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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan JC Stumper


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  #41  
Old 10-06-2017, 10:24:45 AM
captainjdog captainjdog is offline
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Default Re: Onan JC Stumper

Thanks BigBlockChev,

Also, thanks for the reminder that I can use Hz to verify engine speed. Unfortunately, I was stuck on staring at the tachometer. I was going to verify 60Hz just to verify it, but forgot it is directly related to RPM. Going to verify 60hz / 240vac and then load test. From what I could dig up, the ceramic resister should tolerate at a minimum 300 degrees F, maybe more depending on what they are made of. I'll keep an eye on it and see what it stabilizes at.

Thanks again.
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  #42  
Old 10-07-2017, 02:58:12 PM
captainjdog captainjdog is offline
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Default Re: Onan JC Stumper

Ok,
Almost there, My cheap volt meter didn't measure Hz but the new tachometer is spot on. Generator is steady between 1796-1805 rpm. 242vac.

Let the generator run for about 30 minutes.
Ceramic Resister: 350 degrees F. Didn't get any hotter than that.
Cylinder Temp 240 Degrees F

Here is where I ran into a slight problem.
Load Testing:
Light load. When turning on lights and fridge the rpm dropped but slowly recovered (10 seconds) back to 1800. Held steady for about 15 minutes. Temps Stable.

Then, I tried a Higher Load (Oven only) the RPM would drop to about 1740. I adjusted the governor (flywheel side nut) to compensate back to 1800, but when I removed the high load, the RPM was too high, around 1860 and turning the (high speed) left screw on the carb counter clockwise,wouldn't bring the rpm back down. I tried adjusting the fuel mixture thinking perhaps it might be lean but the big mixture screw on the carb had no effect.

My original adjustment was I lowered the (high speed) carb screw counter clockwise until the screw had no effect lowering the rpm meaning the governor took over. Then turned the governor clockwise to bring the rpm up to 1800. Then I turned the carb screw clockwise until the rpm rose, then I backed it off 1/4 turn. So I thought 100% of the rpm control is now on the governor. Am I going about this wrong?

Thanks for everything so far

V/R,
Justin
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  #43  
Old 10-07-2017, 03:25:58 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan JC Stumper

There was a recent JB thread on here, very long thread. LOL I think it ended up the vent was plugged/restricted on the demand regulator, you might check yours.

I know you have had this unit for a while but I will ask, your idle speed set screw isn't screwed in too far is it? I do not recall there being a high speed set screw on the carb. and do not know what it's purpose would be?

I didn't reread all you posts, is this a vapor only carb. or a Tri-Fuel carb?

I have done the idle speed screw set too high and had issues with the governor working correctly!!! ; ^ (

Last edited by nothingbutdarts; 10-07-2017 at 03:28:14 PM. Reason: added info.
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  #44  
Old 10-10-2017, 10:29:02 AM
captainjdog captainjdog is offline
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Default Re: Onan JC Stumper

Nothingbutdarts,
I'm not 100% sure but pretty sure it has a Tri-Fuel carb. It has the gas bowl on the bottom, and the inlet pipe on the side for vapor. It also has a new regulator. Sorry I was using the wrong screw terminology. I was adjusting the Idle speed. I forgot the generator acutally idles at 1800 rpm.
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