I would also check the fuel lines if you haven't already, If I remember correctly the fuel lines are two piece and run through the handle and if old are known to crack, get hard and suck air. I would also try to clean it again also sounds like the low side or idle curcuit is still plugged up or sucking air. There is a little screen under the diapharm side I thing or the other side on the inlet side the cruds up also???. I would also pull the low jet needle out and blow carb cleaner through it to see if it flows?

Last I would also go over the parts breakdown and double check you assembly this include the gasket between the carb and block.

Ref # Description
1 Throttle Valve
2 Throttle Valve Screw
3 Throttle Shaft Ass'y.
4 Low Speed Mixture Needle
5 Throttle Return Spring
6 Low Speed Mixture Needle Spring
7 High Speed Mixture Needle Spring
8 High Speed mixture Needle
9 Plug-5/16 Dia. Welch
10 Plug-1/4 Dia. Welch
11 Pump Cover Screw
12 Fuel Pump Cover
13 Fuel Pump Gasket
14 Fuel Pump Diaphragm
15 Fuel Inlet Screen, WT-3(#35158)
15 Fuel Inlet Screen, WT-20(#35181)
16 Idle Speed Adjusting Screw
17 Idle Speed Adjusting Screw Spring
18 Throttle Retainer Ring
19 Inlet Needle Valve
20 Metering Lever Spring
21 Meterin;g Lever
22 Metering Lever Pin
23 Metering Lever Pin Screw
24 Metering Diaphragm Gasket
25 Metering Diaphragm
26 Metering Diaphragm Cover
27 Metering Cover Screw Ass'y.
28 Carb. Repair Kit
29 Carb. Gasket/Diaphragm

Check the reed valve. It may not be seating properly and allowing back pressure to get into the carb. In some cases the reed valve can be turned over.