Thanks Rudedog. I have to say that much of the credit goes to Bob ("Nevada Walrus" on The Lawn Mower Repair Man's POWER FORUM). I did the research and the work, but it was his helpful tips that got me over my stumbling blocks. There really wasn't anything I couldn't do for myself once I figured out how everything worked...with Bob's help.
One bonus that came out of it: I realized that my carburetor was actually in pretty good shape. There was very little gunk or goop in there, except a tiny bit in the bottom of the float chamber. That's pretty good for a mower that's seven years old. Actually, the weakest parts of the carburetor turned out to be the two main nozzle gaskets and the primer bulb valve gasket.
After that, I'd say the next weakest part is the primer bulb itself. Mine was showing some signs of wear---there was some cracking in the rubber at the fold above the base; however, it was still in decent shape...no holes, and it still would have primed the engine properly if the valve gasket hadn't self-destructed. My recommendation to anyone who replaces the primer bulb is to replace the entire assembly. The O-ring gasket on the plastic valve is definitely the weak link in that sub-system.
In retrospect, I might have been able to tell that the O-ring gasket had failed if I had understood how the primer works. I didn't, but I do now. There's no fuel behind the primer bulb. It draws in air from the breather tube through the primer valve, and when you first push the bulb, the base of the bulb collapses first and pushes the valve closed. If the O-ring gasket is intact, the valve gets a good seal and prevents the air under the bulb from escaping back through the breather tube. But the valve won't seal if the O-ring gasket fails.
Then you keep pushing to actually squish the bulb flat, and that forces the air out of the bulb. That pressurized air passes through a port at the base of the bulb and runs down through an opening at one of the Welch plugs in the top of the float chamber. That air pressure in the headspace at the top of the float chamber forces fuel through the various fuel ports and into the carburetor throat...and that's the prime that starts the engine.
I could tell that the primer wasn't working. It just didn't feel the same; there wasn't the same resistance that I usually feel...and of course the ultimate proof was the fact that the engine wouldn't start. But I now realize that the fact that there was no resistance when I pressed the bulb meant that the valve gasket had failed, and all the air was leaking back out through the breather tube.
If the primer bulb doesn't feel right, it probably means that the valve gasket has failed. It's such a skinny little thing that it probably has broken, which means it could be floating around inside the carb plugging things up. Next time I'll know better. :wink:
One bonus that came out of it: I realized that my carburetor was actually in pretty good shape. There was very little gunk or goop in there, except a tiny bit in the bottom of the float chamber. That's pretty good for a mower that's seven years old. Actually, the weakest parts of the carburetor turned out to be the two main nozzle gaskets and the primer bulb valve gasket.
After that, I'd say the next weakest part is the primer bulb itself. Mine was showing some signs of wear---there was some cracking in the rubber at the fold above the base; however, it was still in decent shape...no holes, and it still would have primed the engine properly if the valve gasket hadn't self-destructed. My recommendation to anyone who replaces the primer bulb is to replace the entire assembly. The O-ring gasket on the plastic valve is definitely the weak link in that sub-system.
In retrospect, I might have been able to tell that the O-ring gasket had failed if I had understood how the primer works. I didn't, but I do now. There's no fuel behind the primer bulb. It draws in air from the breather tube through the primer valve, and when you first push the bulb, the base of the bulb collapses first and pushes the valve closed. If the O-ring gasket is intact, the valve gets a good seal and prevents the air under the bulb from escaping back through the breather tube. But the valve won't seal if the O-ring gasket fails.
Then you keep pushing to actually squish the bulb flat, and that forces the air out of the bulb. That pressurized air passes through a port at the base of the bulb and runs down through an opening at one of the Welch plugs in the top of the float chamber. That air pressure in the headspace at the top of the float chamber forces fuel through the various fuel ports and into the carburetor throat...and that's the prime that starts the engine.
I could tell that the primer wasn't working. It just didn't feel the same; there wasn't the same resistance that I usually feel...and of course the ultimate proof was the fact that the engine wouldn't start. But I now realize that the fact that there was no resistance when I pressed the bulb meant that the valve gasket had failed, and all the air was leaking back out through the breather tube.
If the primer bulb doesn't feel right, it probably means that the valve gasket has failed. It's such a skinny little thing that it probably has broken, which means it could be floating around inside the carb plugging things up. Next time I'll know better. :wink: