How to you properly adj a 2-stroke carb on a motorcross bike to keep from fouling the plug

is the bike a2 stroke or a four stroke? regards Ray.

Make sure your spark plug is not fouled and the gap is correct, also air filter is properly cleaned. If it still wont idle, locate the idle adjustment on the carb. There are 2 screw type adjustments there, one is the idle/air screw and the other is idle adjustment which is the one you want. Start the bike and warm.it up, slowly turn the idle adj. Inward like tightening a bolt, periodically give the engine a slight rev and let it idle.down. Do this until you reach the desired rpm you want to idle at and your finished

Fouled plugs are typically caused by jetting that is too rich. This could also be from a dirty air filter which can make the bike run rich. Clean up your filter and see if that is it. If the filter is not too bad, you might want to drop a size on your pilot or main.

Another possibility is poor compression - this can make a 2-stroke run richer than normal as the fuel can not be burned properly. Rings don't last long in these 125s. I used to re-ring each week when I was racing 125s.

You might want to run a B8ES plug, too - this is one step hotter and will help the plug from fouling as often.

try changing gas . dont forget to empty out carb bowl also check for spark might have a fouled spark plug .

NGK BR9EG is the stock plug for your bike. You are one heat range hotter already. I suggest you go to a BR8EG to keep you in the racing plug style but one range hotter than stock. I question what 2 stroke engine oil you are using. Stick with Yamalube 2 stroke oil and you should be okay. If you are using standard motor oil like you have in the gearbox then the fouling is definitely the oil.

Are you losing gear oil.
When the crankshaft seal leaks, oil from the gearbox is sucked into the crankcase, and this can foul the plug.
Also check the plug gap, most guys set the gap too small. It should be 0,7mmto 0,8mm. The plug should be a B9 EG, or equivilant.
Now, you can also change the plug cap to a type that has a built in resistor, this also helps with plug life.
Note that 2 strokes use plugs way more than 4 strokes, and you should replace the plug every 15-20 hours to keep your riding pleasant.
Good Bike you have there
Cheers
Jon