I posted this in another area and realized it after the fact that it should prob be in this section any help would be greatly appreciated.

Hey fellas,
I picked up an 02 250ex for my son. It needed some work the handle bars where bent and brake/reverse leaver was broken and it was missing th air box it has the filter attached directly to the carb and the baffle and internals was removed from the muffler. I checked the oil after I got it home an it was empty or basically empty. Dipped the stick and with the dipstick screwed in you could barley see oil on the bottom of the stick not even on low level. I added the proper oil to top it off about 1/2-2/3 a quart and tried to take it for a ride and it went I in to first fine but trying to get it to second it didn’t want to engage no matter how much pressure I put on the shifter. It goes into reverse fine too but first and reverse does kind of jump when you get it in to gear. When it’s running if I get the rpm’s high it will go into the next gear and I was able to go through all the gears. But the rpm’s have to be up there to change the gear and even then it’s very hard it kind of slams into the gear. When it’s off it will run through the gear’s no prob. I changed the oil completely because somebody told me that dirty oil could be the prob the oil was very black but no metal shavings in it but it didn’t fix anything with the shifting. Any help would be greatly appreciated. Please excuse me being a newb. I have ridden a friends 250ex recentley so I know that it’s my machine not my riding.