On one side of the diaphragm is the regulated propane gas, and on the other is air from the atmosphere. During operation, a flexible diaphragm within the regulator moves back and forth in response to engine demand. The LP generator has a regulator to meter the high-pressure gas from the propane storage tank at a much lower pressure to the intake manifold of the generator's internal-combustion engine. I added a brass screen (from a garden hose washer with a built-in debris filter) to inhibit future critter-related obstructions. Clearing out the hose and replacing it fixed the problem to this day. Simply removing the hose allowed the genset to start easily. The most commonly cited culprit is insects, especially mud dauber wasps who build mud nests inside the normally open end of the hose. Online research eventually revealed a common cause: a restriction of the 'regulator vent hose' on the generator. We had not run it in many months (we are infrequent generator users).
In the middle of a 7,300 mile circuit of North America in 2011, we discovered that the Onan MicroQuiet 3600LP generator in our 2006 Itasca Navion wouldn't start.
