Larry

  • Hick

Posted June 04, 2002 - 10:19 AM

#8

Wicked,

I like Larry's advice and recommend you try his setup. From what I've learned w/ my pals' WRs at Rampart and my YZ at other high elevations corroborates Larry's more complete setup.

Yes the EKN is an optional YZ needle, but I think you may have to look on the '00 fiche to find it. A similar needle, ELN, is, I think, available on the 250F fiche. The ELN would be 1/2 clip leaner than the EKN but identical otherwise.

Unfortunately anytime you mention YZ needles you have to warn folks that on the '00 fiche all the needles are mislabled with a V in place of the K. So if the flunky behind the counter insists you are ordering a EVN, not an EKN, just smile reassuringly and maybe pat him on the back or stroke his hair while you assure him everything will be okay...

...because what arrives will in fact be an EKN.

As for the Air Cut valve, do a search on those terms and I'm sure you will uncover the whole scoop on what it does and especially how to disable it.

I'm glad I own a YZ and don't have to bother with all these valves, plugs, lids, octopusses, stops, lights, bells...

  • LarryCO

Posted June 04, 2002 - 10:56 AM

#9

FYI...part number for the EKN (Hick says on the '00 YZ fiche) is 5JG-14916-EN. Dont let 'em tell you it's something different.

When you pull out your stock needle, drop me a line and let me know what it is (out of curiousity...mine was a "DRR").

Late

  • Wicked_Crash

Posted June 04, 2002 - 12:17 PM

#10

Thanks for the part # Larry. I have to stop by Excel Yamaha on my way home to get the universal mounts for pro tapers so I'll get the needle while I am there. If I remember right, my stock needle is a DRR, but I'll let you know when I switch. I'll check out the ACV mod when I replace the needle.

  • Mark_Cantrell

Posted June 04, 2002 - 02:01 PM

#11

Wicked,

I'm sorry I'm so late to this. You have too little AP squirt. .34 is not nirvana. Go longer. Turn it out until you can whack it without coughing or dying. See 'AP 101' on the 250F forum.

Don't try to jet away an AP problem. You'll end up way too rich at steady state.

Good luck,
mwc

  • S_Phillips

Posted June 05, 2002 - 06:34 AM

#12

Mark

Don't try to jet away an AP problem. You'll end up way too rich at steady state.


I've been trying to get mine right with littl APJ
as well. It just seems to need it. I dunno maybe it's programmed into the CDI :)

Wicked Crash

BTW could you explain plugging the vacume hole


If you pull the cover off of the ACV(its on the side of the carb) you will find a spring that pushes a diaphragm with and needle pinpoint on its end this pushes a valve(white in color)that's inside the carb. Just below and left to the spring, is a vacuum hole that actuates the diaphragm. Also to the right of the internal valve is a hole that leads to atmosphere.

With the cover off you can start the enging up
and plug up the vacuum hole,, manually activate the white valve and see how it affects your engine while idling.

I would like to know where the other side of the white valve leads to myself. So I can understand the mechanics of it better.

All I know is with me running a PJ of 35, PAJ of 55, white valve open all the time it runs fine. If white valve is closed all the time I get a popping(not backfiring) at the 1/8 to 1/4 throttle position.

If I let the ACV work like its supposed to do each ride will be different.

BTW - I not a carb GURU, I am however an tinkerer
:D




 
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