I have a 2003 sx 250 KTM After rebuild every 10

air filter dirty can cause it to run rich. Should be cleaned every 10 hours of riding.
Mix should be at 40:1 in winter and 36:1 in summer. Use a ratio right dont guess on the mix.

Finally - get a JD jetting kit and install it! Crucial for all ktm bikes.

Curious what jetting are you currently running>

line the TDC mark on the flywheel/crankcasing up , then the cam shaft marks paralell to the cylinder head mating surface then fit chain, fit chain tensioner, take plug out and turn by hand to make sure valves aren't knocking, **** squeeze bang blow! intake fuel, compression, ignition exhaust out

HI. REMOVE THE POWERVALVE COVER ON THE SIDE OF THE CYLINDER.
MAKE SURE THE ARM IS CLIPPED ON TO THE POWER VALVE ITSELF

START YOUR ENGINE AND AS YOU REV YOUR MOTOR YOU SHOULD SEE THE ARM ON THE POWER VALVE MOVE. IF NO MOVEMENT YOU WILL HAVE TO REMOVE THAT SIDE ENGINE CASE AND CHECK CHECK VALVE FUNCTION....CHEERS

hi
If you have run the engine with too little oil then there is probably damage to the piston / rings & / or bore
Remove the exhaust to have a look

Ride Safe
Bike-Doc

sounds like you are running to lean,whenever you alter your exhaust system you must rejet your carb. when you have jetted correctly your spark plug colour should be chocolate brown. white or gray is to lean black is to rich.Change your jet to a larger size,install new spark and take it on a short ride at full throttle stop and check plug colour. repeat this till plug colour is correct. hop this helps james

Is this a 4 or 2-stroke?
4-stroke = bad valve seals of piston rings
2-stroke = oil/gas ratio too 'oily' OR air filter clogged.

Why 50:1?
All bikes should be 32:1, and then jet to match that.
Your oil is fine, and yes...go smaller on the pilot.

Intake 0.10- 0.20mm Cold
Exhaust 0.12- 0.22mm Cold

Black Plugs are indicating that your bike is running too rich(too much fuel to air mixture) you need to have the carburator adjusted,more air.Good Luck.

buddy this is fine brilliant compression there ment to be from 100-185psi tops if below 100si bye to rings buddy