07 WR250F JD Jetting help plz

JD Jetting Kit current configuration...

Altitude: 0 - 1000 feet

Temp: 65F - 90F

Needle: JD Red Needle 4th Clip Position

Main Jet: 185

Leak Jet: 60

Pilot Jet: 42

Other Mods: Grey Wire cut, stock exhaust with performance tip & 3/4" hole drilled in baffle, AIS removed & throttle stop changed to YZ throttle stop.

Current Temperature: 65F

Bike starts and idles nicely bogging a bit in the first 1/4 throttle.. backfires when letting off the throttle and deaccelerating...After warm up fuel screw adjustment wont make bike start to stutter and stall till fuel screw is almost completely closed and seated. Here is what I'm thinking of trying next...

Needle: JD Red on 3rd clip

Main Jet: 175

Pilot Jet: 40

All the rest the same...

Don't have much experience jetting so suggestions are appraicated..

Do the 175 main

Leave the pilot alone, open the fuel screw to 2.5 turns

Move the needle to clip 3

Put in a smaller leak jet (#40)

Do the O-Ring mod

Do each change one at a time. Make the change, ro for a ride and test, adjust further if need be, once it is fine, do the next change.

Thanks for the advice William... I forgot to mention that i have already done the o-ring mod and removed the snorkel and opened airbox cover. I will try the red needle in the 3rd clip and a 175 main but my JD Jetting Kit didn't come with a #40 leak jet.. it came with a #60 leak jet... also I thought that if your fuel screw didn't stall the bike between 2.5 - 1 turns you should change it untill it did... I will try new settings and order a new leak jet if required.. Will post results of new settings...

You have leak jet and pilot jet confused. Pilto jet works in confunction with the fuel screw to set the idle mixture. Leak jet is on of the things you change to adjust the AP circuit to prevent bogs. On an alloy frame bike, I suggest considering a adjustable leak jet as swapping on the alloy framed bikes is a royal PITA.

To set the idle circuit, woram the bike fully. Start to close the fuel screw. The bike should stall when the fuel screw is closed or nearly closed (within 1/2 turn). If the bike does not stall, you need a larger leak jet. Once you know you have the right sized pilot jet, you open to about two turns, start the bike. Start closing the fuel screw till the idle becomes rough, then open till it just smooths out. This is the minimum amount the screw can be open.

The idle circuit also reduces (cannot eliminate) popping and backfires as these occur when the throttle is closed from high rpm.Tweaking the screw between the minimum setting you found above and three turns, you can try to see if further opening reduces the popp

So since my fuel screw doesn't stall the bike untill it is completely closed I should go with a larger pilot jet?

I've moved the red needle to the 3rd clip position and have tried the 175 and 165 main jet.

165 main seems to work the best but its still backfiring when I let off the throttle. I guess thats where the leak jet comes in?

I think I'll order an adjustable leak jet tommorow because like you said it is a pain to get at I want the next time I change it to be the last.

My buddy has the exact same bike ( we bought them together ) he installed the GYTR jetting kit and his will lift the front tire off the ground in 1st & 2nd, mines not there yet..

If the bike will stall with the fuel screw closed, then the pilot is fine.

To reduce the backfiring, open the fuel screw more. But no more than 3 turns. Do you still have the ACV (reduces backfiring) and AIS (can cause additional backfiring) enabled? Main has nothing to do with backfiring, it is only used between 7/8th's and WOT.

Leak jet controls the volume/sensitivity of the ap squirt. This is the source of the bog.

Remember, I said to make one single change at a time and test. If you do multiple things at once, you may not know what change did what and could end up wasting a lot of time.

I have removed the AIS... I dont know what the ACV is William. Could you please explain for me. Thanks again for your help. I've ordered an adjustable leak jet today. Should be here in a few days...

The ACV is the 'coast valve' on the side of the carb. It is used to add a little bit of fuel on decel to reduce popping/backfiring. Some popping is normal. The more open the exhaust, the more pronounced it will be. You can try to open the fuel screw more, no more than three turns, to reduce it further. I do reccoment a second O-Ring on the fuel screw shaft to provide additional friction to help hold the screw in place.

Sounds to me like you have the correct pilot. Bike stalls when the fuel screw is fully or nearly closed.

Did you do the O-Ring mod yet?

O-ring mod is done.... So the ACV is a screw on the side of the carb? Closing it will disable it? or do i want to open it more?

No, the ACV is the little cover on the side of the carb, held on by two screws. Inside that is a diaphragm and a spring. If you do not know what you are doing, I suggest leaving it alone. No, to reduce the pooping further, you can open the fuel screw more but no more than three turns.

Adjustable leak jet arrived today.. will be installing this after noon.. will post results...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By Rixter
      A tiny clear rubber tube on bottom of carb.  On bottom sort of on side, by floats, the other end just hanging down.  Was it always like this? Or does the other end go somewhere?  Today after multiple trys with kick, choke on/off ,,,fuel keeps pouring out the tube.  This bike has always been hard to start.   Thanx  guys!
    • By Doukis1
      New spark plug, new air filter. Went for a ride and all was good. Hadn't run it in a week and a half. Now it won't start. Getting spark. The plug is dry. Is it possible I over oiled the filter and it has somehow gummed up the carb/ float? Thanks
    • By mbennett95
      My 01' yz125 seems to be requiring a large amount of throttle to get off the line. I've ridden plenty of properly jetted 125's and none required quite so much throttle work from a dead stop. Even slipping the clutch it wont get going without a pretty healthy amount of throttle. Thinking it just needs a clutch rebuild kit and maybe a basket. Any info appreciated!
      If it helps any here is what it has done.
      FMF Fatty, VForce 3 reeds, and an iridium plug.
    • By Sam W.
      Hey all, I just bought a street legal 2005 WR250F. Took it out once three weeks ago. Did about 60 miles on the dirt and 15 on the road, bike ran great. I took it out this past Sunday and was about 75 miles into my ride when the battery died. The battery is cheap, but it is brand new and was on a battery maintainer the whole time while it sat in the garage. I kick started it, and it fired right up. I was on the road for about 5-10 miles in fifth gear when I felt the bike slow down a little bit, and I noticed the sound coming from the bike sounded a bit deeper than usual. About a half mile later the bike started to bog down like it was out of gas. I filled the tank back up and experienced the same problem. The bike began to bog down, then puttered out like it was out of gas. Eventually the battery completely died and I was not even able to kick start it. I trailored it home, hooked it up to the maintainer, waited a couple hours, and the bike fired right up with the electric starter and the choke out. However, it was still puttering a lot when it was idling at this time. If anyone knows whats up, I would appreciate any and all help. Thank you. #Yamaha#wr250f 
    • By Ndh87
      I’ve got an old barn find ‘83 CR80R that needs either a new carb or a rebuild kit. I haven’t been able to find either anywhere. 
      Does anyone know where I can find either?
      housing, bowl and all the hard parts seem fine, if I can find a rebuild kit with a new float I think I’ll be ok. Right now it runs but only when I leave the choke on, smokes heavily and likes to bog down on takeoff