Echo PB 610 Won't Prime

I recently purchased a used Echo PB 610 backpack blower. It worked fine for a while. Now it does not prime (and so it doesn’t run). When I push the priming bulb it pushes very easily and releases quickly. There’s a lot of air in the bulb. I removed the plastic/rubber bulb itself and that doesn’t seem to be the problem. To test it, I placed the flat surface of the bulb against a flat piece of plastic and pressed it; it stays attached to the plastic. Maybe that’s not a good test?

If the bulb is good the next thing I’d suspect are the fuel lines. I have two. One is a larger diameter black rubber hose. The other is a much finer clear plastic tube. I assume one of these is a suction line, and the other a return line. Which is which? Do these things fail very often? And which lines: the external lines or the ones inside the plastic fuel tank? I also assume there is some sort of check valve mechanism in the carb that allows fuel to flow in one direction only. Is that a common point of failure? Do I need to buy a full rebuild kit if that’s all I need?

I’ve never worked on a blower before. Any help you can provide is much appreciated. Thanks.

 

I would suspect the fuel lines, one of them likely is cracked and sucking in air.

 

I did some additional tests. The small clear fuel line is the return line. When I disconnect both fuel lines at the tank and pump the purge bulb fuel squirts from the clear line. If I cover that line and pump the bulb I feel a puff of air when I remove my finger from the end of the line. So I'm quite certain that's the fuel return line.

So I'd expect to feel some suction on the larger black line when I let the purge bulb relax, since that must be the suction line. That didn't happen, however. So I removed the black rubber line from the carb and placed my finger directly on the brass pipe coming out of the carb and I still don't feel any suction. It seems like one of the check valves in the carb is bad.

Do you know if the check valves are inside the purge base, or is that function provided by diaphragms inside the carb?

 

Most of the time the check valves are in the base that the primer mounts on. They could be causing a problem, and sometimes they need cleaning.

 

This carb (Zama C1M-K76) has an opaque white plastic base that apparently contains the check valves. Except for the two orifices that lead to/from the valves they are totally hidden. How do I go about cleaning them? I see no way to disassemble the molded plastic piece. I removed both covers from the carb and the inside of the carb looks really clean. But I guess some crud could have gotten into the check valves.