I found a fuel line connection diagram for a model 770r. It had basically the same connections. The pattern is:
1. Top of carb to primer bulb suction
2. Fuel tank connection (the one with the filter on inside of tank) to bottom of carb
3. Primer bulb discharge to fuel tank connection
The primer bulb pulls fuel from the carb and pumps it back into the fuel tank. This causes a vacuum in the carb that pulls fuel through the carb from the fuel line connected to the filtered fuel connection.
I connected this up and my Ryobi 790r weedeater started right up.
I had tried several different patterns and got close but not exact. I kept trying to pump fuel from the fuel tank through the primer bulb to the carb.
BTN
May 2009