Still no luck with BK mod

Okay, I need some more help/advice on jetting my 00 426. I just changed my pilot jet from a 42 to a 40, I have an 01 needle in the 4th clip position, 162 main, 1-1/2 turns out on fuel screw, all other jetting stock. I first tried the 01 needle to solve my bog problem- almost but not quite. So I turned the BK mod in more, added the 40 pilot today- it got worse. Now its closer to when I had all stock jetting with 2-3/4 turns out on the fuel screw. It was only about 52 degrees today, which could have something to do with it.

Could someone explain to me what circuit affects what throttle opening? This might help me better understand how the air and fuel are flowing through the carb and which jet to change to chase down the problem. I can open the throttle wide open from an idle, as long as I don't whack it wide open immediately. If it do it somewhat slowly, I have no bog at all. Any help/info would be appreciated. Thanks again to everyone for all the help in the past.


Simply based on the statement:

So I turned the BK mod in more, added the 40 pilot today- it got worse.

You reduced the duration of the AP and you reduced the pilot size and it got worse. Give it more gas down low instead. First restore the AP by turning out BK mod. Then try the fuel screw (out). Then back to the 42 pilot. Then pull the needle up one more.

The pilot circuit (pilot jet and pilot air jet) and fuel screw are the main circuit in less than 1/4 throttle. The needle is the main circuit from 1/4 to 5/8 throttle. The main jet is the main circuit above that. There are charts showing the overlap at each throttle position. It isn't cut and dried like I just described.

I don't know of a way to get more AP squirt on a '00 426. Anyone?

Good luck,


Good luck,


Hey what's up Cowboy. It sounds like you are having the same problem as I did with my 2000 426. It sounds like your accel. pump timing screw is not adjusted properly. This adjustment is very critical. My bike had stock jetting and it had tons of bog. If you would wack the throttle while coasting around it would let out a loud burp and a blah... It sucked and was very frustrating. So I decided to do the BK Mod. I did the BK Mod and I messed with the pump timing screw and it still had the bog. I was very disappointed until I started messing around with the pump timing screw. I eventually got the pump timing screw dialed in and with jetting advice from Shawn Mc and my bike runs awesome now. I ended up running the pump timing screw at 1.25 turns in from when the screw makes contact with the black pump cam. I went to a 45 pilot with 2 turns out on fuel screw, stock needle position and a 168 main. My bike runs awesome now. I can coast around and straight out whack the throttle and instead of a bog the front end comes up, it is great. The 45 pilot jet seemed to make all of the difference in eliminating that small amount of leftover bog that the BK mod did not take care of. I still feel that I need to tinker with the fuel screw and pump timing a hair more but it is pretty dialed now. Another important thing is to readjust your pump screw (BK screw) after messing with the pump timing screw since it will affect the squirt duration. I hope this helps and good luck...

Alright guys I am going to jump in on this thread too because I am having the same problem. I just did that setup you were talking about on my 01' 426. It has a severe bog now that it never had before so I have resulted in jetting. I tried the 45 pilot, 168 main, and fuel screw about 1.75 turns out. also raised the needle to the fifth position from the top. And I put a new plug in. Now it ran great for about a lap and then it gradually started popping and missing etc. under hard throttle out of turns etc. Now I am pissed I have been all through that carb and cleaned it, tryed a bunch of different jets etc.

So what did I do, I went back to stock 162, 42, needle in the 4th pos., and air screw at 1.5 out. I fooled with the BK screw by turning it out or in. Ques. on the BK mod screw? If you turn it in is that limiting the fuel the AP is spraying or giving it more, maybe I worded that wrong, how is affecting the duration of when the spray happens? I am so tired of messing with this dam bike. I fouled another plug cuz I was stabbing the throttle after a I did a couple of laps and was sitting there in Neutral, BOG BOG BOHG BOG BOG, dAM! I am fed up, Bike is going to sit for a while, needless to say I had to get my bud to go back to the house and bring the toolbox so I could change the plug, to a plug that was partially fouled out from the bigger jets of earlier in the day. I know this is a book that I am typing I am just letting off some frustration? What do you think? I have gotten alot of different opinions, but Cowbona your situation sounds just like mine. Thanks, Frank

I have an 00 426, the bike was completly Stock when I got it except for a White Bros R4 exhaust.

The bike had bog, de-excel poops and was just nasty to ride....

I am now running the following and the bike is a blast to ride.

<ul type="square">[*]BKmod = Done[*]Blue Wire = Done ,No Noticable change[*]Valves = Checked and in spec

Jetting[*]Main = 168[*]Pilot = 45[*]Needle = 1 clip down from stock (Raises needle up one)[*]Air Screw 1 3/4 turns out[*]Accel pump screw standard (Chk Manual)[*]BKmod Adjust .5 Sec Duration[*]All Other Adjustments and Carb Specs are stock

Also note make sure that freaking float is adjusted correctly, Me I adjust it just below spec

Well that works for me, I am not sure what level (Above sea level Hollister CA is at, But I have run this in Clear creek and thats up in the air and the bike performs flawlessly.

I have never fowled (Beerrr-Cakkk, cluk cluk) a plug knock on wood....

I also run 91 Chevron or 76 New GAS evry ride, Except when I eat at the TacoRia then its bad gas and that gets old real quick :D But what can I say I love that place :)

[ May 23, 2002: Message edited by: EgoAhole ]

I guess I should have mentioned, before I put the 40 pilot in- BK was about 5mm of stroke, 01 needle, 42 pilot, 162 main, 1-1/2 turns out on fuel screw. Bike had a small stutter when whacked wide open, slight hesitation when whacked open going down the trail. Now I'm at a 40 pilot with 1mm BK and all other jetting is the same. Now I have a BIG stutter when whacked open from an idle, the bike will sputter and die. I may try going back up to the 42 and trying that. I'm also thinking about picking up a 45 pilot and trying that. Slowly but surely I'll get rid of that bog! :)


I know I have been talking about this same topic for weeks and I have found out one thing, Everyone's bike runs different. LOL I tried that exact jetting yesterday and it didn't perform well at all. You are west coast though and I am east coast. DAm sure wish I could have gotten it to run good with those jets, I am now back to almost stock except for the BK mod which I need to fine tune because when I first did it I had no bog anywhere, now I have the definite bog if you whack the throttle while sitting in neutral. Not much of a noticable bog though going through the track with the stock setup jet wise. I will get it back to normail eventually. LOL Sure does make you madder than hell when you foul a plug in the middle of the track and have two huge hills to get up with a bike that won't start. I almost pushed it over in a mudhole and left it there overnight. Not the bikes fault though it is mine for messing w/ a great running bike to begin with!! LOL Frank

Aggree location/elavation/humidity and temp all play crucial roles. Its simply amazing to me that the YZ is so tempermental in differant geo zones.

I am sure you have done this but I will ask anyway.

Have any of you spoeken to the locals around yer neck o d woods regarding jetting and all?

Best of luck ....

[ May 23, 2002: Message edited by: EgoAhole ]

it's funny I am the only one around here that I ride with anyway that has a 426. Everyone wants one after they rode mine (when it was running great). I wish I had someone close to compare with. I just hope it is jetting and not electrical. But after going back to stock jets yesterday and seeing an improvement even though I still had the bog off idle, I think I can rule out electrical. My mechanic at work is going to do a carb sync on it next week and check the float specs etc. So hopefully I will get it back dialed in the was running before. Thanks, Frank

My '00 426 is jetted the same as EGOs except for stock needle position, no BK mod, has a PRO-CIRCUIT T-4, has never bogged once, and I live in WI.

I think the problem must be from bike to bike as much as climate.

After reading these posts I feel very lucky, my bike starts in 2 kicks always, have never fouled a plug, and doesn't have a bog. I hope I didn't just jinx myself. Mike

there are various differences between this side and the WR side. the first is that you lot have started calling needles the '01 or '02 and i hardly know what's what.

however the reasons that you are having so many troubles are clear to me having been there.

there is a relationship between the PJ and the PAJ. if you lower the PJ without a smaller PAJ you have lots of air but less fuel so you're running leaner.

the APJ needs to be reduced to a spit as it only helps from closed throttle for a fraction before the PC reacts and catches up. i should know; i ran my bike for 9 months without it while i set my carb up.

so the answer was to go from a 100PAJ to a 75PAJ to match that 40PJ you fitted.

these bikes don't bog when the jetting is spot on. they don't bog when they're very rich. but they do bog when they're slightly rich.

if you look at the jetting in my signiture you'll see how much leaner i can run succesfully. this proves how rich YOU are :D:) i'm not lean, i'm spot on.

and i'm not going to say awesome (dam, there i go)

there is a correlation between the PAJ and the PJ and for this go to a major thread on the WR side called "Jetting Q's". just go to WR side and back 45 days to april 20th OK?

i have set up a chart there for PAJ/PJ.

BTW if you do lean off the PJ all you can do is wind out the PS to try and compensate. 2-3 turns are often needed but they're a bodge and the real answer lies in getting the right PJ to PAJ ratio.

all things being equal at small throttle openings the rule is easy

15 of air to a PJ.

the smallest PJ is 35 and the air for it is 45 (my signiture needs modifying).


35 45

38 60

40 75

42 90

45 100

48 110-125

if you're down on the PJ making it weaker/leaner = out on the PS to compensate.

too low a PAJ= PS in to 1/2-1 turns.

ratio right? =1.5 turns.

this all relies on you turning the APJ right down to a spit of fuel.

also that you realise that this is for 1/8th throttle or low revs in second (not idle but low ok?).

plug fouling is only about 20-30% to do with your PC. it's 70% to do with your needle straight. so if you're flooding when starting look at your needle straight. for instance a rider at altitude with a P needle and a huge 45 or 48 PJ whether balanced to the correct PAJ or not is chucking in so much fuel on top of that P needle that the thing simply can't cope when starting can it? 30% on top is for the STANDARD jet that it may need. so a 48!- jesus gimme a break.

hick has changed the figures that got me to here. he lives at 10,000ft so it's hard to be perfect BUT IT IS BALLPARK for altitude. for everyone else below 3,000ft this will be spot on.

it appears that higher altitude needs a wider needle. so an M at sea level becomes a an N and then a P and then an R. i don't believe that an R is needed and nobody has tested the way i need it sorted to verify if i'm wrong. i'd be glad to be wrong so that we could build a graph of figures up.

these leaner needle straights (P and R?)at altitude may rob a tiny fuel as you move off. you'll only notice it over like 2 yards in first-no clutch. if you have to go over the natural revs to get going and feed a bit of clutch you've got too wide a needle.

here in the UK at sea level a P needle creates a bog. but hick says at altitude anything thinner than a P means he's liable to foul a plug!!

in a nutshell get those ratios right.


Originally posted by FASTFRANK:

My mechanic at work is going to do a carb sync on it next week and check the float specs etc. Thanks, Frank

Not to be a smart a$$ but... You can't synchronize your carbs when you only have one carb. :)

Good luck sorting it out.

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