Rebuilt top end 30 over and now it starts fine but will not idle down...... what should we do?

You very well could have the choke stuck or it could have a clogged muffler unbolt the muffler and start it and see if it will rev then

Check for vacuum leaks. Spay starter fluid around intake,carb base, etc., while engine is idling, listen for change in engine idle.
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If you are lucky, you might just need new fuel filter and the fuel bowl cleaned out, and maybe new air filter. If not so lucky you need carburetor rebuilt. Backfire is usaully caused by engine running too lean ( too much air for the amount of fuel present). Fuel bowls get gunk in them and the fuel needles and fuel jets get varnished up. The accelerator pump gets worn out gaskets and/or bellows and doesn't give the right amount of fuel mist when you accelerate.

Full Choke is indicative of a motor starved for fuel

Try adjusting you mixture a little richer, 1/8 turn on the fuel screw. If this doesn't help get to idle, you will need to rebuild the carb. make sure you get a complete kit to include the float and throttle springs as well as jets and gaskets. Write down your initial mixture settings and try them again on your rebuilt carb. Should be fine. Bending float arms for travel length is tricky, be careful as they can easily break off making them useless. The rest of the process is pretty straightforward. Ensure you place the needle jet keeper ring on the correct groove and the throttle moves smoothly against the spring tension on the cable above the needle valve.

carb needs tuning

Hi Thomas only thing I can think of is that its not getting enough air is it the right filter as it may be not be allowing enough air through. As you probably know if you don't get the right amount of fuel & air it won't run right. Hope it helps cheers Paul

First question since i am assuming it was just sitting around for some time if i am correct you need to pull the carb remove the float bowl and components if everything was done correctly with your rebuild the likely problem is your carb is gummed up remove everything in the carb low speed jet etc. soak everything in sea foam fuel cleaner overnight and hopefully you have some compressed air and blow out that low speed jet and passage way pay close attention that you have see fluid coming from the other end and check the jet make sure it is unclogged hold it up to the light.

Replace idle jet with a new one OEM is $5.00. If won't idle still the compression is so low that it won't stay running Or possibly the main seals are leaking (a 2 stroke has top end & bottom end compression.)

Very vague question but I will try anyway if it died at full throttle and won't start again check the copression if it is below 90 psi it needs the top end rebuilt also when u pull the spark plug out look at it if it is whitish and dry definitely needs to be rebuilt running to lean if compression is good carb or electrical problem hope this helps you

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sounds like its running rich. check your float height and then lower your main jet needle a notch