Carb problem baja 125 motorsport idels fine when throddling up it dies

the idle circuit in the carby still has a blockage that is preventing it from allowing the fuel through
compression is good
possible that the ignition timing is not correct
at this point I would suggest that the carby be overhauled by a Evinrude service shop as rubber from hoses , fuel pump breaks down and fine particles get into jets and passages and block up the holes

clogged pilot jet in the carbs causing a lean condition and backfiring

In general, yes. This is a carb tuning issue. Another possibility is a vacuum leak somewhere, but most likely, it's a carb issue. You'll typically see your rpm drop a bit when you put it in gear, but that it sometimes stalls out points to a carb issue.

if you are sure the carbs are ok then check the linkage for wear, i had one do the same thing cause the carbs were not in sync and one cyl is fighting the other

Try a new spark plug. Go to a motorsports dealer to purchase a new one as alot of discount or big name store can get a lower grade of sparkplug and this can create alot of grief.

ALWAYS have a fire extinguisher at hand when working on carburetors.
Remove the water trap bowl at the bottom of the petcock, (gas valve). Is there any water or trash in the bowl? Drain a cup of gas from the tank. Is there any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).

Drain the carburetor. There may be a screw on the lower side of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install a new stock NGK spark plug and try to start the engine. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the idle screw and the air screw on the outside throat of the carb and spray into the screw holes as well.
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Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two adjusters down. Only screw these in until they LIGHTLY seat. Now turn each adjuster one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine. This process should get you back on the road.

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Hi ..... Any motor vehicle can be made more efficient or faster, what would you like top achieve ? Faster acceleration, top speed or both ? It's usually a compremise. I think the bike you have is a bored out 125 (factory designed 125) so any benefits will be marginal.Top end and accelleration can be achieved by gearing, which is relatively cheap but as mentioned before is one or the other. More expensive mod's would be increasing the bore (bigger piston), skimming the cylinder head (raising compression), flat slide carb and performance exhaust .......... by spending alot of money and time you could have a fast (say 180 cc) that'll be as good as a 250cc bike ................. Let me know if this has been of help and I can/will go into more detail.