Bought a used 2003 250ex, sat around for couple years not used to much, paid $1500 bucks. Got a pull starter for it , new key and switch. ran good for couple weeks, now it starts sometimes runs bad like the choke was stuck. cleaned the gas tank had rocks in there, cleaned the carb 4 times with gas and air compressor. ajusted the valves, still runs the same. has good spark. took the head off the engine looked at the valves and they look closed and look good. start it up and air coming from engine out of the carburator.

 

Your post is a little hard to follow,so I am to take it that you cleaned the carb with gasoline? that wouldnt do much for any dirt or varnish in there, a carb that sat that long probably has some dried up gunk in there, you need a good carb cleaning solvent spray to loosen that stuff up and clear it out. Make sure you pull the jets (especially the pilot jet) and clean them spotless, or it will idle poorly. Also make sure all the ports are open by spraying carb cleaner into every hole and making sure it comes out the other end.
You took the head off, did you make sure to retime the engine when you put the cam chain back on? sounds like you are blowing compression back out the carb, which would mean the intake valves are open during the compression or exhaust stroke. First thing, please write clearly what you have done, and the problems you are seeing so we can understand and help you. Second, put your engine at TDC and double check your timing marks.

 

Ok first thing I did was clean the carb, it would leak gas from the over flow, didn't have carb cleaner so just used wd-40 and gas to rinse it out. took the bottom bowl off, took off the jets one was cloged, poked out the holes on the jets made sure u can see through them. Took the flote off and cleaned that small valve under the float. sprayed all the holes, air holes, choke holes, gas holes, with wd-40 and used air compressor and blow in all the holes and did that 4 times. Honda runs the same, but carb quite leaken gas from over flow.
second thing I did was change the oil, put it on TDC ajust the valves to .oo5 with feeler gage. did compression check had goog compression. still run the same hard to start, but it would start, with the air box off I could see the choke was working but air would come out from the carberator.
third thing was took off the valve cover and the head of engine, left the cylinder on. The valves looked closed, thought one might be stuck open, cleaned with brass brush and rinsed with gas. I made sure cause I could see the top of piston, put it on TDC put it back together check the valves make sure they are .005 and still runs the same, air coming through the carb. I'm not sure about the timing cam on this model, I use to ajust them on ATC 200x and trx300 change their valves. If u have any great advise I will be a happy camper.

 

How do u ajust the timing on these models, when I line up to the t mark for TDC both valves were not loose. The intake was higher then the ex one. How do u check timing??