Have you checked your carbie bowls for junk? May be a sticky needle/seat junk caught in it, could even be your fuel pump diaphragm. Need more info on what it is doing, can you rev it passed idle or does it stall?
Just had a marine ctr do a carb kit rebuild. You can rev it past idle at times but normally it stalls. I have noticed that it does not seem to hold a prime. The bulb will get firm as it should but after it runs a few seconds the bulb is weak and I have to pump it up again to restart.
The inline connectors can go bad and suck air.
The bulb should go soft once it's running.
The low speed is probably the air screw needs adjusting.
Remove the screw and check for damage, grooves or nicks on the taper.
Then insert the screw.
Tighten lightly.
Then out 1 and 1/8th turn out.
Start and warm it up.
If it doesn't run turn the screw out another 1/4 to 1/2 turn.
Then warm. Screw in till the motor buck or stalls then out 1/2 turn.
