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Onan Generators Restoring, operating and maintaining vintage Onan generators. When asking new questions about your generator, ALWAYS give your model number AND serial number.

Onan Generators

It's alive, again!

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Old 09-04-2009, 10:05:15 AM
robinpaillot robinpaillot is offline
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Thumbs up It's alive, again!

ONAN generator [4.0BGE-1R/26101C] OK, so another development. Everything was OK until yesterday. Still needed to adjust the carb [I had already taken it apart and cleaned it], generator is running rich, choke was wide open. However I was going to wait a few weeks before messing with it.
I went to exercise the set and the dreaded 'stop when start button released' problem arose. So back to the drawing board.
Grounded the oil pressure wire from the control board, no luck. Also tried leaving it ungrounded ,still no love. Checked for AC voltage by putting a meter on the choke and am getting 20VAC like the manual says. Checked R6, charging resistor, and got 2.9 ohms. Checked voltage at breaker, 134VAC. A little high but close to the range, 127VAC +- 4.5 V. Pin 5 goes to resistor R7, which I can't find on the schematic. R7 looks a little burned and is getting hot when running. Pulls 3.5 amps @ 17.5VAC. Voltage drops to 3.5 on other side of resistor. Probably from running in 'start' mode. Checked voltage at the B+ side of solenoid: 12.5VDC before cranking, 11.4VDC when running [with start switch held in on all above checks].
Then I remembered something that BTPoster [Bruce?] said in one of his posts. Something about not being rocket science, just basic DC wiring [thanks for the reminder]. Without voltage to the ignition coil, the motor won't run. With voltage getting to the circuit board when running with start switch held in, what causes the voltage loss to ignition coil when switch released? Reading the operation chart I found that the K2 relay energizes the K3 relay for running. I'm sure there's a good reason for a relay to control a relay to control a relay etc. I don't know, I'm just a mere mortal. Checked the K2 relay with meter. Continuity for relay coil, 1to4. No continuity from 5to3 resting position or 5to2 when energized with an external battery. Cut open the relay to check the contact points, they were good. Found that point 5 was broken between the relay and the wire sticking out of the circuit board. Desoldered the wire sticking up, filled hole with solder and another piece of wire, checked continuity, all good. Plug everything in and she starts and runs when start switch released, 116.4VAC at an outlet inside! It even started from the remote switch inside the rv. Made a new cover for the relay from a piece of plastic and some heat to shape and 'weld' the seams. At some point I'll find another K2 relay or a dead board [with a good K2 type relay] that someone will sell me real cheap. [300-2784/2943 Control Board]
Decided to adjust carb while letting the generator run. The motor was running rich and 'puttering'.The main jet seemed to be out by about 2.5 turns, manual says 1.25. When I turned it in it seemed to run better. Kept turning until the motor smoothed out. However when I turned the a/c on in the rv, the generator died. Turned the a/c off and the generator started right back up. I guess I should have turned the idle adjust instead of the main adjust. Will do that next time I work on it.
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Old 09-04-2009, 10:35:18 AM
Ted_Cool Ted_Cool is offline
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Default Re: It's alive, again!

I've been wondering if the idle circuit plays much of a role, as it starts with the throttle wide open, then runs at 1800 thereafter. Not much idling going on there...

I would set the idle jet to spec by counting turns, and fool with the main jet from there.

A vacuum gauge is probably your best bet for tuning, if you can find a place to connect it. I had to remove my manifold and drill and tap the boss to get a useful port on my JC set.
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Old 09-04-2009, 11:32:26 AM
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Elden DuRand Elden DuRand is offline
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Default Re: It's alive, again!


It could be that you leaned out the high speed adjustment too much and the engine "leaned-out" when the throttle opened to make the engine take the added load.

The way I adjusted mine was to run it until it warmed up then, with no load, very slowly turn the high speed adjustment closed (clockwise) until the engine just starts to falter then open it (counterclockwise) about a quarter turn.

Now, to check the adjustment, shove the throttle to the idle position (which should be just a little shy of governor speed (say, 1,500 RPM for a 60 cycle unit).

Once the engine had settled down to that speed, quickly release the throttle shaft and see if the engine picks up speed smoothly. If it stutters a bit, turn the high speed adjustment slightly counterclockwise and try it again.

The "sweet spot" is where it just picks up smoothly when at operating temperature.

Now, when the engine is cold, it might be a bit cranky about taking a load but, since it is supposed to be up to temperature when handling a load, let it warm up and it'll be okay.

At least that's the way I do it.

Take care - Elden
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