Them onans are great gens! one thing that always kills them is the valve lash adjustment, the valves seat into the block and the lash becomes tight then they don't fully seal and the exhaust valves and pressed in iron seats get very hot and eventually the seat will drop out of the block. The oil filter is very universal its the same as any other onan, briggs, kohler, my 87 dodge dakota 3.9 used the same filter, my sisters 2011 focus uses the same filter etc, its a fram PH3614 or a wix 51348. also the valves being tight will cause it to run rough and sometimes hard start.
The problem it had would be that it would bog down and recover repeatedly sometimes until I put a heavier load on it, which I guess messed with the throttle. Sometimes it would stall and not hardly want to restart. But.... that was possibly all caused by the crap fuel pump?
When I first put it on it was fairly ok aside from the bog/recover. The more I used it, the worse it got to the point that it would stall after about 10 minutes and not want to start again until it sat a while. Overheating crap fuel pump? Finally it just quit, dead fuel pump.
There is a dedicated fuel gauge for the gen's gas tank next to the inside start/stop switch but who knows how accurate it is. It could be that cheapo pump couldn't handle being run dry for any amount of time pulling gas to the gen. This thing has to run gas a long way (about 15-20ft of hose). An in-line check valve near the tank might be a good idea, and not letting the tank run below 1/2 a tank on the gauge.
I have a cheapo in-line clear plastic fuel filter near the fuel pump between the tank and pump to keep trash out of the pump, so I know that isn't what killed it.
I haven't touched anything on the gen except cleaning the carb bowl/jet (I was able to do it without removing the carb because I can't figure out how to remove the carb!), adjusting the choke wheel(?) next to the carb, and the fuel pump/fuel line. The old fuel pump was seized up when I got the RV and the guy was in an RV park with full hookups, so he said he never ran it or tried it. The outlet from the pump was disconnected so someone tried messing with it at one point.
Hmm... looking back at this test run video with the old pump and feeding it from a funnel, I wonder how it worked at all. I mean, I did prime it by having the funnel above the pump before I stated it with starring fluid, but as you can see, it kept running well beyond when I had the funnel lower the pump. The fuel in the bowl should have run out by then, yet it was still running and the gas level in the funnel appears to be going down slowly. The pump might be weak though, hence the surging you see.
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I wonder if that destroyed rubber piece is just the anti-drain back valve? Maybe I don't even need a pump, just a 1/4 in-line check valve near the fuel tank. There is an o-ring in the pump though too, but that's pretty standard stuff. I can probably find one close enough to work there.
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This is worth investigating further. Next clear'ish day and when I feel like it, I'll stick my HFT fuel pressure test gauge on the output and feed it gas from a gas can. I just won't bother hooking it to the gen. fused 12v directly is all it needs.
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Even if it seems to pump, I'll probably just keep the new one and install it, and keep the old was an emergency spare that may or may not actually work in said emergency situation.
I have a tiny 500W Yamaha gen that i carry too for more daily uses, not to mention my 400W of solar on the roof, so the big gen is just a rare thing I run. But it's nice to have when I need it. It can run AC, the electric element on the water heater (also LP), an electric heater (such as the block heater!), microwave, etc. Just nice to have a ton of power handy, just in case.