Onan Generator Over Fueling Issue

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The choke plate closes when cranking and as soon as it starts the plate opens allowing air in. I picked up a pressure gauge for the fuel but ended up breaking my wrist the same day and haven't been able to do much with one hand. Once I get the fuel pressure verified, I'll have to go from there. I do have the manual now, just haven't invested much time towards it lately...
 
My 4000 has a mechanical choke when at ambient, the choke plate should be closed from a thermal spring which as it warms up, it opens up the plate.
Mine would also "open" when the unit cooled down, so I have learned to 'release' the stuck choke before starting, otherwise I would need to crank the unit for 'sometime' before it would fire up.
 

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My 4000 has a mechanical choke when at ambient, the choke plate should be closed from a thermal spring which as it warms up, it opens up the plate.
Mine would also "open" when the unit cooled down, so I have learned to 'release' the stuck choke before starting, otherwise I would need to crank the unit for 'sometime' before it would fire up.
OK, I'll definitely keep an eye out for that next time I'm cranking it. I've never payed any attention to see if mine stays open when cooling or not. It cranks right up with a fresh plug. It just doesn't stay happy very long. Maybe 20 minutes before it sputters out.
 
OK, I'll definitely keep an eye out for that next time I'm cranking it. I've never payed any attention to see if mine stays open when cooling or not. It cranks right up with a fresh plug. It just doesn't stay happy very long. Maybe 20 minutes before it sputters out.
A stuck closed choke is somewhat common on Onans. It has happened to my Onan. It was the first thing I checked when I once had your symptoms of running way too rich.

You should be able to force it open by hand after the genny starts and runs for a half minute or so and see if that fixes it temporally and then go for a permanent fix. Be sure to check the cheap tubing piece that transfers the heat from the exhaust to the choke:

1713401688464.png

-Don- Reno, NV
 
OK, I'll definitely keep an eye out for that next time I'm cranking it. I've never payed any attention to see if mine stays open when cooling or not. It cranks right up with a fresh plug. It just doesn't stay happy very long. Maybe 20 minutes before it sputters out.
If yours is flooding, it possibly could stay "closed" when warming up, that would definitely cause it to quit. I posted the image of an older Onan, I dunno if new ones still have the mechanical-style of choke.
 
OK, I'll definitely keep an eye out for that next time I'm cranking it. I've never payed any attention to see if mine stays open when cooling or not. It cranks right up with a fresh plug. It just doesn't stay happy very long. Maybe 20 minutes before it sputters out.
The tubing I showed in message 45 is shown at the extreme right on message number 43 when the photo is opened up and much larger.

That tubing is VERY important to turn off the choke and fails often. Before you even start the genny next time, check that tube when the genny is COLD. Make sure it has no tears, holes and is in both slots. It is connected from the bottom of the choke box to the exhaust. Without that heat from the exhaust on the coke coil, the genny will run VERY rich when it warms up and then will die.

And it's such a common failure, buy a spare. You can get them on E-bay here.

-Don- Reno, NV
 
Choke adjustment: Onan manual (8-17)

1. Allow the genset to cool down. The tempera-
ture inside the housing must be the same as
the ambient temperature.

2. Loosen the adjustment screw holding the ad-
justment plate.

3. Slowly rotate the adjustment plate until the bi-
metal choke shaft connection is visible in the
sight window. This is the correct setting for an
ambient temperature of 70° F (21° C).

If the ambient temperature is higher or lower
than 70° F (21° C), make a mark on the choke
coil housing opposite the center mark on the
adjustment plate. Each mark on the adjustment
plate is equal to 10° F (12.2° C) of difference
from 70° F (21° C). If it is warmer than 70° F (21°
C), rotate the plate clockwise. If the tempera-
ture is less than 70° F (21° C), rotate the plate
counterclockwise. Tighten the adjustment
screw.

Example: If the ambient temperature is 90° F
(32° C), rotate the adjustment plate two marks
clockwise from the 70° F (21° C) position
marked on the housing.

4. Move the choke lever back and forth to check
for free movement. Verify that the choke does
not bind or stick.
 
A stuck closed choke is somewhat common on Onans. It has happened to my Onan. It was the first thing I checked when I once had your symptoms of running way too rich.

You should be able to force it open by hand after the genny starts and runs for a half minute or so and see if that fixes it temporally and then go for a permanent fix. Be sure to check the cheap tubing piece that transfers the heat from the exhaust to the choke:

View attachment 172392

-Don- Reno, NV
The choke does open right after starting. It is open before cranking, closes while cranking, and then opens after start up. This seems to be proper function to me. I will go over the parts for the choke assembly just to be sure there isn't any gremlins hiding there.
 
If yours is flooding, it possibly could stay "closed" when warming up, that would definitely cause it to quit. I posted the image of an older Onan, I dunno if new ones still have the mechanical-style of choke.
Sometime this week I will do a cold start video with a new spark plug and post it here. I'm pretty sure the choke is acting correctly. I know the symptoms definitely lean towards a choke problem, and that's kinda where I started with the troubleshooting. I replaced the carb (I understand the choke is not controlled by the carb) and I'm getting the same issue as the last carb. It could be a mechanical input issue but I haven't been able to isolate it quite yet. I did pick up a fuel pressure tester, but haven't tested it yet due to an injury I'm recovering from.
 
The tubing I showed in message 45 is shown at the extreme right on message number 43 when the photo is opened up and much larger.

That tubing is VERY important to turn off the choke and fails often. Before you even start the genny next time, check that tube when the genny is COLD. Make sure it has no tears, holes and is in both slots. It is connected from the bottom of the choke box to the exhaust. Without that heat from the exhaust on the coke coil, the genny will run VERY rich when it warms up and then will die.

And it's such a common failure, buy a spare. You can get them on E-bay here.

-Don- Reno, NV
 
Understood, I will post a video showing the start up and failure. Prior to starting, I will definitely inspect the tube.
 
The choke does open right after starting. It is open before cranking, closes while cranking, and then opens after start up. This seems to be proper function to me. I will go over the parts for the choke assembly just to be sure there isn't any gremlins hiding there.

I too had a sticky choke. .When doing an oil change thy fixed it. I did not notice it myself. I should have but do not use the genny often enough t learn it's habbits.

I did find that if I added one step it worked better
Gasoline genny
press and hold stop till it lights.
Tap (not hold) start. Count a while (10-30) Press START and hold to VAROOM.
 
I too had a sticky choke. .When doing an oil change thy fixed it. I did not notice it myself. I should have but do not use the genny often enough t learn it's habbits.

I did find that if I added one step it worked better
Gasoline genny
press and hold stop till it lights.
Tap (not hold) start. Count a while (10-30) Press START and hold to VAROOM.
I will try this. I made the rookie mistake of setting up a video to show you guys the issue in action and didn't realize when I parked the rv a couple weeks ago, it was about 1/8 of a tank...lol. Genny will not run at that fuel level. This has not been the issue all along, just this last week. Need to disconnect and go fill the rv up, then make the video. The fuel level was one of the first things verified when the issue began, I just had a bonehead moment when relocating last time!
 

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