YZ 250F jetting / revisted

[MXP1MP]

I need some help in figuring out where to head in jetting on this bike. Due to recent weather changes the bike seems suddenly lean. The tip of my muffler went from alittle dark like it was alittle too rich and now its gotten alittle bit of whiteness to it. It really hesitates off the bottom, when rolling on the throttle real slowly it doesn't but say you crack it like you would normally and it gags like bogs almost to the bike sometimes it seems like its gonna stall. Then cleans out and rev's freely the rest of the time unless I chop the throttle fully and try it again. The other thing it does is when I chop the throttle it pops some when it idles down.

I'm thinking it is cause its alittle lean cause when its dead cold now its become such a pain to start. Once I get the first warm up the day it usually starts 1-2 kicks. It currently has #40 pilot and the needle is #4 clip and the main is a 178. I have tried turning up the idle but that didn't do anything. I was going to lower the needle to clip #5 or would I be better off just going up on the pilot one or would going up on the main one to #180 work? I know jetting is all trail and error but I just need some input on the direction I should go since my 4 stroke jetting experience is very limited. I'd like to get it dailed in better before the race this weekend. Last weekend a rider went down in front of me and I stalled the bike going from 3rd to dead last. I couldn't get the bike restarted and I didn't lay it over. I was two laps down before I finally got it restarted and I think its become harder to start cause jetting is now off. The temps are in the upper 30's to 50's and I'm running trick 110.

 

[Joe P. 81]

Have you tried adjusting your fuel screw? You might be able to get rid of the bog with this, if not, I would go with a richer pilot. Remeber, when you turn the fuel screw out it makes it richer. If you end up past about 2 3/4 turns out and it still bogs you will probably have to go one step richer on the pilot. If this doesn't help I would try moving the clip to the #5 position. I don't think you should worry about the main right now. It sounds to me like your problems are only in the bottom to low-mid. I'm still having problems with mine as well so don't feel like your the only one. I will be spending all day tomorrow trying to get it dialed in. I'll let you know if I find a setup worth trying.

Joe

 

[MXP1MP]

I haven't tried the fuel screw just tried turning up the idle, I just lowered the needle one clip from #4 to #5 gonna try it out this weekend. I just don't like trying things out during a race day. Hey is that your RM on waunch's site? he helped sell my yz 125 for me, I sold it for 3300.

 

[Joe P. 81]

Yeah, that's my RM. I ended up trading it in when my 250F got here. Let me know if the needle adjustment helped. I've been playing with my jetting this weekend, but I'm still having a hard time finding the perfect setup. My bike was rich when I first got it so I leaned it out. Now it's running lean and popping like yours. The 03's must be more sensitive to the weather or something. Good luck at the AX.

Joe

 

[MXP1MP]

Well changing the needle helped quite a bit, the bike got back some of its snap and its not popping near as much now and it was easier to start. I'm gonna still up the pilot though, I'm gonna try out a #42 I bet that will help with the starting issue's. oh ya btw I was able to ride the entire salem ax track in 2nd gear!! I'm really starting to love pitching this bike over in corners it just rails'em!

 

[tmoney]

Just took my 03 out for the 10 min breakin ride. Starts fine. Idles fine but started hesitating and then popping when idling back down. Its about 40F here in Cincinatti. Anyone have any suggestions. I have trouble deciphering if a 4 stroke is running lean or rich. this is my first 4-stroke. Might this go away with a longer breakin? (ie. should the header pipe glow red?)

Thanks.

 

[tmoney]

Here's a better explanation of how its running...second break in ride....bike accelerates fine and has good top end. At 1/4-3/8 steady throtte in 2nd/3rd gear the bike "sputters". Quick throttle response from 0-1/4 also causes a hesitation about 50% of the time. Pilot air screw is out 2 1/4 turns. Stock pilot=40 and main=178 and stock needle position=4. Its about 40F here tonight. Any help out there? Thanks.

 

[Joe P. 81]

If your bike is popping that is a lean condition. I would try turning out the fuel screw about a 1/2 turn and dropping the clip on the needle one position. I've also heard that a 180 main makes the 03 feel a little stronger up top, but I haven't tried it. I think the weather is what's messing with everyones jetting right now.

MXP1MP- I was watching an old SX the other day and I remember them saying that Ryan Clark's shifter on his 250F got bent or something so it was stuck in 2nd gear, but he said it was perfect because that's all he needed. It's amazing how far these things rev. I will try your jetting and see how it works for me.

Joe

 

[tmoney]

Thanks, I will try raising the needle. I left my manual at work. Can anyone give a quick 5 step drill for how to remove the needle the easiest way...i not an amature with the wrench, just never worked on this bike before and I know nothing about the carb.

Also, will raising the needle help with throttle response. It dies when i give it quick throttle, even after warm up. I was reading about the "leak" jet in the manual, seems like that would have the biggest impact on throttle response.

Thanks.

 

[Joe P. 81]

Well, this is how I take out the needle. There might be an easier way, but oh well. 1. Pull the tank, just leave the rad shrouds on and remove the bolts that go into the radiator, it will all slide right off. 2. Remove the two 3mm allen head screws on top of the carb. 3. Using a 5mm allen (I think, might be a 6) remove the gold bolt in the middle of the slide. 4. Pull the needle out with some needle nose or anything else that will fit into the recess. 5. Change the clip position and put her back together. As for the bog on the bottom end, if you can't get it cleaned up with the fuel screw then you might try a richer pilot.

Joe

 

[tmoney]

Thanks alot Joe.