I have problem starting my xr 250(enduro)getting good spark plenty compression,fuel getting thru and carb all clean, ?? have changed cdi unit(original duff) but it was off mtx 125 but gives good spark, bike will sometimes start but when throttle is added it cuts out, getting very frustrated, thanks jim

is the spark getting to the end of the plug or the end of the cable

spark plugs, fuel filter, carb, coil, ignition, fuel line. Any of these could be wrong and even quite a few other things could be wrong. More information on what it does and does not do when you try to start it is needed. Does it have compression, does it have spark, does it have clean fuel. Has this been stored for a long time?

Clean your carb, tank and fuel valve. When these get gummed up from old fuel, it causes these problems.

Hi
If the kick-start is seized or lacks resistance when you try to turn it then the mechanism will have to be investigated
If the kick-start feels normal, the spark is good when kicking her over & the performance is well down then there is probably a lack of compression

Ride Safe
Bike-Doc

clean the carbs

try a new spark plug. if u fowl out a plug some time they will not fire under compression.2 strokes need. fuel,fire and air, very simple engines.it is possible crank seal are bad .that doesn't allow the engine to create vacuum in the crank case.thus fuel and air will not make it to combustion chamber.

you need good compression ( at least 90 psi , kicking it with the throttle open) , good crankshaft seals for sucking the fuel/air into the botton end, proper point gap and timing set for spark ( spark should be big and fat,if not the source coil is weak,, this is a flywheel magnito ignition and it needs no battery to fire the plug) if you clean the carb, make sure you also clean the choke pickup tube or it wont choke. also make sure you have the slide installed in the right direction ( not backwards and the idle is not set too high at first...compression/****-good spark at the right time-proper fuel/air ratio and it will run

Compression release stuck open? Do the plugs show spark? Is the slide in the carb moving up and down when you turn the throttle? Soak the carbs in denatured alcohol for 30 minutes, then clean them with spray carb cleaner. Remove the air screw and throttle screw on the carbs and spray into the holes. Reassemble and LIGHTLY seat the screws. Now open each one up one and one half turns. This is the factory setting. Install an in-line fuel filter to keep trash out of the carbs. Is the exhaust clear? Is the air filter clean? Some bikes have an oil level sensor > is the oil level in the gearbox where it should be?

If you have a spark, but weak. It is possible that your flywheel is demagnetised. Then you'll need a spare.
If sparks are good, then the spark plug should be moisted with fuel after a few ( 10 ) choke kickstarts. If so you'll have a weak compression. Then you have to at least clean out the piston ring grooves ( dismount cilinderhead and cilinder ), or even change the piston rings or overbore the cilinder and place a new oversize piston kit.
If spark plug stays dry when kickstarting, the carburettor is faulty. Clean it out, check also the choke system. Check the air intake between carb and cilinder for air leaks.

make sure theres no **** on the bottom of the gas tank blocking the intake to the carb.