Onan 4000 won't "idle"

[thesameguy]

I have an Onan 4BGEFA26100K and, I have to admit, I've been negligent in its maintenance. I just don't use it that often, which, I suppose, is part of the problem.

After the smog shop crashed my motorhome into their garage, I was unable to start the generator to test the AC. I assumed it was something simple, but it's not. The generator is very slow to start - it cranks readily, but takes probably a minute and a half of cranking in total - I usually crank it for 10-15 seconds, let it rest a bit, repeat, to prevent the starter from dying. Once started, it won't idle - it revs up and down pretty much in perpetuity. Stopping and restarting changed nothing - still a bouncing idle. It used to take 45-60 seconds total cranking, and would idle instantly, always.

The autochoke is causing the problem - the actuator bounces back and forth, back and forth. On Saturday, I adjusted the idle stop screw to a point where the idle fluctuation was somewhere between minimal and nil and ran it for 5-10 minutes. I did not put a timing light on it to see how fast it's running, but that's neither here nor there.

As I mentioned, I did this to myself. It has not been touched in two years (!!!) which was obviously a mistake. I have a bunch of supplies coming for it - oil change, fuel filter, air filter, and spark plugs. I don't expect any of these will cure it, but I'm hopeful. I have no maintenance history on it whatsoever, I know only that it worked. Beyond the things I've mentioned, is there anything else anyone recommends looking at to a) help it start easier, and b) fix the idle situation? Since purchase, I've been considering a new fuel pump as I don't think even 60 seconds of cranking is normal, but perhaps that's related to a greater issue, perhaps with the carb?

Any thoughts are appreciated!

 

[sadixon49]

Lord knows we all wish to be self sufficient, and I sure would hate to have to pay to repair something which I felt I could fix, but there comes a time, and you're quickly approaching it, when a trip to an approved Onan/Cummins tech is in order.

 

[thesameguy]

There is no magic in this technology. That genie has been out of the bottle for a long time! I was hoping someone here would have some advice, but if push comes to shove I'll buy the manual. Whatever the issue is, it's just not that complicated. I'm just not sufficiently knowledgeable about the pieces in play to create a theory.

 

[jluke]

Sounds a bit what my Generator was doing, for the same reason. I took off the carb, removed the bowl which was full of gunk from the gasoline evaporating, then sprayed carb cleaner through every orifice I could. Reinstalled and it's run fine since, costs nothing and worth a try. When these aren't run, the gasoline evaporates and leaves behind varnish and tars that clog up the works. Good luck. You should also add some Stabil to the gas in the tank if it's going to sit for a couple of months.

 

[Arch Hoagland]

Once or twice a year I put five cans of Seafoam in my 75 gallon gas tank before a long trip. During that trip I make sure to run my Onan 5500 generator for at least an hour.

Today's gasoline goes bad in a few months and if you aren't running the generator regularly you will have problems, guaranteed.

I think I'd run some Seafoam through it first and see what happens.

 

[APRSRVer]

I wouldn't rule out a fuel problem. As has been pointed out, fuel in the supply line and carb bowl will go stale and cause erratic idling. Has the fuel filter been change? Also, the fuel line from the tank to the generator can deteriorate. It can collapse and/or develop an air leak. I've had to replace mine due to hard starting and I discovered the problem while doing so.

 

[GnS]

Agree with the carb being gunked up. An air leak is also a possibility as was stated above. Seafoam is good stuff and I use it on every gas burning engine I own.

 

[thesameguy]

I wouldn't rule out a fuel problem. As has been pointed out, fuel in the supply line and carb bowl will go stale and cause erratic idling. Has the fuel filter been change? Also, the fuel line from the tank to the generator can deteriorate. It can collapse and/or develop an air leak. I've had to replace mine due to hard starting and I discovered the problem while doing so.

It shouldn't be a fuel problem - the motorhome hasn't been unused, just the generator. We haven't needed it the last few trips. Gunk in the carb is definitely a consideration, however - if the tuneup doesn't help, I will remove it and give it a good cleaning. I'm pretty sure I need to remove the generator to replace the second spark plug, so that will give a good opportunity to check out the carb and any vacuum lines. The ones I have access to seem good - not soft or hard, no cracks, etc. The fuel line itself - from tank to generator - was replaced. It was in poor shape when I bought the motorhome and I replaced it before my first outing.

 

[ironrat]

My unit acted about how you describe. Yes clean the carb bowl for sure. What I needed to do on mine was to prime the fuel system before starting, once I started doing that no problems. Too do this you hold the stop button in till you see the run light, hold it for about fifteen seconds then start her up, worked for me.

 

[driftless shifter]

The main engine and the generator only share the fuel tank. All the fresh gas used by the main engine goes through on fuel system and all the gas for the generator sat in its separate fuel system for an indeterminate amount of time going sour. The generator starts and runs, I would add a very strong dose of SeaFoam or Techron fuel system cleaner to the gas tank and let the generator run for hours and maybe more hours. You may get lucky and it will clear up over time as the cleaner circulates through the entire system.
By the way, the symptom you describe is called surging and is a classic sign of a fuel delivery problem.

Bill

 

[thesameguy]

Sure, but the line between the tank and the generator is only a few feet long, maybe six or eight. There just isn't *that* much fuel in there. After running for 20-30 minutes that fuel should be all fresh.

In any case, I'm not sure if you all heard it last night, but that sound around 8pm Pacific was me screaming and trying desperately to kick my own ass. I changed the oil in the generator - the oil filter was dated 22 July 2009. Oh man. Not good. Seriously never even occurred to me to do my normal "new used car tuneup" on the generator. Lesson learned.

Conveniently, the Onan generator uses the exact same size filter as my lawn mower and my Saab and my Alfa, so that's nice. New oil filter, new Castrol oil, and the bloody thing started right up. Like, almost instantly. I suspect either the filter was so clogged or the oil so old that there wasn't enough pressure to keep the fuel system running once the starter was released. After a while, pressure built up and it'd kick in. I can get behind that.

It still will not idle properly. I can watch the autochoke go full open when the generator off or starting, then full closed the second it starts running, then full open to catch itself, then full closed to slow itself back down, forever and ever.

As I mentioned, I adjusted the throttle stop screw to almost maximum, and in this position the generator now starts easily and will run indefinitely at a fixed speed. If I back off the stop screw, it goes back to its open-closed cycle. It seems that whatever mechanism adjusts throttle position has lost all control of the middle part, BUT it could be that other components - fuel or ignition - aren't doing their job adequately at low engine speeds.

In any case, I ran it for 20-30 minutes last night without incident, so now I'm waiting on the rest of my tuneup stuff to see if that helps any. If not, I guess I need to learn how the autochoke works - it can't be that tough. Maybe I'll go ahead with a fuel pump. It's old, replacements are cheap. Plus Seafoam. That's solid advice!

 

[GnS]

The idle speed fluctuation is often a problem in the float bowl. Look for a partially clogged fuel inlet. A shot of carb cleaner through the straw from the float boss side will usually clear it out. Make sure the idle fuel jet is clear of gunk also.

The fuel they sell nowadays can turn to a gel in about 30 days or so... been there, done that with my Harley carb and a few lawn mowers.

 

[john owens]

Float bowl is full of gunk...happened to mine. I just tapped on the bowl with a wodden handel and it runs sweet..but still tune it up. And exercise that baby every month at least for an hour!!!!!!!

 

[thesameguy]

Good deal, and will do! It looks like the carb has to come off to gain access to any discrete parts - not a lot of clearance in the compartment. Anyone happen to know offhand a part number for the gasket set? I'm sure Napa has it, but it seems there were a lot of versions of this general class of generator and I don't want to end up with the wrong parts.

Edit: Or maybe I should just pony up for the manual.. can't be that expensive. I found links to PDF versions on Cummins site, but they're apparently long dead.

 

[john owens]

Check with your RV dealer or some outfit nearby. Most competent RV shops also are certified to work on Onan gensets. They should be able to supply/mail the needed parts.

 

[Arch Hoagland]

This link works today:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiI6N7RyorKAhUJKWMKHUAyBvEQFggcMAA&url=http%3A%2F%2Fpower.cummins.com%2Fsites%2Fdefault%2Ffiles%2Fliterature%2Frv%2FF-1123-EN.pdf&usg=AFQjCNGikJOhbFooDaUre8Fgk434eOTeSw&sig2=PH8boLgZNySUQl9qSilTHA&bvm=bv.110151844,d.cGc


Wouldn't work the other day when I posted.

I'd be curious to know what you find out when you change the parts.

 

[thesameguy]

I appreciate the link (it does work!) but those are all much, much newer than what I've got. I believe mine is an Emerald I 4000 - c1993!

 

[Busskipper]

Sounds a bit what my Generator was doing, for the same reason. I took off the carb, removed the bowl which was full of gunk from the gasoline evaporating, then sprayed carb cleaner through every orifice I could. Reinstalled and it's run fine since, costs nothing and worth a try. When these aren't run, the gasoline evaporates and leaves behind varnish and tars that clog up the works. Good luck. You should also add some Stabil to the gas in the tank if it's going to sit for a couple of months.

Sort of sums it up - basically just fuel and spark to make it run, so Clean the source of the fuel if it has been sitting, and I suggest (Often to my own neglect) to shut off the fuel and run the carb dry, then the varnish will not mess up the carb, This is much more prevalent now with the Bio Fuels that are mandated in Automobiles gas pumps.

BOL,

 

[thesameguy]

Got my hands of the service manually, and I think it's good to go. There was minimal gunk in the bowl but the filter was highly obstructed. With a clean bowl, new oil/fuel/air filters and fresh plugs and an oil change it seems fine. Starts up after about 12 seconds and sets into a nice idle. I ran it for about an hour today in three separate sessions and each time it started and idled without incident. Wish I was able to test it with load like the AC, but that's obviously an entire different problem.

 

[driftless shifter]

Put a space heater on it, set it on high, run a blow dryer, make a pot of coffee, use the microwave. Any of these will put approximately 1500 watts load on the genny.

Bill