RM125 not running right

I have a 2001 RM125 and it tries to cut off in neutral and bogs down during hard acceleration. Please help me!  

how many hours are on the bike since last rebuild?  
1997 RM125
(Thanks DirtJumper)

check compression, spark plug, air filter  
1997 RM125
(Thanks DirtJumper)

Im not sure, I just got the bike half a month ago. And I just put a new NGK spark plug in it and the air filter looks pretty clean.  

Being as it is a used bike. Your best bet is going to be to check compression as stated, And clean the carb and jets and start fresh.
Also you want to clean and oil a new air filter. Good call on a new plug, You want to start fresh as much as possable within your buget.
Also if you do not have it. Your first purches should be the service manual.  

Im new to working on dirtbikes, how do you check the compression?  

You can have a shop do it for a few dollers, Or get a compression tester from a shop or pep boys ect and pull your plug and screw in and kick the bike hard fast and smooth untill the gauge stops rising. Do this 3 times to get a good averege.
Your next question is going to be What compression am I looking for Right?      
Your bike should be at least 130.
If your in the low hundreds then a Top end Is in order. This can be done cheap by you with the manual.  

Thanks a million!  

may be running rich that will have pretty much the same symptoms. what mixture are you running? 32:1? also pull your plug and look at it. what color is it? if its black your running rich, grey your running lean, light brown your on the money. i know that when my bike runs real rich it wants to stall at idle and bogs in the low/middle rpm range then snaps to life up top.  
-Kirk 88 Honda CR250R
ride hard and crash harder

Thats pretty much what its doing. Ill have to check it. Im runnin 36:1 in it.  

i run my bike at 40;1 and my plug is still black. The plug that was in it was a ngk #5. What number plug u runnin  
1997 RM125
(Thanks DirtJumper)

try cleaning the carb.  

40:1 is close enough most run 32:1 and in a 125 i would run a NGK br9es/eg. never lean the mixture to solve a jetting issue (or run a hotter plug). thats just putting a bandaid on a cut that needs stitches. in the long run you will do more damage to your bike by run too hot of a plug or too little oil. you need to lean out the jetting. im not the greatest with jetting but someone on here can help you. if its black you are too rich and that explains the problems you have been having. replacing the top end is a good idea with a used bike but i would solve the jetting first and go from there. may straighten it right out and cost you nothing.  
-Kirk 88 Honda CR250R
ride hard and crash harder

By going to 40 to one from 32 to one you are actually making it richer. now you have more gas going in to the same amount of air.  
__________
"Every time I start thinking the world is all bad, then I start seeing some people out there having fun on motorcycles. It makes me take another look." -Steve McQueen

i did have a ngk b8egv in it but when i got a new one, they didnt have it so NAPA supposedly gave me the Autolite equivelent. And yea i have been wanting to clean the carburetor but dont kno much about them and was wondering what i have to be careful about.