I had an old 21cc two stroke weedwacker engine that I had lying around and was trying to rebuild it for use in a possible hobby project. It sat with gas for a very long time so I disassembled the carb and cleaned it thoroughly and reassembled. I did not see any damage to gaskets or internals while cleaning. The primer bulb appears fine as well. I changed out the fuel filter and the fuel lines too.

When I attempt to prime the carb since reassembling, I am not drawing any fuel into the bulb, it sounds like something is sucking air. I went to unscrew the top plate that holds in the bulb and fuel started to jet out dramatically as if there was a vacuum of pressure inside the internal of the carb. I unscrewed the gas cap to see if that was the problem and I heard air being sucked into the gas tank and the fuel stopped jetting out of the carb. When I press the primer bulb with the gas cap loose, it sucks in a tiny amount of fuel but not enough to matter.

I am wondering if I reassembled the carb incorrectly, if it is still clogged somehow, or if my gas cap is bad. Any advice would be helpful.

1 Answer 1


It could be a leak in the bulb or connected tubing: Replacing the bulb is a fairly maintenance item, like replacing a spark plug.

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