rich running yz250

[biged]

i own a 1998 yz 250 that always runs rich. i have put rad reeds in it. a fresh top end and leaned the pilot out to a 40 and still will foul plugs and runs sluggish on the bottom end...

 

[Mophuka]

I had the same problem. I ended up having to change the needle, main, and pilot. basically redid the whole thing from scratch.. went with a smaller pilot and main. can't remember what they are off hand. but being that the needle is different my jetting probably wont work for you.

 

[j32]

you should follow the directions on the reed package,it should tell you that if you do not use the factory reed stops ,you should lean the main jet 1-2 sizes at a time
simple mistake,and if you have black drool,thats oil not burning completly-try klotz ,it burns cleaner than a lot of oils out there,repack the silencer-its probably full of the gooy oil as well
check the crank oil and see if it is burning it
put the stock pilot back in,check the plug after changing oils--keep us posted

 

[biged]

you should follow the directions on the reed package,it should tell you that if you do not use the factory reed stops ,you should lean the main jet 1-2 sizes at a time
simple mistake,and if you have black drool,thats oil not burning completly-try klotz ,it burns cleaner than a lot of oils out there,repack the silencer-its probably full of the gooy oil as well
check the crank oil and see if it is burning it
put the stock pilot back in,check the plug after changing oils--keep us posted

i currently have switched off the yamalube after putting in new top end. i am using belray synthetic @ 50:1 and no change. i am currently running the main at 162 and boyensen recommends it be at 165. they also recommend i leave the pilot at the stock that is 48 and i am running a 40. still runs real rich and i have the clip at 3.

 

[biged]

I had the same problem. I ended up having to change the needle, main, and pilot. basically redid the whole thing from scratch.. went with a smaller pilot and main. can't remember what they are off hand. but being that the needle is different my jetting probably wont work for you.

i have the main at 162 the clip at 3 and the pilot at 40. that is way lean from the stock 172 main and 48 pilot.still runs very rich....

 

[Mophuka]

I think I have a 38 pilot and adjusted the air/fuel screw. plus the needle is fatter than stock.. also have the clip on the third position.. bike runs alot better..

 

[Rcannon]

I had the same difficulty trying to jet my 97 yz 250 with a rad valve. It was always rich. Jetting returned to stock after I put the yamaha reeds back in.

I did'nt get the bike to run perfect until I milled the head.

 

[j32]

well check the crank case oil and see if it is burning it as well as the premix oil
it might have a bad crank case oil seal, right side,or center case seal ,im not sure if that model used a center gasket or yamabond- i hate that stuff,
change the silencer packing ,it is probably soaked with oil if it is as bad as you say