Onan Carburetor Blues! $$$$$$$$$$$$

[Wyatt]

Onan actually wants you to run the generator once a month for TWO hours with a 50% load.

They also have specific instructions for storing the unit and putting it out of and brining it back into service.

It’s the failure to exercise the generator once a month that will cause the surging as the carburetor fuel bowl will gum up as many have said.

The funny thing about these generators are if you rent an RV with a generator they don’t want you to run it for very many hours but the more you run it the better it is for the unit.

A couple of other tips that are in the manual. When checking oil level do not screw the dipstick back in. Just dip it back in.

The only thing that I vary from is they recommend changing the oil once a year or every 150 hours and I change mine every 50 hours. There’s no oil filter on these things and oil‘s pretty cheap compared to repairs.

[Kickenrock]

Originally Posted by DesertRatt

The gen starts right up, but only runs about 10-seconds. It races up to high rpm, then drifts down to try to idle, the goes up a few hundred rpm and shuts off.

If the "jet" was blocked, would it start?

Yes it could. The choke would make the initial start mixture rich, it would run until the choke opens and the mixture becomes too lean, it would slow to idle and then quit as you described.

[navnaz]

I was having intermittent starting problems ( the choke) with my Oman Cummings 5500. I bought one of those $50 replacement carbs after reading good reviews on them. I put it in after watching a YouTube.com video on how how to replace the carb. On the blog that reviewed the $50 carb included a RV repair shop that replaces carbs and swears by them. It took me 20 minutes to replace and it started first try. Now the generator starts beautifully every time we push the start button. I would buy another one.

[09 harley]

Originally Posted by Morich

While it is always popular to blame something on somebody they don't like, carb fouling blamed on ethanol is not very accurate as carb fouling has been around as long as carbs have been used!
We used to tear the old 53 Ford down every once in a while and clean the carb and that was way before ethanol in gasoline.

I’m very sorry if I offended you. I didn’t mean to suggest that the ethanol in the fuel causes all the problems in carburetors. All small engine manufacturers had to modify the construction so the seals and passages would perform as designed. The ethanol absorbs water and provides full time jobs for small engine mechanics. Stop by your local Honda shop and ask to speak to their service manager. He will be glad to explain this situation to you and explain the problems he sees every day. You might also go to a large store selling power equipment to the professional gardeners. They are backed up with this problem but they like the revenue. This problem is another example of unintended consequences. Have a great day.

[valsamik]

I had similar problems. I tried on of those so called replacement valves and they aren't worth it.

I took the disassembled carburetor and let it soak in Gunk Carb Parks Cleaner for 2-24 hour baths and used an air compressor to blow out the openings between baths.

Reinstalled the carbureator and was still a little rough. So I took so Seafoam and fuel mixture and clean out the system this way a couple of times and the generator came back to life...first starts every time now.

One additional thing I did was install an inline fuel shutoff-off valve, so I can prevent leaving fuel in the carbureator for long periods of time. I run the carb dry after my last use on a trip and has proven to work for the pas year without any additional hassles like I had before.

[Cr250]

DesertRatt, yes, it will start and act just as you described, the Pilot jet is plugged, so it's not getting the fuel on the idle side, the governor calls for more fuel, top end, then the main jet takes over. Hence the surging or hunting. I'm new to RVing but not to wrenching.

[DesertRatt]

Originally Posted by Cr250

I'm new to RVing but not to wrenching.

Clearly! Thank you. My project for next week when we get back.

[creativepart]

Originally Posted by Wyatt

There’s no oil filter on these things and oil‘s pretty cheap compared to repairs.

There most certainly is an oil filter on my 5500 Onan! I just changed it last week.

Some smaller output models don’t have an oil filter but the 5500 and larger most definitely do have one.

[al1florida]

Originally Posted by 09 harley

The solution is to prevent the problem in the first place. The problem is the ethanol in the fuel. The solution is to purchase non ethanol fuel. They are not hard to find. Buy 5 gallons at a time and you should be able to find it during your travels. I use it for all yard, garden, and any small engine I have and I have never had a carburetor related problem. You can thank our leaders for this crazy idea.

I believe the Onan generator the OP has is built into the RV and takes its fuel from the same tank the motorhome engine uses. Makes it much more expensive to run non-ethanol fuel, not to mention most gas stations I visit in my travels don't have non-ethanol fuel.

[DesertRatt]

Where I live in Cali, no one seems ethanol gas.

[Wyatt]

Originally Posted by creativepart

There most certainly is an oil filter on my 5500 Onan! I just changed it last week.

Some smaller output models don’t have an oil filter but the 5500 and larger most definitely do have one.

Well, to be concise then, not on my 4000...

Not sure which model the OP has, as I didn’t see that in his post. I can only comment on what I know, if I’m going to offer some advice. Mine doesn’t. I don’t know if his does, or not...

[DesertRatt]

No oil filter on mine.

[Smittty54]

I had a very rough running staling Oman generator. I looked on YouTube and followed the directions about pulling the gas line and sticking it in a jug of gas/sea foam. I did it twice. Than changed the fuel filter, air filter, oil and filter. Now it runs like a champ . I now exercise it every month without fail. If I were you I would try the sea foam 2-3 times if necessary before you give up. It is not difficult. This also worked on an old lawnmower and weed eater that had not been run in 2 years.