Onan Gen--hard starting and surging

[RustyMacIntosh]

I was gifted a 95 Bounder 34ft with the big block Ford engine. 30kish miles. Sat a lot.

I've resurrected it back to 90% operational. I've made several statewide trips.

The generator. At first, it would not start. Now it starts after cranking maybe 30 seconds from the dash. It will start up, run for maybe 5 minutes then you can feel it begin to surge.

Opening up the side panel, it's running, smoother now that at first. But then it surges. It gets worse and worse surging, then quits. It might attempt to start again but dies like it is out of fuel.

Let it sit for several hours, it does the same routine, cranks (longer than I like), then fires up, smooth then begins to surge ultimately dies.

OK--the coach has gone thru maybe 10 tanks of gas. Including filters and treatment. The 460 runs nicely.

I was once told that this unit has a fuel pump. So far, I have not located it.

I can see the filter which is connected to the carb. I tried yesterday to remove the filter but was unable to get the brass connector to free up from the bottom of the filter. I'm going to try it again today with heavier tools.

I think it is running a bit rich. Or at least that is what the exhaust pipe looks like. I do not see any blue or black smoke from the exhaust.

I'm thinking that maybe its time to just swap in a new carb, a new filter and all. Fuel pump? I guess if I can find it.

Its the Onan 5000 model btw.

[RustyMacIntosh]

The genset appears to have all the whistles and bells with a choke pulloff, heater on the choke itself, but no enrichment adjustment that I can find. It does have that black carb bowl that allows the owner to adjust from 0 to 10,000ft.

I got it to run for a while yesterday, which is more than it ever has run. It was idliing for quite a while when I turned on the back AC to give it something to work at.

The gen seem to run OK but once I turned off the AC within a minute it started to surge again, then shut down. I've got an idea to plumb in a line with BG carb cleaner while it runs before I spring for a carb replacement.

It is 90% running smoothly, just that nasty surge keeps springing its head back up. I am sure it just needs to run some more. I hope it will self clean whatever garbage is still in the bowl with clean high quality detergent gas.

[77rollalong]

If it has sat for quit a while, best bet is to pull the carb off and get a container of the really good carb cleaner from napa or auto zone.. the one I got was marked professional use only, as it will dissolve plastic and rubber parts and wear rubber gloves, hard on skin.. like paint stripper.. there should be and adjustment for the idle mix on the carb you could try tweeking that a bit as well. Not sure if yours has an auto choke pull off from vacuum or not, mine is a heater type pull of so it takes a bit of messing about to get it right as well as it takes about 2 min to completely pull off when first started and runs a bit lumpy. ours is the original gen set in out 1977 motorhome ..

[RustyMacIntosh]

it's a 5000
I have douched the carb several times with Seafoam, letting it sit overnight. I would block off the inlet fuel line, let the genset run a few seconds, then pump Seafoam in that tiny plastic spray tube they supply, into the fuel line that runs to the carb.

Also, I took the air cleaner off the carb, spraying Seafoam all over the choke butterfly. Also let it sit overnight.

I think I fouled one plug. So I changed both spark plugs this morning, including dropping the extension and spark plug socket down the back of the generator.

This AM it fired up, smoked a bit then settled down to a nice idle. After it warmed up I turned one AC unit on. Everything was fine until I shut the AC off after letting the gen run for 30 minutes,

Then the surging began again. I am thinking for the time being to just fire it up several times a day letting it run as long as it can using clean fresh fuel from the main tank that has Techroline additive.

Sooner or later I am sure I am in for a carb replacement. Fuel filter is clear, the pump is pumping...it just does this surging thing then ultimately shuts down.

https://ibb.co/gJqgFjr

The gen has 501 hours on it btw.

[RLS7201]

Rusty if you have a 5K Onan in your 95 Bounder, it has been changed. In fact, I don't believe Onan made a 5K 120 volt gas generator for RV service. I sure would like to see a picture of the data tag on that generator.
95 Bounders came with an 4K BGE Onan with one Air Conditioner and a 7K NHM Onan with two Air Conditioners.

Richard

[RustyMacIntosh]

Going to give it a try today, I bought several cans of a brand name carb cleaner at Wallyworld once the sun is up, the dogs are satisfied, I will get my stool out then work on the carb.

[olfarmer]

I would use some spray on carburetor cleaner rather than seafoam.

[ksg5000]

For what it's worth - soaking the carb with a bit of Seafoam for an hour isn't sufficient. You need to soak 8+ hours and then repeat as necessary. Your trying to remove 20 years of crud. If it were me I would load the carb with Seafoam and let it set at least a day.

[10forty2]

RustyMacIntosh wrote:
This morning it is spilling fuel from the air cleaner which mounts to the opening of the carb. I gotta get this carb torn down to check the needle and seat...

I'd bet the float valve is stuck open, allowing fuel to continuously flow into the bowl.

[RustyMacIntosh]

This morning it is spilling fuel from the air cleaner which mounts to the opening of the carb. I gotta get this carb torn down to check the needle and seat...

[rrupert]

Check out the YouTube videos for Onan RV Generators:Onan

[10forty2]

When we first got our coach, the genset would not run. It would turn over, but would not run. After a little studying, I figured out that it was getting plenty of fuel from the fuel pump, the fuel line was in good shape, and it had plenty of spark.....only thing left was the carb. I figured out how to disassemble the carb..removed the bowl...removed the needle valve and found the float to be slightly stuck in the closed position. Seafoam to the rescue! I put all the removed components in a bowl of Seafoam and let them soak for an hour or so, and then used a wire brush to remove all the varnish that had accumulated from the crappy gasoline. Put it all back together, and WAL-Ahh! She fired right up, ran like a sewing machine, and has been running great for the past 5 years. I put Seafoam in every tank of gasoline in the RV mixed at 1 oz per gallon of fuel. Primary engine runs great, and so does the genset!

[RustyMacIntosh]

My unit is a 5000, not a 5500. The carb faces the rear of the coach.

I never could get the brass connection to the bottom of the filter. So I cut the line leading to the filter, from there I removed the filter, blew out any fuel and gunk that might have been there.

After removing the filter from the carb, I pumped some SeaFoam spray down into the carb. Cranking the motor just briefly I could then determine the fuel pump is working...so the line was plugged with a bolt so I could crank the motor without getting a face full of gas.

I got it to start with the inlet fuel line loaded with Seafoam sorta kinda. I opened up the connection to the carb from the air filter, where I sprayed the innards also with Seafoam.

It ran better----smooth, after connecting back the inlet fuel line. UNTIL I put some load on it. Then the surge came back slightly, then got worse and worse until it quit.

I fired it back up, this time playing with the throttle, I am guessing that there must be a FAILSAFE that if the RPM's get too high the unit shuts off. I tried to get the RPM's up higher to see if it would self-clean with some fresh gas from the main tank, but nope...nada.

Opening the fuel line back up I poured more Seafoam into the line leading to the carb, where I let it sit for an hour. Again, it surged and finally quit.

SO.....I guess I will try one of those carbs off Ebay. I see I can get one for about $50-60 bucks. The swap looks easy enough. I am sure if I take it to the Cummins shop they will sell me a new carb at $400 plus labor.

One thing I did do is blocking the inlet gas line with a bolt, I checked after cranking to see if any of the leading gas lines from the main tank were wet indicating a crack. None.

**Footnote** The adjustment at the bottom of the carb for altitude, I have it set at Sea Level. If I turn it to 5000 or upwards the unit really does run rich.

I guess I could try some more carb cleaner, like BG or another product, but it appears whatever is going on with this Genset, the years of sitting in that storage yard has destroyed the carb just enough that it does not want to operate anymore.

[RLS7201]

Your Onan NHM 7K generator has an adjustment on the bottom of the carb for different altitudes. Try turning the screw counterclockwise for a slightly richer mixture, and see what happens.
The ethanol in the fuel is actually a solvent that helps keep the carb clean. Remember when we used to add ethanol to our gas to help pass any water that was in our fuel tanks. Now we don't need to do that.

Richard

[gbopp]

I had a surging problem on the Onan 5000 in our 96 Southwind.

I used a can of Spray Seafoam. I removed the air filter. With the generator running I sprayed the Seafoam into the intake until it almost stalled.
I did that several times, then sprayed until it stalled and left it sit overnight. The next day it ran smooth.

Try that a few times, it's cheap and easy. Leave it sit several hours after stalling the generator with Seafoam.
I left it sit overnight because I was busy with another project.