For your dirt bike to run you need 3 things:
1. Fuel (gas/air)
2. Compression
3. Spark
Start trouble shooting through these. Make sure your gas is turned on, and that it flows through the carb; if you tilt the bike does fuel run through the overflow tube in the carb? Make sure you have good spark; take out the spark plug from the cylinder, still connected to the ignition wire touch the threaded end to somewhere metal on the engine and turn the bike over. You should see a spark. Finally, do you have good compression, how hard is it to kick over etc.
These are the first things to trouble shoot, I would look on youtube if you don't know what you're doing, there are plenty of helpful videos there. You can also try putting a thimble full of fuel into the cylinder and then kick it over to help it start if it has been sitting a while.
Have a 97 Rm125 just bored it to a 134 did everything right have gas , spark, an awesome compression But wont start ... i got it all back together it started for like 10 seconds then shut off an wont start at all now
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SOURCE: have a 1992 suzuki 125 rm bike cant get it to
try changing gas . dont forget to empty out carb bowl also check for spark might have a fouled spark plug .
SOURCE: My 97' rm 125 after
The description given indicates a lean fuel / air mixture. This is usually caused by rubber seals going bad between the carb and the cylinder. Air that has not gone through the carb is mixing with the air/fuel that has gone through. First check that the two air vent hoses coming from the center of the carb fit tight. Then that the carb fittings at the front of the carb are tight and that the fitting on the cylinder is tight. If the mounts are tight the seals are leaking. Replace any gaskets, "O" ring seals and rubber manifold fittings between the carb and cylinder.
SOURCE: I have a 2001 Suzuki RM 125, it won't start
hi mate i had a rm 250 with the same problem, have you done a compression test, as mine had poor compression
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