I have one of these that I ran for about 3-5 minutes Sat afternoon 10-22 fuel, then today it would only run the prime..  What could be wrong???   Using a Cox 6x3 prop both times...

Do you have enough fuel line to make a plug for one vent/filler, and force-feed the tank? Once the tank is pressurized, fuel should dribble from the screen/venturi. You want to plug the second vent before the tank is full and tip the engine so the pickup line is "on the bottom." If you do get fuel from the venturi, then you know the pickup line is in the right spot (or close), and the pickup line is secured to the nipple on the backplate.
If you don't get fuel flow, then pull the needle and squirt a good bit down the needle hole to see if the fuel hole is plugged. Another check, though even messier, is to pull the needle and while holding your fuel pump line over the air inlet, squirt fuel in. While a good bit of pressure will lift the reed valve, a light push should still have a bit of fuel bubble up through the needle passage. In other words, you are testing fuel flow through the needle in both directions. Even removing the needle and pressurizing the tank (plug one, pump the other filer again) should produce fuel flow out through the vacant needle hole...again showing the pickup line is still attached to the backplate.

A weak seal when wet, such like running rich helps seal the places the engine can leak...the o-ring between the tank and backplate, the front crankcase bushing to crank, and the part of the tank the reed seals against.

Have you been in the engine lately? Hard pickup lines can crack...so much as to disrupt fuel pickup. The red may have a bit of trash under it (see "so rich it seals" above). Also this could be a good time to try another reed...especially if you have a floppy disk you can make a test reed from. A stuck reed can do the same thing...remove the glowplug, and position the piston so it has the transfer port open from the crankcase to the piston top. Now blow some air into the venturi and feel/listen for air passing into the block under the piston and escaping out through the transfer port. No airflow means the red is stuck. You could use a syringe full of fuel doing the same thing...so expect to see fuel percilate up to the piston crown instead of air.

Go over to CEF and get Paul Gilbert's Mouse racer build guide. It has quite a few hints for the Bee engines, especially for tanks/pickups/Reed's. See the bottom left corner for the entrance to their files (under the "latest threads" column).

I'll keep watching to see how it goes for you.

PS I assume you got my AP Wasp PM, but my offer was too low.