Hope someone can share some knowledge here..
My Onan gas 4000 will not start. Some history, Changed plug, air filter, and removed exhaust plugs/(clean), and serviced in Oct. Ran fine mid-Oct. Sat till early December. Has 2 6v. batteries to start, which are fully charged. Hit the prime and get a click,click, click with the engine just cranking with no start. Checked voltage, and batteries are over 12v. To the best of my memory, (cause it's stored @GDS), I think I got an overrun code, but can't be sure. Fortunitely, I keep my honda 3000 with the trlr, and it has been my house power up until now. Any ideas why this clicking is? Is it a fuel pump or starter issue? Any comments will be greatly appreciated.

Mine has done that when the batteries are too low. Jumped it from the truck and fired right up.

I will try that, I hope it's as simple as that, the batteries were new, but could be not enough to start. Thank You blackdmax.

We just had a problem with our 5500 it would start but die as soon as you let off the start button. We had a bad fan belt. I didn't know these had belts.

I had a similar problem and it was a valve spring. There is a mobile generator/rv guy that is not to far from you. His name is Rob (760) 224-2351. He fixed my generator in Glamis at my storage. Very reasonable and does great work.

i just had the same type of symptom last weekend

crank crank crank no start fuel pump clicked loudly like it wasnt getting fuel
after giving up i walked to the other side of the trailer and noticed fuel dripping under the trailer, after getting underneath it appears that the fuel line shrank from sitting and pulled the line off of the filter
the line was now about 4" too short!!!! i have never heard of this problem before just throwing this random bit of info out there

Also could be a small hole in line that is sucking air. replace the fuel line, if your trailer is over 5 years, that rubber house will go bad.