Onan 5500 surging after warm

[dehaile]

Hello

I have a 2014 TH with an Onan 5500. After running perfect and warm, the unit starts to surge. If I hold the butterfly on the carb manually by hand just slightly closed,(it is wide open when it surges) the unit runs perfect. What would cause this? This unit has less than 50 hours on it.

Thanks for all the help.

[Sam_Spade]

ramgunner wrote:
A better bet is to use ethanol-free fuel with generators, etc. There are a number of sources for it in most areas.

That's rather hard to do when the gen sucks it's gas out of the main tank.

And ethanol is not the work of the devil. People got away with neglecting small engines a LOT with pure gas; not so much with ethanol blend. But.....it only takes a tiny bit of extra consideration and care for ethanol to work fine too.

[ramgunner]

A better bet is to use ethanol-free fuel with generators, etc. There are a number of sources for it in most areas.

[Sam_Spade]

Dirtclods wrote:
What octane are you running?

The recommended regular....for both the V10 and the Gen. (they share a tank).

There is absolutely, positively NO good reason to do anything else.

I give them a slug of Techron once a year right after the stabilized gas is mostly used up.

Well, maybe if the truck engine tends to ping under heavy load go up one step.

[Strabo]

Gotta use the gennys, let'm run!!!!

[Dirtclods]

What octane are you running?

[Sam_Spade]

dehaile wrote:
It surged after warm up in this configuration as well. I ran it two hours and it did not help.

Sometimes carb cleaner needs to sit in the carb overnight (at least) to really do it's job.

But on my Onan 4K, the carb had been cleaned professionally at least 3 times over it's recent life with only limited success short term. The Onan dealer said the offending passages are almost impossible to get cleared once they are really plugged badly.

A new carb has it running like new now for about 8 months. It had to go back once for a choke linkage adjustment.

[dehaile]

Thanks for the replys. I unhooked the gas line from the main tank and unhooked the fuel pump. I then connected a one gallon can of fresh gas mixed with b12 chem tool. It surged after warm up in this configuration as well. I ran it two hours and it did not help. I think I may need a new carb. I looked at the carb and it does not look like it comes apart to clean.

[Supereri73]

And I had a similar problem on my first toyhauler. The generator had 42 hours on it and was surging badly. I did 2 things and one of them fixed it

1) I plugged the trailer into itself. This trailer didn't have an autotransfer switch for the shore/generator power. I had to plug the shore power cable into the generator recepticle manually. This was unplugged when I first started working on the generator.

2) I replaced the gas with good gas.

One of those fixed it and I'm reasonable certain it was the gas.

If you don't know how old the gas is I would suggest getting it out of there and putting fresh gas in.

[Supereri73]

I know my Onan 4000 had an altitude adjustment, and based on a quick google search it looks like the 5500 does too. Have you looked at that?

Second, I've used carb cleaner to find vacuum leaks. You spray a small bit around the suspected areas and the idle raises. Could it be a air leak somewhere? Maybe some short bursts of carb cleaner around any vacuum lines or gasket connections?

[noteven]

Once in a blue moon patent medicines will clear a dissolvable bit of foreign material that is partially blocking a jet and starving the engine for fuel...

We clean up malfunctioning gasohol carbs by disassembling the carb, lightly blasting the metal parts with baking soda then boiling in hot water to clean up the soda residue. They look like new.

If you are doing a camp spot overhaul where air compressors and soda blasting guns are frowned on, sometimes a good boiling will remove the gasohol induced crud.

Avoid the urge to poke sharp metal objects through the jets and passages and get rough with stuff... fine copper wire...

High possibility this will not work on rv.net carburetors of course.

[Snowman9000]

Sam, all I can say is that my experiences are as reported. They are not marketing claims. And I was skeptical going in. All this stuff screams snake oil to me.

[Sam_Spade]

Snowman9000 wrote:

Are you a chemist?
Have you tried it?

And the kind of buildup that could be on injectors in the combustion chamber is quite a bit different than what's in a dirty carb.

Yes sort of. I studied Chemical Engineering but never finished.

Yes I've tried a LOT of stuff over the years and have figured out which "information" to trust and which not. Marketing claims fall into the NOT category.

There aren't many GAS engines that have direct injection yet; maybe none ??

[Mnflyboy]

It runs good until the auto choke opens....that's what mine did when I bought it. The person I bought it from knew it and only demo'd it for a couple of minutes cause he knew what would happen when it warmed up. I took the carb apart 3 times to get it clean enough and now it runs great. They say it is non-serviceable...but it does come apart if need be. Try the portable tank/cleaner trick first...then get the wrenches out...new is $250ish....I will clean that bugger quite a few times for that much money.

Jaye(Mn)

[Snowman9000]

Sam Spade wrote:

Snowman9000 wrote:
Actually I have had even better results with Sta-Bil Marine additive than Sea Foam.

And you should have even better results if you use a product that is designed to be a cleaner.

Both those were intended to be a fuel stabilizer and whatever cleaning action they have is just a coincidence. Gumout and Berrymans B12 are better cleaners. Techron for engines with injectors.

Are you a chemist? Sea Foam is marketed to clean out carbs. The Sta-Bil Marine formula I have also has directions for using it double strength to clean out carbs. I've used Sta-Bil Marine for this exact purpose, several times, and it worked great. That is my only qualification to be able to comment here. Have you tried it?

And the kind of buildup that could be on injectors in the combustion chamber is quite a bit different than what's in a dirty carb.