Cummins Onan 5500 question

JSS1439 wrote:
Thanks Chris, That's something else I was planning to do today. Run a couple gallons of fresh gas with Seafoam. I generally use Sta-Bil but seems people prefer Seafoam today.

Let us know how it goes. I've never had a lot of luck with either, but usually I'm dealing with a seriously clogged carb. I end up removing the carb and spraying a lot of carb/choke cleaner through the idle circuit openings and the main jets, etc. If that doesn't do it, I disassemble and spray, and if that doesn't work, it goes into the hot carb bath for 24 hours.

DryCamper11 wrote:

Chris Bryant wrote:
I also suspect a clogged idle jet- I would run some Seafoam through it. What happens is the throttle closes, but the idle jet doesn't provide enough fuel, so it opens up, but the main jet provides too much.....

Yes. IIRC, the idle jet is under a cap, so getting there is tricky. I drilled into my cap and put a screw into the hole to pull the cap off. I don't have experience with the carb in the HGJAB 5500, however.

Ok. Thanks for the edits. Got'em.

Chris Bryant wrote:
I also suspect a clogged idle jet- I would run some Seafoam through it. What happens is the throttle closes, but the idle jet doesn't provide enough fuel, so it opens up, but the main jet provides too much.....

Thanks Chris, That's something else I was planning to do today. Run a couple gallons of fresh gas with Seafoam. I generally use Sta-Bil but seems people prefer Seafoam today.

Chris Bryant wrote:
I also suspect a clogged idle jet- I would run some Seafoam through it. What happens is the throttle closes, but the idle jet doesn't provide enough fuel, so it opens up, but the main jet provides too much.....

Yes. IIRC, the idle jet is under a cap, so getting there is tricky. I drilled into my cap and put a screw into the hole to pull the cap off. I don't have experience with the carb in the HGJAB 5500, however.

Kpackpackkelley wrote:
There are different spec letters for the same gens. Look at your model number which starts with HGJAB so and so the spec letter is at the end of those letters and numbers on your data tag. It tells you which parts or manuals you need.

Ok thanks. That spec letter is E

JSS1439 wrote:
OK good info. Thanks again for your help, I'll play with the spring some more and see if it improves.

Read my edits for more info. :)

I also suspect a clogged idle jet- I would run some Seafoam through it. What happens is the throttle closes, but the idle jet doesn't provide enough fuel, so it opens up, but the main jet provides too much.....

DryCamper11 wrote:

JSS1439 wrote:
Hey DryCamper11, I adjusted that governor spring in both directions 3 notches and couldn't tell a difference. Any other suggestions that may help the "hunting" at low loads?

If it made no difference - set it back to where it was, then go through the troubleshooting section of the manual. I've got two Onans with the manual governor and one step in the setup is to adjust the position of that spring to increase sensitivity until it begins to hunt, then back it off until hunting stops. I find that hunting occurs most often at low power levels, and over the time, as the gen ages, I occasionally have to readjust it by moving it towards the end (away from the pivot shaft). That reduces sensitivity and decreases the tendency to hunt.

You can try moving the spring all the way to the far end to see if it stops hunting (just as a test), but that shouldn't be necessary in normal use.

If it's not a hunting problem, make sure you've disconnected all loads. I once saw a problem that looked like hunting, but it turned out to be a load that would start up, the gen would go full throttle trying to power that load, but before the gen could stabilize, the device would decide the voltage was too low and would shut off, so the gen would go back to idle. The cycle would repeat.

A microwave on partial power can make the gen do this, too, as the microwave cycles on/off to limit power.

OK good info. Thanks again for your help, I'll play with the spring some more and see if it improves.

JSS1439 wrote:
Hey DryCamper11, I adjusted that governor spring in both directions 3 notches and couldn't tell a difference. Any other suggestions that may help the "hunting" at low loads?

If it made no difference - set it back to where it was, then go through the troubleshooting section of the manual. I've got two Onans with the manual governor and one step in the setup is to adjust the position of that spring to increase sensitivity until it begins to hunt, then back it off until hunting stops. I find that hunting occurs most often at low power levels, and over the time, as the gen ages, I occasionally have to readjust it by moving it towards the end (away from the pivot shaft). That reduces sensitivity and decreases the tendency to hunt.

You can try moving the spring all the way to the far end to see if it stops hunting (just as a test), but that shouldn't be necessary in normal use.

If it's not a hunting problem, make sure you've disconnected all loads. I once saw a problem that looked like hunting, but it turned out to be a load that would start up, the gen would go full throttle trying to power that load, but before the gen could stabilize, the device would decide the voltage was too low and would shut off, so the gen would go back to idle. The cycle would repeat.

A microwave on partial power can make the gen do this, too, as the microwave cycles on/off to limit power.

Another possibility is that idle is too low, or the idle circuit in the carb is blocked. Either would cause the engine speed to drop too low and the engine might stumble. The governor would kick in with more gas, but if the settings are way off, or the carb is gummed up, you can see RPM oscillations similar to hunting.

I've opened and cleaned my carb on an old Onan I bought for $100, (Berrryman's soak for 24 hr in heated solution plus carb/choke cleaner) although the manual for most recent Onans no longer give the info on how to do this and just tell you to buy another carb. If you decide to open it up, let me know. There are some tricks to marking it during disassembly to get it back together correctly.

There are different spec letters for the same gens. Look at your model number which starts with HGJAB so and so the spec letter is at the end of those letters and numbers on your data tag. It tells you which parts or manuals you need.