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 > How perfectly should my Onan run?

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j-d

Sunny Florida USA

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Posted: 07/12/18 06:06am Link  |  Quote  |  Print  |  Notify Moderator

From what I remember from the ONAN Manual, the Voltages and Frequencies you state, are within "normal." How much fluctuation within those ranges is another matter. To a degree, they'll "hunt" for the right throttle position to stay in range when the load changes. Definitely shouldn't "surge" over a wider range, particularly at idle. Remember, "idle" is still 3600 RPM. It's running at that RPM under no load and therefore a different throttle position and different carb passages than at full load.

Ours definitely reacts when A/C kicks on/off, microwave the same, I don't notice it on smaller loads like coffee maker. It probably DOES react, just not noticeable. Is yours disturbing, or something you've gotten interested in, and sit there monitoring?

I mentioned different carb passages. According to an ONAN tech a few years ago, the 4KY carb has a square internal corner in the idle circuit. Very hard to clean. You can try what some of us have done successfully: Make up a tempory "tank" with a gallon or two of gas that's VERY rich with your Berryman. Connect that to the genny and let'er run. Shut off and allow the rich Berryman to soak in. Run again. Do this over a couple days. Just "might" get the last of the goo out.

Many of us put Stabilizer in EVERY DROP of gas that goes into the main RV tank that also feeds the generator. I'm one of those guys, haven't had trouble since I lucked into a clean used carb off a junked 4KY. Stabil is the one everybody thinks of, but Startron works at a fraction of the price. Big bottle from Amazon.

With an old ONAN BFA, I had the carb cleaned and rebuilt by a fuel system shop. Ran FAR better than before but still had a "surge" and a new Governor Spring solved it. A few dollars very well spent.

See what the ONAN guys say when you're there for a new Spring. If Spring doesn't help, try Berryman.


If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB

Straylight

The Road

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Posted: 07/12/18 08:26am Link  |  Quote  |  Print  |  Notify Moderator

K Charles wrote:

The OP says he has not removed or adjusted the idle screw and the "main carb adjust" is screwed in as far as it will go. How did the OP clean the idle screw if he never took it out. I would first adjust the idle and main jet.

Correct, one of my worries is that the idle screw area in there is particularly bad; I couldn't get at it with my can of Birkebile and I of course can't determine what effect the ultrasonic cleaning had on it. Note that I cannot adjust the idle screw: There's a metal plug on top of it.

Thanks for all the other comments. I think I'll have my Onan guys put in for a new governor spring and a new governor linkage spring, see if I can spend twenty bucks instead of two hundred on a carb. I'm sort of resined (get it? because of the sinusoidal surging...) to the new carb, though.

Another symptom popped up: I had adjusted all of the screws when the genset was nice and hot. I would describe it as running "acceptably" (not immaculately, per the comment about the tooth fairy above). Later, after it cooled, I went back and turned it on and the surging was very bad again.

Is that an important detail? Is there a failure point that would change depending on the temperature of the generator?

Straylight

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Posted: 07/12/18 08:32am Link  |  Quote  |  Print  |  Notify Moderator

Double post: ...can I just pull that tamper proof plug off the idle screw? With a metal pick or something?

j-d

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Posted: 07/12/18 08:36am Link  |  Quote  |  Print  |  Notify Moderator

Straylight wrote:

...I cannot adjust the idle screw: There's a metal plug on top of it...
...new governor spring and a new governor linkage spring, see if I can spend twenty bucks instead of two hundred on a carb...
...Is there a failure point that would change depending on the temperature of the generator?


Metal plug is an indicator of the problem with the ONAN carbs. Sealed up to be non-tinkerable. That said, that 90* "corner" one of the techs told me about is probably adjacent to the screw you can't get to.

Governor Spring simply can't hurt. There's also a tiny spring or two designed to keep any lost motion out of the linkages on top of the carb (throttle and/or choke) so I'd guess it'd run sloppily if one was missing or disconnected.

Well, it has an automatic choke (thermostatic coil) to richen it for starting and warmup. So sure, Mixture does change with outdoor temperature and probably the operating temperature of your genny.

azrving

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Posted: 07/12/18 09:30am Link  |  Quote  |  Print  |  Notify Moderator

Drill a very small hole in the plug then gently insert a small screw and use pliers to pull the plug

wa8yxm

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Posted: 07/12/18 10:07am Link  |  Quote  |  Print  |  Notify Moderator

Continous surging (Hunting it is called) indicates an improper fuel/air ratio. I believe that is too rich. Stuck choke, or mal-adjusted carb are the most likely causes.

IT should be fairly Hz will wiggle a bit when a BIG load (A/C. Water heater. Microvave) kicks in/out but overall should be very stable.. "Purr like a kitten" is the applicable phrase if it's running right. A fairly big kitten.


Home is where I park it.
Kenwood TS-2000 housed in a 2005 Damon Intruder 377


azrving

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Posted: 07/12/18 10:11am Link  |  Quote  |  Print  |  Notify Moderator

Read the plug.....

maillemaker

office

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Posted: 07/12/18 11:18am Link  |  Quote  |  Print  |  Notify Moderator

Quote:

Tried everything to clean my carb. Took it totally apart, carb cleaner, compressed air and nothing worked.


From what I have read, cleaning solutions and even compressed air are unlikely to unclog the tiny clogged passages. You have to get a fine copper wire and thread it through the ports to clean them without damaging them.

Once the jets/passages are plugged only mechanical action seems to be the sure-fire way to clean them out. But you have to be very careful as it is evidently easy to wallow out the hole.

Steve


1990 Winnebago Warrior. "She may not look like much but she's got it where it counts!"



bounder39zman

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Posted: 07/12/18 02:49pm Link  |  Quote  |  Print  |  Notify Moderator

have cleaned/overhauled hundreds of these "tamper-proof" carbs, with
about 50% success rate. Very difficult to restore to perfect running condition, and getting balance on governor speed, sensitivity, idle, etc is a real art. Surging is usually air mixture problem, and "hunting" is a governor issue, but symptoms are similiar. The altitude compensating screw is the main mixture screw, you can pry the cap off carefully, dont bend the screw. When these units are running right, you should see a few speed fluctuations when load changes, but should steady out. Voltage will vary slightly, but should stay 115-125. A new carb would probably provide smoother operation, but sounds like it is acceptable the way it is.

Chum lee

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Posted: 07/12/18 04:04pm Link  |  Quote  |  Print  |  Notify Moderator

I don't mean to be a smart *ss but are you having any problems running equipment with the genny? Any problems starting it, reaching maximum output, excess fuel/oil consumption, exhaust smoke, overheating, noise, spark plug fouling, etc? I have the same unit and I can't hear yours, but, mine does change speeds/voltage slightly depending on load, altitude, temperature, etc. It has never failed to do what I ask it to do. Years ago I learned not to try to fix problems I don't have and I spend my time resolving the ones I do. Could you be expecting too much? Just asking. You have a very popular genny. It might be worthwhile to listen to others and see what they sound like before you condemn yours.

Chum lee

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