Eliminating bog

Has anyone completly eliminated bog when you snap the throttle open (0 to 1/2 or 3/4 throttle)?

If so, post your jetting setup and altitude.

My bike runs perfectly except for the bog when I snap open the throttle to around the 1/2 throttle range. It doesn't happen when I open the throttle a little slower. I'm thinking of going to the E series needle (ERS, EKP) to help eliminate the bog.


I have eliminated it to the point where I am happy with it.........but.......different strokes in this case.

I have the feeling some of you folks are pulling a hell of a lot more out of your ride than I am.

If your in the area, It may be easier to ride mine for comparison and see if the set up is what you are looking for.

Just a suggestion.


Mine got WAY better once I went to YZ jetting and timing. I think the jetting was the biggest help. Based upon a recomendation by Hick, I purchased the EKQ needle, and changed my pilot from a 42, to a 38. Only issue I have right now, is if I'm really giving it hell above 12K, I can still load up a plug. However, I still haven't got the BK done yet, maybe this week since my rear tire is laid up.........

Dodger :D:)

Both of my bikes run perfectly with absolutely zero bog when snapping that throttle....pump squirt adjusted to .5 sec

Bonzai :)


At Rampart (7000 - 9500ft):

38PJ/65PAJ/EKP#3/150MJ/160MAJ/1.5 turns pilot screw.

Runs awesome! No bog whatsoever to wheelie anything.

Higher elevations (9500 - 13K):

38PJ/65PAJ/EKQ#2.5 or EJQ#2/145MJ/160MAJ/1 turn pilot screw.

Ran great at Crested Butte...except too rich from 1/2 - FT when running with a 150MJ instead. Thus the change to a 145MJ. Havent run this setup yet, but expect it to be nothing short of awesome!

Remember that I have completed the BK mod, have WR timing, and have the stock, uncorked exhaust.

Good luck!


Where did you get the EKP and EKQ needles? I'm going to stop by Excel Yamaha today to see if they have them. It seems like the bog is from a too rich situation. Isn't the EKP needle richer than the stock DRR? I was thinking of going to something like a ERS if there is such a needle, basically changing the taper and going a touch leaner.


How did you adjust the pump squirt on your '99 WR?

[ September 25, 2002, 02:44 PM: Message edited by: Chaindrive ]

Hey Yamakaze,

Why the different jetting on the bikes? I know the WR and YZ differences, but aren't you using YZ timing in the WR? Just 'curosity' :)


First of all, the part #'s for those needles...

EKP - 5JG-14916-EP

EKQ - 5JG-14916-E1.

Both I believe are listed under either a '99 or '01 YZ426.

Second, the DRR needle has a larger straight diameter than the EKP and EKQ needles (R vs. P and Q), the needle taper of the DRR needle starts roughly at the same position as the EKP and EKQ needles, and the DRR needle has a smaller taper angle (0.75 degrees) vs. the EKP and EKQ needles (1 degree). What does all this mean? Well, on your pilot circuit, we'll be richening it up slightly (P or Q vs. R), and you'll be getting more gas throughout the midrange and upper end by allowing more gas up the carb slide by using the E series needle (more of a taper angle). Dont forget, that you'll be decreasing your pilot air jet and main air jet as well.

Overall, folks have found that the 38PJ works well in conjunction with a 65PAJ. You're using it with a 75PAJ and a thicker DRR needle...thus, pretty lean on the low end.

You can get the pilot air screw and spring combo from Sudco for about $15...as well as the 160MAJ. It'll save you from buying lots of different pilot air jets...

Hope this helps! Call me if you have any questions...


I have recently put an EKP, the local mechanic told/ordered me a 100PAJ because that is supposedly that comes with YZ's. So, Larry I am still new to jetting, but aren’t the E needles richer, and you increase the PAJ to help lean things back out, I guess I don't understand why the 65PAJ in your response to wicked. A little carination, please.

Just when I think I am starting to figure this out :D hits again. Thanks :)


The reason I'm/Wicked will be using a 65PAJ is because of the use of the smaller PJ (pilot jet)...a 38 in this case. He's definitely a bit lean on his pilot circuit (the 38PJ together with a 75PAJ and an "R" diameter needle).

I've never heard of anyone using a 100PAJ with any series of needle jet/pilot jet...that sounds incredibly lean to me. From what I've experienced/learned, using a 42PJ one should go with a 75 or 85 PAJ...

If you really want to learn more, you can order the James Dean jetting guide from the TT store. It'll show you affects throughout the throttle range of changing a component of jetting (for eg. the difference in a 38PJ vs. a 42PJ while using the same needle and main jet).


Larry thanks for the info. I was curious about the 100PAJ, I had a 75 in to begin with, and I am just going off of the mechanic's advice. With the 100 the bike feels allot crisper/quicker, could this be because I might be to lean? I have no hesitation with throttle, just a little bubble at 3/5 throttle, or 60-63 mph. No backfiring during deceleration. Do you think I should go back to the 75, so I don't mess up the engine?

I will take a look at JD book. Thanks allot I really appreciate the help. :)


About how many turns out on the pilot air screw would equal a 65 PAJ? I ordered the needles, not soon enough for a test this weekend though.

Roughly 1/2 a turn or a fraction more out from lightly seated. 1 turn is approx. equal to #100 PAJ.


Just as an update, I switched to the EKQ needle and there is virtually no bog. The E need made a huge difference in power delivery. I haven't gotten the pilot air screw yet, but for now I'm happy with the new setup.


The 42 pilot may be a tweener, stock YZ jetting is 42 pilot and 100 PAJ, so your mechanic is not a total idiot.

The PAJ works in conjunction w/ pilot size, and changes in the PAJ are more pronounced at higher rpm. So once you find the best pilot, just guessing at the appropriate PAJ, you can fine tune for the latter.

I just go bigger until it gets too lean. This is easily noticed via the following symptoms:

Surging during freeway cruising. I don't ride mine on the ten, but if I did I'd be fifth gear and about 50 to 60 mph or a relatively high rpm but low throttle. That is the PAJ circuit, and if it surges here it is too lean.

Too much popping on decel. During your "freeway" run, chop the throttle off abruptly. One or two small pops is okay, but if you get one loud one or several louder pops you are too lean on the PAJ and need to go a bit smaller.

Hope this helps.

Thanks Hick, I messed with the paj the other day the bike runs good with a 75 or the 100,a little leaner with the 100 but not much popping when chopping the throttle compared to the 75. I am going to try a different diaphragm with both paj's and see what happens. :)

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