91 kx 250 stock carb setup.

Hey Anon,
Proper and correct jetting is something that can only be achieved in person by a REAL MECHANIC that KNOWS how to "read" a spark plug,,,With the mods you mentioned.. you need to know the stock jet sizes..a close guess would be reduce the main jet by two or three steps and lower the needle one clip position... oil mix should be at least 32:1....or better yet 28:1.. KEEP the oil mixture and jet the carb for performance....( I see TOO MANY IDIOTS that instead of jetting a carb correctly just reduce the oil ..some as low as 50:1(INSANE) just to keep from fouling plugs.).. then WONDER why their engine doesn't last long... hahaha????
YOU > BE SMART!!

Insert a screw driver to the carb's adjuster screw. Turning clockwise will increase the flow and turning counter clockwise will reduce the flow.

try doing a idle drop procedure. this will help out alot.

take your float out and see if it will float if it sinks replace it also replace the needle set.

Stock Jetting for a 1994YZ250 is:

350 main
45 pilot
J8-6EJ33-61 needle

Adjust your jetting down one size for each 1000' of elevation above sea level. Needle clip position on the needle fine tunes the pilot circuit.

Scott

check and make sure there is no trash in the carb. to do so take off the float bowl which is on the bottom if the carb then see if gas comes out while the float is down, if there is no gas then take off the float (pull out the little pin) then the float needle, then with an air hose blow through the hole that the float needle was in.

You can purchase a manual for about 10 dollars
Email your system/phone model number to sales at aaa-avad.com for further instructions.

Engine Top End:
Auto Decompressor Bolt 104 in·lb
Cylinder Head Cover Bolts 87 in·lb
Cylinder Head Bolts: M10 36 S
M6 104 in·lb S

the S in that means the specified pattern ... just like tightening car tire bolts... please note all that it its INCH lbs....

don't know why it says just 36 for the M10 bolts unless they left out inch lbs

Anything else let me know as i've got a manual for the 250 f... actually i've got a few different ones

Robert

Please take a moment to rate this solution as i've taken a few minutes to find the manual thanks

Does it have a stock pipe,carb,any modifications! If its stock,I would put a new ring and piston in it,it seems like your getting a lot of blowby,also make sure your air filter is clean. It would help if you used an iridium spark plug.