Re: Testing Common OMC fuel pumps

[Don]

Well, there is some merit to all the view points I guess. I agree with Frank though, running an engine out of fuel at idle speeds will not damage the powerhead. But, like you say, the diaphragm movement surely does accelerate quite a bit just before the engine runs out of fuel, which may damage the diaphragm. I remember hearing the VROs clack up a storm when I used to run them out of fuel while fogging, I DID break a few air motor diaphragms so I stopped that practice.
I still run the small engines out of gas, and feather the choke just like you do, in an attempt to get most of the fuel out of the bowl. But, there is always a little bit of fuel left in the bowl in spite of these efforts. I always pull the carb drain plugs (if equipped) after winterization, especially if the engine will be in storage for more than just the winter months.
I don’t know if your rash of fuel pump failures is coincidental, or somehow related to the fuel you are using. If all the pumps had failed diaphragms, then I might be inclined to suspect running out of fuel might have something to do with the failures. Keep in mind that an engine that sneezes/coughs a lot is more likely to damage the fuel pump diaphragm as well. As fair as a fuel pressure gage, well you could sure set up a gage to check the engines, but you will need a gage that reads low pressures well, like a zero to five PSI gage. Keep in mind that checking just fuel pump output doesn’t mean a whole lot unless you rig up a clear hose and vacuum gage to the fuel pump inlet as well. Restriction/inlet air leaks are often misdiagnosed as fuel pump problems. So, I don’t know if checking pressure/vacuum is a realistic procedure for every engine you work on, rigging up these things can be a real pain due to stiff hoses and flimsy plastic connectors. Needless to say, doing these checks is not that big a deal if you are replacing the engine fuel lines anyway.
Many OMC fuel pump failures show up as engines that run out of fuel at lower speeds, but may run OK at higher RPMs. And, just like Frank says, sometimes we introduce problems by running the engines in test tanks with the fuel pump mounted 2-3 feet below the engine.