Why it won't it stay running

Dirty screen in carb

first I would replace spark plug, I dont know how old your fuel is, but here are different types, some burn hotter, some cooler, but a gallon of that fuel does not stay good over long periods.

I need help! My son mx650 is charged, but won’t run. Put weight on it won’t move but lift rear tire off ground and runs full throttle

need your carb rebuilt or your carb readjusted. sounds like you might have some mud in it. do you take it in the mud? if so check the top where the throttle cable comes through.

clearly sounds like fuel starvation, I would be looking at the throttle body, they need servicing every couple of years, they fill up with like grease and block tick over hole.....

Only Info I see is "Homelite Chain Saws" - not much to go on.
Most saws have two carb adjustment screws, Hi, and Lo.
Assuming the saw will start and run enough to warm up, then
adjust the Lo screw in, clockwise, until the motor starts to slow down,
turn only about 1/8 turn at a time. From the point where it starts to slow down, turn it out about 1/4 turn. This should give you a decent idle. Now pull the throttle, and see what happens.
A - Saw runs up to speed, but dies off, or starts to slow on it's own.
turn Hi idle screw out about 1/4 turn.
B - Saw speeds up, but runs sluggish, fat - not real hi end.
Turn Hi screw IN, about 1/8 or so, and try again, or adjust
while running at full throttle. (best way)
IF it won't run well, try turning both screws all the way in to seat them, then come back out about 1-1/2 to 2 turns. this should get you in the ballpark to set things up as above.

Once the saw is running well, adjust the idle screw to a smooth idle but slow enough that the chain stops moving.

Stay safe

If it is a 3.8 engine change the crank sensor,they go bad on the 3.8 engines.

first ensure your spark plugs, wires, cap and rotor/coil packs are in good shape. once thats done check for a check engine light, sometimes they come on then go off but a code will be stored regardless. once you have made sure your getting good spark and there are no trouble codes the issue is most likely a dirty throttle body or fault IAC (idle air control) valve or throttle positioning sensor. hope this helps, good luck

Is the engine running at high idle or are you having to hold the throttle open to keep it running? If it stays at high idle on it's own be sure that when you push the choke back to the "off" position, check your linkages and be sure that the choke cam is returning to the low idle position, also be certain that your throttle grip operates without obstruction when returning to idle position. If you are having to hold the throttle open to keep the engine running you are probably going to find carburetor issues. Hope this help to get you looking in the right direction.

96 , TRACKER?
IF IT RUNS AND STAYS running. then that means the car is flooding or is in a sad state of tune.
tune it up and it will start every time.

if not ask me here.

http://www.kick-fix.com/
see my guest book. ask a question.

1; tune up
2: bad ECT sensor.
3: stuck closed IAC.
my page answers all sidekick questions.