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Onan Generators

What Have You Done to Your Onan Generator Today?


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  #1911  
Old 10-21-2015, 09:11:01 PM
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Default Re: What have you done to your Onan generator today?

Leon, you do realize there is both a 'main' and 'idle' mixture adjustment screw on the gaseous carb, right? Have you tried opening the 'idle' screw? (It's not very sensitive - I think you might be surprised how much you have to turn it to see ANY difference...) I found that helped the NL instability quite a bit on one of my gaseous-fueled JB sets.
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Old 10-21-2015, 09:47:03 PM
Leon N. Leon N. is online now
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Default Re: What have you done to your Onan generator today?

Jim, yes I am aware of the idle mixture screw. It is not a big player in this. BTW, the JB ran perfectly today, no hunting and it stayed in spec. I was surprised. Also, it was much much warmer than before when I had the speed variations. I prefer to exercise the plant more rigorously in cold weather. It is cheaper for us to power our electric dryer from the JB than to buy KWH from National Grid.

I remain surprised and curious why when running at NL it would sometimes start hunting and popping through the carburetor and then just as quickly smooth out and purr like a kitten. The Garretson was cold soaked at around freezing temperatures at that time.

Now today temps were in the 50's and the JB ran perfectly.
I
One other observation that makes me think it is the NG regulator. That is when all this was happening on the colder day, when the JB did settle down, if I tweeted the throttle with my finger, it went crazy. Today, when I tried the same thing, nothing happened and the JB did not hunt like on the colder days run. Also, today, I could make it hunt by blowing into the Garretson vent port. Presumably, I was forcing more fuel in and it did not like that.

Guess I will wait for a colder day and try heating the Garretson to see if that helps per Len k's suggestion.
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  #1913  
Old 10-21-2015, 11:19:25 PM
len k len k is offline
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Default Re: What have you done to your Onan generator today?

Idle mix screw usually wants to be adjusted at idle rpm (~600 ?) for best running, on gasoline anyways. (disconnect magnaciter).
Main mix screw is usually adjusted at full load for best running. Turn both ways till it bogs a bit then put it 1/2 way between.
Adjust min RPM idle stop screw as per manual, sometimes it's set to a rpm , sometimes X turns from a certain idle rpm.

Last edited by len k; 10-21-2015 at 11:33:50 PM.
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  #1914  
Old 10-22-2015, 11:01:21 AM
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Default Re: What have you done to your Onan generator today?

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Originally Posted by Jim McIntyre View Post
Leon, you do realize there is both a 'main' and 'idle' mixture adjustment screw on the gaseous carb, right? Have you tried opening the 'idle' screw? (It's not very sensitive - I think you might be surprised how much you have to turn it to see ANY difference...) I found that helped the NL instability quite a bit on one of my gaseous-fueled JB sets.
Here is the settings on my idle and main fuel mix for my 7.5JB and yes I know every Carb setting on these JB ,s may differ to wear on the idle and main screw seats or needle just FYI mine is set idle screw out 2/1/4 turns and main fuel mix 3/1/4 turns and that is tweaked settings starts and runs good for now . Leon what ever is making your JB act that way could not be nothing serious maybe it just needs a nice work out for a couple of hours I have found out over the years anything that just sets around will end up with some sort of issue an automobile everything drys up me I run better after I am up for two hours every morning this is just my 2 cents
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Old 10-22-2015, 02:07:09 PM
Leon N. Leon N. is online now
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Default Re: What have you done to your Onan generator today?

Onan Dan I agree with your comment about the JB needing a nice work out. I am waiting for another cold snap to see if I can pin point my problem to that 50 year old Garretson Regulator. I am confident the gas pressure coming into the regulator is constant and I suspect it is not responding correctly to the JB demands perhaps due to cold temperatures.

For example, on a cold day I can make the JB hunt merely by touching the throttle. I suspect any throttle changes affect the demand suction from the regulator and it does not respond correctly. Maybe letting too much gas and that causes the hunting condition. I can do the same by tweaking the main mixture screw CCW just about a half turn. More later.
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Old 10-23-2015, 01:05:55 AM
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Default Re: What have you done to your Onan generator today?

I have seen demand regulators full of thick oil goo from LP gas which sticks when cold
Just a thought

Butch
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Old 10-23-2015, 08:12:15 AM
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Default Re: What have you done to your Onan generator today?

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Originally Posted by len k View Post
Idle mix screw usually wants to be adjusted at idle rpm (~600 ?) for best running, on gasoline anyways.....
But since a generator engine NEVER idles, that's not the optimum way to adjust the idle screw on a generator.
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Old 10-23-2015, 09:55:46 AM
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Default Re: What have you done to your Onan generator today?

Most of the manuals will show how to adjust the carb and governor on the onans on the idle most show that when the governor is held against the idle stop by hand the onan should idle like 95 to 100 volts on the volt meter or kill-o-watt meter use the meter to adjust the idle adjustment under no load and to adjust it turn to out to richen and in to make it leaner then find the happy medium setting adjust half way between leaner and richer and then re check the idle voltage by holding the governor against the idle stop by hand and reset if changed to 95 to 100 volts screw in the little screw on the idle stop or un screw until it reads 95 to 100v
The main fuel adjustment manual says to set it under full load leaner or richer by watching the volt meter or kill-o-watt meter to get the best out put AC volt not to rich or not to lean . the manual; will show where to start with the adjustment settings on a carb to get the onan to start and then start the adjusting once the onan has ran and warmed up a while also one wants to be sure the automatic chock is working properly then to one has to be sure the governor is set correctly so that is the way I set my onans.
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Old 10-23-2015, 10:26:13 AM
len k len k is offline
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Default Re: What have you done to your Onan generator today?

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Originally Posted by Jim McIntyre View Post
But since a generator engine NEVER idles, that's not the optimum way to adjust the idle screw on a generator.
True never idles, but air flow thru carb does vary greatly from no-load to full load as throttle changes position. I would think you would still want to adjust carb the normal way so air/fuel mix is still correct over the full range of throttle positions the gen will see.

I read in NHE type service manual about adjusting gasoline carb this way, haven't read JB manual. What is the optimum way for a JB?

I believe idle stop rpm screw is to set min rpm so gen doesn't stall out after load dump, when gov commands zero engine power for a second or so. This is also the time carb will likely be operating only on the idle jet, so you got to set it right.

Last edited by len k; 10-23-2015 at 10:38:07 AM.
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  #1920  
Old 10-23-2015, 01:31:51 PM
Leon N. Leon N. is online now
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Default Re: What have you done to your Onan generator today?

Onan Dan re your comment:"---Most of the manuals will show how to adjust the carb and governor on the onans on the idle most show that when the governor is held against the idle stop ---".

Don't try this if your machine is equipped with a magneciter back end.

You say most manuals? Hmm! Certainly not in my Onan Operators manual. In fact my manual talks about adjusting the gasoline idle mixture adjustment at no load and factory carburetor adjustments should not be disturbed. The gasoline idle mixture screw should be adjusted at 1800 RPM, with no load applied and use a tach or frequency meter, not a voltmeter.
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