Yz250f bogging through bowl turns. Carb help!

[Twistedhawke]

Hey guys! I was riding at the local track, Joliet Mx, and There are some pretty nice sized triples and a huge tabletop infront of these stands. Perfect place to really air it out. I have been noticing that my yz250f has been slow to pick up speed through the turns before the jump and its really scary. I am in third gear, and if i pinned it in second..I think it'd lose control or not have enough. Idk if im just going too slow for the carb to ever possibly not let the bike bog, or if i should pin it in second. I dont have much time to pick up speed really. Carbs are still sort of a mystery to me. I can tell you that the spark plug is black and sooty. the bike usualy needs the hotstart when trying to start hot, and it just bogs when the throttle is snapped on when in a higher gear. I have to really feather that clutch to pull it out of the bog. Can anyone give me some ideas to try? I live in chicago, so elevation isnt too drastic. Thanks guys!

 

[rmc_olderthandirt]

The first step should be to get your jetting correct. That will make an improvement in everything.

If you are still in a situation where the RPM in third gear is too low and and too high in second gear, then change your gearing.

If you go a tooth or two larger on the rear sprocket it will increase the RPMs for a given speed in a given gear. That would allow you to use third gear instead of second.

Alternatively, you can go a tooth or two smaller on the rear sprocket. Now 2nd gear won't be rev'ed out at that speed.

Keep in mind that it will impact all the turns / jumps so you may make an improvement for one section of track but it could hurt you on a different section

Rod

 

[Twistedhawke]

I never thought of changing the sprocket sizes... how much would i notice if i moved just one tooth up in a size

 

[mideastrider]

I'd start with that "black and sooty" plug problem first. As stated above get your jetting correct. No 250F should have plug that looks like that.

 

[whenfoxforks-ruled]

Jetting or valves.

 

[whenfoxforks-ruled]

Twistedhawke, do you ever ride at a track in Hobart, In.?

 

[Twistedhawke]

No, I've never ridden at a track in Hobart, why did you see my twin or something lol

 

[whenfoxforks-ruled]

There are lots of old YZ250f's popping around!

 

[Matt90GT]

measure your valve clearance and shim properly. #1

#2 - jet the carb. Get an extended fuel screw so you can adjust it easily. Run a #40 leak jet, 45 pilot, stock main, and 06 needle 4th clip or get a JD jet kit run the blue needle.

That will get you up and running great. I have had a few yz250fs and jetted about a dozen others like that. Rip, no lean pop, no hesitation or bog.

 

[Twistedhawke]

The leak jet was the problem ! I swapped the 40 in there and it's running superb now! Thank you guys!! Thank you!!!