Starts and idles will not run above idle unless choked. Have cleaned carb multiple times new fuel filter new air cleaner and cleaned exhaust screen new plug. Maybe a collapsing fuel line?

Sounds like lack of fuel. Try backing the air fuel mixture screw back 2 turns and see if it helps. Once it starts, see if you can keep it running by spraying carb cleaner into the carb. If you can keep it running long enough, place the palm of your hand over the carb inlet to choke the carb causing a sudden suction in the carb. Some times this will dislodge foreign material and help it run.

My money is on a partial blockage of the main jet or the passageway to it. You're having to force it to run through the idle jet by fully choking the incoming air. There's not enough gas coming in with the choke open to allow it to run.

I'm thiniking total carb disassembly, carb cleaner and an air compressor combined with a ton of patience will take care of the issue.

May I suggest checking along the fuel line and its attachments for a very minor air leak. The minute it sucks air it will stop. Check any rubber washers or O rings too.

Excess air or not enough air. Replace air filter. Spray outside of carb to clean & ensure choke movement is smooth. Water in gas may cause this also. Flush out tank, refill with fresh gas, always use Stabile.

hello sir, my machine will only start when pumping primmer bulb or squirting fluid in the carburetor than stops. the fuel line has broken off, in most small carburetors this is a ongoing problem.old fuel will crystallize when left in tank for a long time.plugging up ports, fuel lines, small screen in carburetor.fuel lines will dissolve clogging carb.this is why it will run when the choke is on creating a vacuum to where there is fuel forced in the carb to rum,also the gas will evaporate leaving the oil behind clogging up carb.the thing to do is remove carb. and clean out,replacing gaskets or fuel line if necessary.use carb cleaner to clean out carb.make sure to make note where fuel line go.the fuel filter broke off of fuel line letting debris get in carb plugging it up.the muffler is known to clog up a lot on these machines where they want run. the compression should be 60 to 120 lbs any thing below 60 is junk. when adjusting the carb screws turn in all the way than turnout 1 1/4 turns turn in slow until machine runs also you need to check for spark by removing plug and grounding against engine to check spark, ok.a new spark plug would be a good ideal too , if you are going to make these repairs use new fuel line and filter,hope this helps,any comments welcome,thank you, ==

Carburetta is fouled. Run fine on choke - rich mixture. As it warms up and choke pulls off, its starving for gas.
First try adding fuel system cleaner to the gas tank. Do NOT go overboard. No more than double the recommended mix ratio.
The alternative is to remove the carb, open the bowl and spray out the jets and venturi with carb cleaner.

Its possible you may help it by removing the air filter and spraying every orifice you find on top of the carb. With carb cleaner. Be very carefull not to flood, pool carb cleaner in intake as this is not healthy for engine either. You can do this with engine running, so as not to pool, but slowly is best, both in engine speed and volume of carb cleaner.

There is a number of reasons why this can happen, running the saw on too rich a fuel oil mix, most modern two stroke oil is ok to run at 50-1, air filter blocked creating over fueling, clean the filter, carb mixture screws set too rich, re set the H screw on the carb, carb flooding due to needle leaking, service carb, ignition system fault, miss firing, replace plug, or ignition unit.
Always try the easy stuff first before fitting new parts.

Your bike is running too lean. If you have not made any changes to the air intake or exhaust then your pilot jet may have something blocking it. (probably a piece of dirt, or just tarnish build up of fuel if the carbs aren't drained while in storage) By turning the choke on, you are reducing the ammount of air allowed into the "Fuel / Air" Mixture. This allows the bike to idle properly. Once the choke is off, the mixture has too much air and not enough fuel causing the backfire. If you haven't changed anything like the exhaust or air filter it sounds like a good carb cleaning is in order. Otherwise, you will need to change jet sizes to accomodate the difference in air flow.

Remove and clean the carb. Sitting around can let the gas evaporate. This leaves a varnish residue in the carb. Remove the carb then remove the float bowl. Use a spray carb cleaner to spray into the jets and carb circuits. Remove the throttle screw and air screw and spray into the screw holes. The low speed idle circuit is the problem so concentrate on the air screw hole. Put both screws back where they came from and turn each until it LIGHTLY seats. Now back each screw one and one half turns. This is the factory setting. If the bike still does not want to idle, there is still some varnish or trash plugging up the idle circuit.

This is most likely a fuel related problem, unless you have electrical gremlins that are screwing with your ignition unit. Does it idle OK with the choke engaged, but dies when you disengage the choke and/or when revving the engine? In that case, your air/fuel mixture is probably way too lean. Could be dirt clogging up your fuel tap, fuel line, fuel filter or carbs..?

Try running some Seafoam or similar carb/jet cleaner through your system. If that doesn't work, take the carbs out and give them a good old manual clean.