whemme wrote:
My vote is that you have a weak/inoperative electric fuel pump on your Onan generator
I lean towards this too.
So many people go right to the carburetor when there is a problem. There are countless replies over the past 14 years I have been hanging out on RV forums, people saying "It's Your Carb", "Use Seafoam", Replace Your Carb".
For the past 32 years, I have been living in a house on an acre so I have a 18hp lawn tractor, 8hp roto-tiller, 8hp snow blower, and a 5hp power-washer, all of which are 4 cycle engines with simple carburetors. The tractor, tiller and snow blower are 32 years old. When I am done with any such equipment for the season, I simply place them aside. I don't do any storage preparation what-so-ever including never adding a fuel stabilizer. When I pull them out to use them as needed, I check the oil level or change the engine oil if it's time, and clean or change the air filter. I top off the fuel tank and they initially start rough, but after a minute, they smooth out and are ready to get work done. For the past 14 years, I have always applied the same practice to our Onan, yielding the same good results as my yard equipment.
Due to becoming "involved" grand parents along with world travel, this past summer marked a two year period since I previously started our motor home or our Onan. Two years was the longest duration yet so I was a tad bit concerned. The motorhome is stored indoors so I was fairly confident all would be well and I was right. The Ford V10 engine started instantly and smoothly as if I had it running an hour earlier. With a lot of priming in advance, the Onan started up fairly quickly, and behaved as it always did, requiring a minute or so to smooth out.
This past summer during that awakening, after 20 minutes of running properly under load running the a/c unit, my Onan suddenly shut off. After some research, I narrowed the problem down to the fuel pump. It became sensitive to working when it is very hot outside. When the day cooled off, the fuel pump worked fine. I have a new fuel pump and filter ready to install prior to our next trip.
I think much of the reason why Onan recommends running the generator once a month is because some are stored outdoors in very high humid environments. Running it as recommended might be for the sake of the power generating portion of the unit, not the engine itself.
As far as a "gummed-up" carburetor is concerned. Today's fuels are formulated to avoid that varnish that we dealt with in the days with carbureted automobiles. Vehicles today with high pressure fuel injection systems cannot tolerate "varnish" and such, so the fuel is so much cleaner than years ago. This "clean" fuel benefits small engine carburetors. There is no varnish build-up. There could be dirt build-up from a leaking air filter, so carb cleaners like Seafoam does have it's use. 2-cycle engines with oil in the fuel benefit greatly from carburetor cleaner products.
In many parts of the USA, fuels include a certain amount of alcohol. That cleans things better yet leaving even less residue in the carb as it evaporates away during the storage period, but the additive is hard on rubber gaskets and seals and such in many carburetors. It tends to dry them out, stiffening them, and in a worst case scenario, it cracks the rubber seals. My 1983 Toyota pickup truck I owned for 24 years, had a diaphragm in the side of the carb that the alcohol would dry up to the point that it no longer would move as it was supposed to. I had to change that part every-other year because of the alcohol in the fuel. Around these parts, I cannot buy gas without some amount of alcohol.
