There's no low speed needle on the LA, just an air bleed. You are not getting enough fuel somehow. Sounds like a leak or a pinched line. It could also be from a really low tank as mentioned above or excessive fuel line length. Also check all of the screws on the motor and make sure they are tight. Those plastic fuel nipples really don't seal well and can cause problems. Try some small hose clamps. Where is your needle set?

I've purchased 2 LA's and they will be my last LA's ever. I love the old FP's.