1/2-3/4 throttle bog (WR426) tried but can't pinpoint

Ive heard folks say that bogging between 1/2 and 3/4 throttle can mean Rich or Lean. Help me understand what I have going on.

Bike Summary:

02 WR426

Stock pipe with Pro Moto baffle

YZ Timed & 03' 450 Cam

Stock Jetting

AP squirt: 1sec

Float: 8mm

Temps: 65-80F

Elevation: 800'

Air box lid removed

Air Screw: 2 turns

Performance Summary:

Starts and idles good. Good/smooth throttle response when cracking open from a stop.

Once I get past 1/2 throttle engine bogs down until I throttle back.

So far Ive tried a 170main and the stock 165 main. Needle clip is on #4 (middle). Im off to try the #5 clip position in an attempt to lean it but wanted to confer with the experienced on this before banging my head further.

try a 162 jet

clean the carb yet? Float level?

Cleaned and set!

I went back and re-checked my AP squirt and its more like 1.5 seconds (which is on the rich side). But Im not experiencing any bog off idle or when I snap it from 1/4 throttle. So, I dont think I'll play with that just yet. What Im thinking is that I may try out a YZ needle which is supposed to be more rich across the circuit.

Im choosing the YZ needle route since up'ing the main to a 170 didnt change the response a bit.

Sounds like you're on the right track. I'd play with the needle (both richer and leaner) and see how it reacts.

I'd limit the squirt to around 1/3 second. 1.5 is way too long.

I think that's a bit to long as well but Im getting no off idle bog that results from the AP loading up the carb. In fact my throttle is super crisp in the 0-1/2 throttle range which is why Im electing at this point not to change it until Ive solved mid-to-top end bog.

James suggested an even larger main (175) which I'll give a try today and then go through the needle settings. I'll report back this afternoon.

I had a similar problem with my 02 YZ426. I tried everything. It ended up being crap blocking fuel off inside the tank by the fuel switch. It sounds retarded, but it took me a month to figure that out and it worked perfect ever since!

So far Ive tried a 170main and the stock 165 main. Needle clip is on #4 (middle). Im off to try the #5 clip position in an attempt to lean it but wanted to confer with the experienced on this before banging my head further.

#5 clip is richer (raises needle)..... which is what you want to do!!!!

lean will bog, rich will sputter.

count your clips down from the top of the needle, holding it how it sits in the carb, grooves on top and point below.

Matty, I was using the manuals nomenclature which is reversed. I like typical method of numbering myself. In any case, I tried both raising and lowering the needle with little or not change.

I also tried a 175 mj and varied the clip from 3 to 7 and it only got worse by clip 6........when I engaged the choke while clip was at 6 the bike wanted to die. So, I guess I need to hear the difference between a 'bog' and a 'sputter' because I think I just reached the upper end of the rich regime.

My plan now is to:

a)Return to stock jetting

:applause: Get a YZ426 needle (which is the best?....OBEJP, OCEMP, OCEMN???)

c)Shorten the AP squirt from 1sec to 0.5 sec

d)Start from square 1 and re-test all the jet variations.

Since Im having to start at the beginning I went ahead and made up a Jamesnow to get back some of the low end that was lost with the 450 cam. I'll also check out Mike's lead on the fuel petcock.....never know.

What do you guys think?

OCEMP needle ordered.


Ran stock jetting. I have a bit more throttle before bog (starts at 3/4) but when I decelerate Im getting a lot of drag (feels like its running out of fuel/ wants to die but its not). Having to blip to keep going. Also a bit of popping (not crackling) sounds like wood sticks (not your typical lean crackle) out of the pipe on decel.

Burned suggest I double check the yz timing so I'll check that tonight. Other than that Im waiting on my yz needle and will go from there. Still think I should be able to get my top end tuned somewhat with the mains Im playing with.Dunno

Just popped the cover to find that the dealer didnt yz time the bike when they installed the 450 cam. Fleeced by another dealer. Im off to advance cam 1 tooth.

Which cam, YZ or WR? If it's a YZ450 cam, it won't look like it was "YZ-timed" because the gear is pressed on in a different orientation...it's already set-up, all you do is line up the timing marks. WR400-426 owners used the WR cam and changed it's timing.

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