Jump to content

2002 Yz250f Jetting advice (blacking plugs fast) (JD carb kit)

Recommended Posts

Hey guys I need some jetting advice. I have a 2002 Yz250f and have been messing with the jetting and right now i have it so far off it wont kickstart. At this point in time I have a jd carb kit installed with using the blue needle at the 5th position (second from top), 185 main jet, 42 pilot jet (40 pilot is stock on a 2002 all other years are 42 pilot stock.) since the jd carb kit said use stock pilot I put in a 42 pilot jet thinking that was the size it was referring to since it doesnt say an exact number on the JD carb kit instructions. R&D adjustable fuel screw set at 2 1/2 turns out right now. Recently added FMF powercore header and a boysen quick start 3 adjustable leak jet with hot start lever on handle bars. I added all of these mods at once and would really like some advice on where to go from here because as of right now the bike will not crank at all and if i roll start it the plug comes out wet black fouled(too rich?). Also Im going to do the BK mod later today to keep my accelerator pump to a much shorter duration. At this point in time it sprays for over 4 seconds with a really strong shot. I have the quickshot 3 adjustable accelerator pump set to 1/2 turn out which the paper work said is equal to a 35 leak jet. Remember this though, I added all these parts over the winter and do not have a good starting place for jetting because I know it is way off than before. Somtimes the bike will kickstart first time, other times it wont crank no matter what I do and the plug comes out completely black. I know the jetting is my problem because I just put a brand new wiseco cam chain and tensioner on it this week. It started first thing yesterday morning then i pushed the choke in after letting it run on choke for about 10 seconds then died and has not started since. Put in a new a plug and now it will not fire at all.

 

current information on my 2002 Yz250f (as much as i can give you for an idea) (also not running / kick starting at this setting and blacking plugs fast)

Elevation 900-2000 ft

Temp 50-100 degrees F

Sprark Plug - CR8EIX (advice on plugs also?)

Nonethanol 93 pump gas

RD adjustable Fuel Screw 2 1/2 turns out

Pilot Jet 42 (Recently changed from my 40 pilot to try it and i  dont think its right either)

main jet 185 (162 stock) -as per JD carb kit instructions

Needle - JD blue needle clip 5 (2 from top) ;(also willing to try the stock needle just need advice)

Starter jet - 72 (stock?)

 

Found this on another thread it shows a magazines recommendation on jetting and the stock jetting is in parenthesis if changed.

2002 YAMAHA YZ250F JETTING

Main: 178 (162 stock)

Pilot: 40

Needle: OBEKP

Clip position: 4th from top (4th stock)

Fuel screw: 2 turns (1-5/8 stock)

Leak jet: 90 (100 stock)

 

Seems to me like it is just getting way too much fuel when I follow the instructions for my elevation by JD carb kit. Might go back to exact stock jetting and do the BK mod and try to make my accelerator pump squirt for under 1 second because right now its 4+ seconds. That may be my only problem I am just looking for any advice at all because I have tried a lot now and it is still not right. Pulled it behind a fourwheeler a while and it would not even pull start until I had the fuel screw 2 1/2 turns out or more at 1000' elevation 75F temp.

Share this post


Link to post
Share on other sites

Get rid of the adjustable leek jet!!!!   Go completely back to stock settings.  Just because you have a pipe doesn't always mean you have to richen your jetting. 

  • Like 1

Share this post


Link to post
Share on other sites

Ok I will try installing my old leak jet in the carb bowl and using a size 100 leak jet? wouldnt the BK mod do the same thing by blocking the pump actuator arm from spraying as long?

Also I am looking for somebody to confirm what the stock jetting is because I bought the bike and all the jets had been changed already. He thought the bike was a 2005 when he sold it me lol...

so, try this then?

MJ 162

Pilot 40 stock (or 42?)

stock needle clip 4th from top

100 leak jet

fuel screw 1 5/8

can anyone confirm this is stock jetting for a 2002 yz250f please

 

Share this post


Link to post
Share on other sites

Go to procircuits website.  Go to jetting specs, the box in left, bottom of page.  They have stock jetting and procircuits corrected jetting.    I didn't see specs for a 2002 but there was for 2003 and up.   

  • Like 1

Share this post


Link to post
Share on other sites

The AP mod takes the delay away and makes the spring and arm as one for a more quick and precise squirt

  • Like 1

Share this post


Link to post
Share on other sites

ok thank you for answering so quickly! I have done the bk mod on my friend FCR carburetor before and we got it to spray under a half second, i think that is what causing my black plug, way too much fuel from AP? starts first kick idles good wont crank at all after you turn it off

Edited by dimebag828

Share this post


Link to post
Share on other sites

stock is 178 38 4th clip 1.75 turns

PC is 178 38 4th clip 1.25 turns

2003 yz250f which should be same as 2002

Stock leek is 105

Share this post


Link to post
Share on other sites

You want to time the squirt to where it just misses the slide

the leek jet controls how much fuel is in that squirt

leek jet is the slight twist of throttle.    Usually you get a quick bog right at first twist

Share this post


Link to post
Share on other sites

ok thanks, i will work on the accelerator pump actuator arm when i take the carb off soon.  here is the jetting numbers i was going by stock, they look different than what PC said.

 

Share this post


Link to post
Share on other sites

where is the best place to buy a large range of jets? I am going to buy multiple jets ranging from 160+. A 38 42 45 pilot and some starter jets too? is motosport the best place to buy different size jets

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Reply with:


×