Fuel Problem Starts-idles fine. Push to wide open throtle and it boggs, then backfires through the intake(carb) and dies (like fuel starved-lean). The short story. I have an identical unit and it runs fine. Used it's carb-same problem. New plug, valves were fine at .002'' and .004'' as per factory. Compression is 160 lbs. Rebuilt the carb early but didnt find anything. Been around this stuff a long time but this one has me baffeled. Oh yea, I blew into the carb vent line as it started to bog and it momentailry picked up. Pretty sure it's lean. Carb is the butter fly/ retangular slide Mikuni.

Fuel starved, carb should have an idle adjustment which sounds like it is fine. Look for the second adjustment

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

it sounds like its starving for fuel, when it runs lean you will get backfires and if its running rough then it may be starving for fuel at idle. Try adjusting you mixture screw and see it the engine will smoot out. Your carb my be dirty and not allowing enough fuel through it.

What engine ? 4.3 , 4.8 , 5.3 or 6.0 l What fuel injection system ? What is the fuel pressure ? Do you know what fuel trims are ? The fuel pressure regulator's are prone to leaking to leaking on thses SPI injection system./
How to identify and repair leaking fuel pressure regulator GM CPI system...

As mentioned above, engine could be starving for fuel; but
also consider ignition system - as engine makes more power, maximum cylinder pressures increase. A higher spark voltage is then needed to ignite mixture (at a few degrees before top dead center... top of piston travel).
If coil is weak, plugs fouled, or plug gap too wide, adequate spark may not occur. This may cause missing,
loss of power, sometimes backfiring (backfiring may occur if timing is off, or intake valve leaky, also). If you replace the fuel filter, 'kit' the carb, but problem remains,
look to ignition system.

Diagnostic process - put a fuel pressure gauge in line, where fuel line enters carb. Rig so can see gauge, while driving. Have a passenger watch fuel pressure as you drive; especially while accelerating. If fuel pressure drops during acceleration, then its either fuel pump or filter. If pressure remains stable, consider carb issue.
If possible, test with exhaust gas analyzer, while engine
under load (possibly at an emissions test place). If lean under acceleration, its a carb problem. If not, look at
ignition system (emission test diagnostics should help here, also). Oh, and one thing I did once.... forgot to release parking brake..... duh.

Best of luck !

Conected to the rubber induction boot is the impulse hose, it is a short curled pipe, make sure this has not split and is conected to the two nipples on the carb flange.

If your bike boggs down when you attempt to accelerate, it usually indicates that it is starving for fuel. It could be many things..an inline filter, trash in a jet, a stopped up strainer in the gas tank, excessive plaque in the carb. You can try some simple fixes such as replacing an inline filter, (if you have one). But usually the fix will involve removing the carb and soaking it in carb cleaner, replacing seals, gaskets, blowing out the jets, cleaning or replacing the lines. If your bike idles ok, but when you throttle up it boggs, you are getting enough fuel to make it idle, but not enough to accelerate, so when you call for more fuel, (accelerate), and it can't get it, the mixture leans out, (has too much air and not enough fuel). Hopw this is helpful. Good Luck!

does this happen all the time or just sometimes?if it happens all the time you need t change your spark plug sometimes you probally have water in the gas drain the carb bowl the little flat head brass screw on the bottom of the bowl make sure your gas is on to flush it out buy some stabil ethonal treatment and run it every tank fuel good luck

When it starts it is running on the idle jet and when you open the throttle it is being starved of the correct gas/air mixture. Sounds like you have a blocked air filter or fuel restriction. Take off the air filter and try to start it opening the gas slowly. If that doesn't work, clean the fuel tank filter and try again.If that doesn't work, remove the carburettor and clean it with carb cleaner paying attention to any fuel or drilled holes in the body. Blow it off with compressed air and replace it. Ensure fuel tank has clean gas.