Help Bike bogging problem

11 replies to this topic

Posted December 17, 2001 - 12:06 PM


Please Help!!!! This last weekend I was able to do the famous "BK" mod on my trusty stead.
I had assistance from "Mad Potter" (TT name) and I would like to thank him for his help and everyone here for thier input. Now on to the real problem....

CURRENT SETTUP:. I am running a PC-T4 exhaust and with the standard Pilot 2 turns out,stock Needle settup, BK mode .3 or so spray time. (By the way it does not bake fire on deccel) I currently have a 158 mainjet installed do to the fact I ride at 5400' or so.

THE PROBLEM: The bike rips from 1/2 throttle up when moving but when making a slow turn and getting on the gas it about dies? I was practicing on clearing some table tops and as I was about to land I would wick the throttle to unload the suspension and the bike would just about stall out completely in the air!!!! Talk about a scary moment when it about launched me over the bars!!! I checked to see if anyting was in the bowl that could be blocking the main but nothing was to be found? I tried moving the neddle position thinking it was not getting enough gas but it made it worse? So I called it a day. Once I got home I pulled the plug it was BLACK!!! I had just installed it yesterday too when Mad potter and I fouled one ( Ooops :) )
The plug looks carbon fouled--It looks as though the gas is burning but like there is just to much fuel??? I thought when you did the BK mod you had to increase the mainjet size for the lose of all the extra fuel.

I only thing I can came up with driving home is the float bowl height is off? Does the float bowl effect this problem? And if so which direction do you adjust it?

I would greatly appreciate any help I can get.


Posted December 17, 2001 - 12:09 PM


PS: Sorry about all the typo's I was in a hurry.


Posted December 17, 2001 - 10:04 PM


Hey Pokey,
I wish I knew what to tell you, I sure don't have any bog with mine. All I can say is try the same jetting I have and see what happens. 160 main, 45 pilot, 1&1/2 turns on the fuel screw, stock needle and clip position. If you still have a bog with those settings then hopefully someone with more knowledge will help out. How did it run overall? Could you feel a difference after the mod? I find it very strange the difference in how these bikes perform even with the same settings. Sorry it didn't help, I was hoping you would be grinning ear to ear after we did the mod on your bike.


Posted December 19, 2001 - 07:03 AM


Thanks MAD POTTER, I am going to pull the carb off tonite and try to reset everything. I will try your settings and see how they work as a base line.

Again thanks for you help.

  • Jason_in_KC

Posted December 19, 2001 - 07:40 AM


Hey Pokey...have you adjusted the timing screw for the AC pump? It is the screw up above the BK screw you just faces more toward the back of the bike. Anyway it controls the timing of the squirt..take the black cover off of the carb, grab a screwdriver and take the bike out..adjust that screw in and out in 1/4 to 1/2 turn increments and see if that made a difference on mine! My .02.

  • Fastest1

Posted December 19, 2001 - 08:22 AM


I know this mod has been temperamental for some, but I cant figure out how going up a jet size will help! I did not change my mj at all. In fact after experimenting with lowering my pilot to lean it out on the idle circuit, I am finding tha t I had it dead on before the BK. It just made it a little crisper. This mod makes no sense on why it should work but it did seem to improve starting and lessened my plug fouling. Good Luck

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Posted December 19, 2001 - 02:33 PM


Jason and Fastet, thanks for the input. I am going to adjust the timing screw tonite and pray is does not snow here :) so I can test this weekend.

The reason I was thinking of changing the MJ was the dealer told me he tossed in a 158 but much to my surprise when I pulled it out is was type of jet I had never seen. A 150RD is what is was and I have no idea what it meters at?? Hell the dealer could not even tell me what the equal jet was. Yamaha recomends a 158 MJ for higher elevations so I will leave it and play with the air screw and the timing pump screw.

I appreciate your guys input on this matter.

On a side note has any one heard that a PRO CIRCUIT T4 runs the bike richer than the stock system? I thought I saw that somewhere on TT?

  • mikeolichney

Posted December 20, 2001 - 07:44 AM


The jetting that we have up here at 5000ft when it is 30F out should be about the same as the sea level guys at 70F. I did the BK mod and am running main jets of:
168 at 30F
165 at 45F
162 at 60F
The reason you need to go richer after the BK mod is that the engine is not getting the extra squirt of fuel at wide open throttle. You need the larger main jet to replace the lost fuel.

Dont take my word for it, try it yourself. You can change a main jet in about two minutes. Find a steep uphill and run the bike WOT with the different MJs. Write the temp and altitude in your manual so you remember which one worked best.


Posted December 21, 2001 - 06:59 AM


Mike, Wow I am surprised at the size's on your MJ at that elevation.

I am a "X" street bike racer and I have jetted a ton of bikes but I have to admitt this is the first bike that I am having this much trouble with.

I am swinging by the dealer to pick up the jets today you recomended. I was also thinking of changing the piolet to a 40 to try and get it a little crisper off the throtle. I have a theroy that if i can get it to run close to lean now with the cold weather then It should be perfect for the summer :) I hope I am right

Thanks for your help.

  • mikeolichney

Posted December 21, 2001 - 07:49 AM


Pokey, I got your email. Can you meet me tomorrow at Berthoud? I don't think your problem is jetting. I have also had the plug fouling problems-do a search under "fouled plug=foul mouth" and you will find a novel. I almost had my bike die while doubling Berthouds long whoop section on the north track. Its a bad problem.

I think I have some things that might help (look at the posts) and we can try them if you can make it.

BTW, how do you respond to an email sent from TT? They always say "do not respond to this email."

  • Rusty

Posted December 25, 2001 - 03:59 PM


If it's sent by IM instant message from TT, you'll have to come onto TT and IM them back. Apparently it doesn't link to the sender's email address.

  • Rich_in_Orlando

Posted December 25, 2001 - 04:23 PM


Here's my 2 cents: When I did the KL mod (BK on a '99 carb), my jetting was right on before I started. I didn't touch the jets after the mod and it runs perfectly, just a little crisper than before and no more bogging. I went from a +4 sec squirt to about a .75 sec squirt. If your bike ran right before the mod, try going back to original jetting and see how it goes. Doing the BK mod should in no way make your bike run richer. (I'm stating the obvious here, but it seems like something else has gone wrong unrelated to the accelerator pump.) If it still runs too rich, maybe you have a clogged air jet or something like that.

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