250-500cc WR300 sputtering after a fast wide open run...

Just wondering what could cause the 300 to sputter occasionally after blasting wide open for 5 seconds or more ? Could the bowl be runing empty?

Overall she runs great now with the 170 main jet and 40:1 mix.
General riding is proving hard to keep the front end on the ground even when running 14/45 gearing. Next week I will go to 15/45 + the race head

At no point does the 300 feel like its under powered now. My mate (on his husky 510) and I did a rolling start at about 40klm hr to full throttle yesterday and the 300 stayed head to head all the way

Loving this bike

Change the plug and try a 165 MJ
Worked for me

Put a fresh plug in it....do a warm up by shifting through gears no more than half throttle to warm it up then build you speed up to hit 4th gear WOT, pull the clutch and hit the kill switch...otherwise known as a plug chop

If the bowl ran empty the bike will noticeably over rev at some point.

What was your throttle position when it started to splutter...3/4, 1/2 or 3/8?

To me it sounds like the the combo of needle height and pilot jet...maybe even the type of needle.

Do a plug chop.

Yes, what throttle opening does the sputter happen at? It might well be a bit rich at that point. The 5+ second blast heats things up and will bring out any marginally rich spot in the carburetion.

Cool picture , BTW. Looks like you're having fun!

Better watch you don't dig up an oil well

Cheers . It doesn't appear to happen on short bursts, only after a longer wide open runs. When i let the throttle off from a fast run and then try and cruise at a slower speed it runs a bit rough from idle up. Give it 10seconds or so and it's ok again.

sounds too rich, mine did the same

My '09 did the same thing. Lower the needle one clip and see if it helps. That's all I did and mine quit.

+1 on lowering the needle 1 slot.

Only thing my bike does after a WO run is catch the silencer packing on fire