85 720 Fuel problem

Hi all, I have the 85 truck with fuel leak problem. I replaced the fuel line from the pump to the carb. I can idle the truck for 15 minutes no problem. When I take it out around a few blocks fuel starts running out the accelerator pump housing. The sight glass in the front of the carb during idle is fine( 1/2 way up). When I get back after a short drive the entire float section must be full as the glass has no fuel line? Seems as if there is fuel flowing with no stopping and filling up the carb and the pressure builds up? Looks like the to and return line are tied together at the carb? A past responce was the needle and seat was blocked by some dirt. Could this cause this problem still with the full fuel and pressure? Could the return line be blocked enough to let it idle, but not drive under a load? The front of carb with the sight glass has 3 screws on the cover. Will this get me to the needle and float to check things? Thanks for any help. Jerry

It sounds to me as if your float is stuck. I would first check the needle valve and seat. Then I would check the float itself and see if it leaks. The most direct and simplest cure would be to swap the carb for a rebuilt unit. These still need adjustment however so if you're not up to that task, having it rebuilt by a good shop is your next bet. Your carb is 21 years old. Seals age, seats get scarred, dirt gets into hidden passageways. A rebuild is definitely in order. the leak you describe seems to be triggered by heat coming up through the carb body. That heat will change the relationship of how certain parts fit each other. If they are at all warped, which certainly does happen with carbs, you will get a leak like that and have a devil of a time chaseing down the cause because at idle or when cool, it doesn't exist. Again, a rebuild is the cure.