bike wont start just backfires when kicking

i have a 90 rm 125 that i just bought it was running and starting fine except by the time i would get to 3rd or 4th gear it would bog down and die then take a minute to start back up and do it all over again so i took apart the carb and discovered the arm that closes the needle seat valve was upside down so i flipped it over and the bike ran great i made 3 or 4 passes on a straight away and suddenly the bike just shut down no bog this time and now it wont start it just backfires every 5 or 6 kicks not loud just sounds like its letting out ideas?

well i got it starting on the first kick again i took the tube that goes from the filter to the carb off and kicked it 10 to 15 times it started i shut it off and started it a couple more times so it seems to start perfect air filter seems to be new or in very good condition im now curious what the issue was and how to prevent it

most likely a differnt issue. than fuel related... If it does it again..pull the spark plug and see if it has quit firing. If so unplug the kill switch.

it did it again i checked the float level and it was way off so i fixed that but now its been two days and i cant get it to start...throughout this whole time ive been pulling the plug and i have spark

I had same problem with my 98. First check flywheel and make sure it is not loose. 2 (which was my problem) take off power/exhaust valve cover and see if both valves are free and moving. One of mine broke and slammend into the piston and dinged the ring. So it had low compression. Like 110 ring and new valve. All fixed.

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