| Onan Question [message #277888] |
Fri, 15 May 2015 17:34  |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Senior Member |
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All,
Finally got my Onan going and putting out voltage again thanks to Jim Miller and his rewound field winding! While I had it out for the winding replacement I also replaced the bell end bearing and de-carbon the heads and replaced the control board. Got it back in and it fired right up. After some carb adjustments (Main jet) I got it running as smooth as could be but only under a full load (roof air on). Voltage and Hz very steady. When there is no load on the Onan is not as smooth and voltage jumps around 3 to 4 volts. I tried adjusting the idle mix screw, which the MM says is for no-load adjustment, but the idle mix screw has no effect, meaning I can screw it all the way, no effect, screw it all the way out, no effect. I was thinking I must have a vacuum leak so I spayed carb cleaner on the intake and did find a leak between the carb and the intake manifold. Great, so I figured this is the problem. Replaced the gasket, ran again but still no joy. although slight better (no more vacuum leaks). After letting it warm up tried to adjust the idle mix screw again but still mix screw has no effect.
Any ideas as to why the idle mix screw is having no effect? Again under the load of the roof air the Onan is very smooth, voltage/Hz very steady.
Any advice would be greatly appreciated.
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: [GMCnet] Onan Question [message #277894 is a reply to message #277888] |
Fri, 15 May 2015 20:30  |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On May 15, 2015, at 6:34 PM, Jon Payne wrote:
> Any ideas as to why the idle mix screw is having no effect? Again under the load of the roof air the Onan is very smooth, voltage/Hz very steady.
Hi Jon,
Did you do any rebuild work on the carb while you had the rest of the unit apart?
--Jim "saving the lives of Onans...one unit at a time" Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Onan Question [message #277898 is a reply to message #277888] |
Fri, 15 May 2015 21:50 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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What I do is with no load on it manualy hold the throttle to an "idle" speed using the min speed screw as a stop setting to accompish this. Then adjust the idle mixture. Release the throttle and allow the governor to get to normal speed. Now readjust the high speed mix with no load. Reset voltage (speed) to 125 and test with load. You may have to adjust the gov sensitivity to get best steady speed. Reset voltage each time. The manual does not give much detail on carb adj and I don't see how the idle mix can have much effect at normal throttle though it may sum with the main jet JWID.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Onan Question [message #277902 is a reply to message #277894] |
Fri, 15 May 2015 22:17 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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The air passage to the idle screw is blocked/plugged with dirt. Carefully apply low pressure compressed air to the idle screw bore with the screw removed. Maybe do it inside a plastic bag so you can see if you clear anything out.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] Onan Question [message #277914 is a reply to message #277894] |
Sat, 16 May 2015 12:04 |
Jon payne
Messages: 495
Registered: May 2008
Karma: 1
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Senior Member |
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Jim,
Carb is a rebuilt one I got from Applied.
Again, runs very well overall, it does not hunt at all and runs perfect under load with the voltage and Hz steady at ~124VAC/60Hz. Mainly I'm curious to know why the idle mix screw has no effect. I don't suspect any dirt but would explain why the idle screw has not effect.
If I could mimic what is sounds like it would be like this (no load) "mmmmmmmmmmmmmmmbah..bah...bahmmmmmmmmmmmmbah..bahmmmmmmmm....bah...bah...bah....mmmmmm"
Thanks.
Jon
Jon Payne
76 Palm Beach
Westfield,IN
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| Re: Onan Question [message #277943 is a reply to message #277888] |
Sat, 16 May 2015 23:03 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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Jon Payne wrote on Fri, 15 May 2015 16:34All,
Finally got my Onan going and putting out voltage again thanks to Jim Miller and his rewound field winding! While I had it out for the winding replacement I also replaced the bell end bearing and de-carbon the heads and replaced the control board. Got it back in and it fired right up. After some carb adjustments (Main jet) I got it running as smooth as could be but only under a full load (roof air on). Voltage and Hz very steady. When there is no load on the Onan is not as smooth and voltage jumps around 3 to 4 volts. I tried adjusting the idle mix screw, which the MM says is for no-load adjustment, but the idle mix screw has no effect, meaning I can screw it all the way, no effect, screw it all the way out, no effect. I was thinking I must have a vacuum leak so I spayed carb cleaner on the intake and did find a leak between the carb and the intake manifold. Great, so I figured this is the problem. Replaced the gasket, ran again but still no joy. although slight better (no more vacuum leaks). After letting it warm up tried to adjust the idle mix screw again but still mix screw has no effect.
Any ideas as to why the idle mix screw is having no effect? Again under the load of the roof air the Onan is very smooth, voltage/Hz very steady.
Any advice would be greatly appreciated.
Jon
idle mixture screw has no effect on the running of the Onan in this application.--only the main jet affects what we need.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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