Can't Fix the bog !!!!!!!

Hey Fellas,

I really need your help !

While out practicing last night, and working on my seat bouncing skillz, I was at the bottom of a jump face right out of a corner and gave my 00 426F a quick blip to launch the gap.

Well "Old Blue" decided to choke on the mixture and Booooooogggggg !

Going from a steady throttle to almost stalling on the jumpface, the bike nose dived into the second hump of the double, sending me wailing over the bars. I tweaked my knee and have some sore ribs, but I should be OK for this weekends MX Racing.

Problem is I have no confidence in the bike now when it comes to spots where i need a quick blip.

I had purchased the Factory R&D p-38 and went to a 165 main and 45 pilot with the screw 2 turns out. I am at sea level and the temp is about 18 - 25 deg Celcius.

Any one had the same prob.

I really need your help guys, My confidence in the bike has been lost ! :)


Hold it Wide...

The old ongoing topic. Check the archives, this one has endless topics, even some fix from Tim Ferry's mechanic "BK". Does anyone know if this ever really worked?

I did the BK mod and it does make things better. Still a very slight bog at real low rpm's, but the bike recovers and does not die. This mod also makes the bike more responsive.

I remember Hick or James Dean mentioning that changing to a 01 needle(EJP) also helps.

I currently have one on order so I don't have any results to report yet. If you're interested, the PN# is 5jg-14916-jl-00.

Hope this helps.


00 YZ426F

01 TT-R125L (my son's)

91 CR125

83 YZ490

74 Hodaka Super Combat(gone but not forgotten!)

I also did the BK mod and concur with Mr. MXer's comments. I no longer notice the stumble unless I'm idling in neutral and whack the throttle as hard as I can--stumble while riding is no longer a problem.

As an added benefit the bike is easier to start after a fall, as the reduced accel pump stroke reduces flooding. Good luck

The stumble on my '00 was not as severe as least not from your description. It took some time, but I finally got it spot on. In my opinion, VP C-12 fuel and careful jetting was the best thing I could have done. I think the P-38 simply helped dial in the rest. C-12 causes the stock jetting to be on the rich side, so countering with a leaner main jet gave me very crisp throttle response with NO hesitation or stumble anywhere. I run a #160 at temperatures below about 50 degrees F...and a #150 at anything hotter than that. It didn't require a change in the pilot or needle, just a slight tweaking of the fuel screw according to the ambient temperature. What worked for me may not necessarily work for anyone else.

do you think the bog is from a rich or a lean situation.

too much air or too much gas

hmmmmmmmmmm !


Hold it Wide...


I would be inclined to look at jetting as a possible cause.

Definately check the pump action by removing the seat/subframe. You can see the spray easily and that may be an issue.

Sunday, A friend had a similar problem with his 01 426. When at idle blipping the throttle resulted in a bog/hesitation. He had changed pipes and not jetting. We turned the fuel screw out about 1/4 turn at a time until it was completely gone took about 1 full turn, I dont know where it was when we started though. He should probobly increase his pilot jet by one size and set the screw closer to 1.5-2.0 turns out.

Incorrect jetting can easily make your bike run the way you describe.

Have you changed anything even fuel that may have caused it? Fuel can go bad in the summer. Maybe check for gunk in your carb/jets too.

Good luck

Dave S

HELLO... did anyone even read my reply or are they just not showing up. Someone correct me if I'm wrong, but from what I understand the 01 426 does not have the stumble off idle or no where near as bad as the 00. I believe this was accomplished by modifying the pump (same effect as the BK mod) and changed the needle. I don't think any other changes were made. At least I can't discern any other part # changes between the two models. So, wouldn't it make sense to go to the 01 needle and modify the pump either with the p-38 or the BK mod? They both accomplish the same thing although I believe the BK mod is much more precise.


00 YZ426F

01 TT-R125L (my son's)

91 CR125

83 YZ490

74 Hodaka Super Combat(gone but not forgotten!)


The '01 EJP needle is richer on both the needle straight diameter and clip. What clip position are you using? You may simply need to move the clip 1 step richer, especially with the p-38. Did you clean the top of the accelerator pump diaphram? Crud often builds up on top of it.

[This message has been edited by James Dean (edited 06-07-2001).]

Ooops! I meant a #158 main jet....not #150.

Dirtdad: I read your reply...twice. I simply had nothing helpful to add to it... :)

[This message has been edited by Boit (edited 06-07-2001).]

The BK mod sounds great, but I'm a newbie to the four stroke and FCR carb world.

I dont think i'm ready to tackle the Drilling and tapping, and timing the spray for .3 of a second.

What about jetting and fuel screw ?

anyone else using the p-38?


Hold it Wide...

I really appreciate you input and advice fellas.

So to sum things up, after work today I'm gonna remove the carb and clean it, order a 2001 needle, but in the mean time go one step richer (move the clip down one), reinstall the carb and before attaching the subframe i'll check the accel pump spray.

WHat should I be looking for ?

What are you guys using for main and pilots ?

any one else out there with the p-38, what are u using for main, pilot and how many turns out on the screw

Thx for your input

guys, I wasn't feeling sorry for myself or tooting my own horn. Maybe I worded it wrong, but my initial reply was just as much a question as a suggestion! I guess if professor Dean didn't correct me (I think) then it must have been valid info.

Oh and James, I meant the professor Dean thing purely as a compliment.


00 YZ426F

01 TT-R125L (my son's)

91 CR125

83 YZ490

74 Hodaka Super Combat(gone but not forgotten!)

[This message has been edited by dirtdad (edited 06-08-2001).]

I'm still running the stock needle position JD. but I plan on moving it down one tonight after work.

got any jetting Ideas ?

I have the stock exhaust and a Big Gun oversized Race Series.

I bogs bad with both pipes.

Gotta be a jetting thing !

Thx Fellas


Hold it Wide...

dirtdad, thanks for the compliment. Yes you were accurate in the jetting changes.

Smitty, keep the other settings the same. They look close to what I would suggest. Try the pilot screw in and out (1 1/2 - 2 1/4 turns) looking for best response.

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