OK, it sounds like it's not tuned properly.

Try this even though it's how I do Walbro carbs, I tuned my 3W75 this way and it works on them too.

OK, that sounds like the idle is rich. This is how I would tune it, or any gas engine with a Walbro carburetor.

1.Start the engine, set the throttle so the engine is going 3500 rpm.

2.With the engine running I turn the "L" needle in, it is always the needle that is closest to the engine, when the engine speeds up to 4000 rpm I adjust the throttle to bring it back to 3500 rpm. You keep repeating this step until your engine doesn't speed up anymore when you turn the "L" needle in.

3.Turn the "L" needle out 3/16th of a turn.

4.Open the "H" needle 2 turns out, open the throttle all the way open. Now slowly turn the "H" needle in the engine will increase in rpms. Turn the needle about 1/16 at a time, when you get no more increase in rpm the "H" is set properly.

5.Set you idle speed with your throttle trims, it's best to take the idle stop screw completely out, you should have it so the idle is correct with the trim in the middle, and the low trim kills the engine.

6.With the engine running at the idle speed that you fly at you should now be able to snap the throttle open and the engine quickly speed up. If it just dies, turn the "L" needle out 1/16th of a turn, repeat this step until is quickly speeds up. If when you snap the throttle open it stumbles then speeds up turn the "L" needle in 1/16th of a turn until it cleanly and quickly speeds up.

7.Close the hole or notch up in the choke plate, I'll post a picture of what I mean, I do it with soldiering the hole close, some use glue or a bolt.

After you modify the choke plate the way to start the engine is:
a. Close choke completely.
b. Open throttle half way.
c. Flip engine with ignition on until the engine coughs.
d. Take choke fully off.
e. Set throttle just above idle, flip until it starts, usually 3 to 5 flips.

Switch to Pennzoil 32:1 your engine will last forever.

Before and after pictures of choke plate modified, shouldn't take more than 15 minutes.