Another starting problem!

I have a 1981 Maxim 650 with 7800 miles. I think I am the third owner. The bike ran fine when I bought it, but the mileage was poor (20 mpg). Like most of you, I got busy and let the bike sit for a while (10 months, I have 3 kids). Couldn't get it to start when I had time, so I tore the carbs down and cleaned them. It ran ok, but I really wanted the bike to run well, so Chacal set me up with the parts and I read all the clean your carb posts and went to work. I broke them apart this time and replaced all the parts that were recommended. I bench synced the carbs and set the fuel level in all the bowl. It ran alot better, but would "pop" at high rpms and seemed to sputter. I took the carbs apart again and checked all the levels (I left a washer out) and put the sucker back together. Initially, it started, but didn"t seem to want to run. It tended to start on prime and then after a couple minutes it would die. Now I can't get the blasted thing to even start. I contacted Chacal about getting a new petcock, but he recommended that I post my problem before I ordered anything. I pulled the fuel line off today and fuel will flow when it is in the prime position. I'll pulled the carbs off again this coming weekend, but I'm at a loss for what to do or look for. Any suggestions? I have looked at the recent post and think I have tried everything. Thanks for any help.