Generator Carb Problems

[garageman402]

We have a Cummins Onan QC 4000 generator on our RV that doesn't get a lot of use. It was last run in August, & has been inactive ever since (about 7 months). Now it won't start. Our RV dealer doesn't work on generators, they sub it out, & there's warranty questions, so the shop foreman tried to get it going. He said when they sit like that, the carb gets gummed up from old fuel. He got it to run on carburetor cleaner, but that's all. He advised taking the fuel hose off & running Sea Foam through it. The hose is attached with a crimp clamp which I don't want to tamper with if it will void the warranty. The carb bowl has a drain valve which I have opened, & primed, fuel comes out when the pump is running. So we know it's getting fuel, we know it's getting spark, because it runs on carb cleaner. I attempted to spray Sea Foam & Gumout carb cleaner in through the drain plug.

The generator feeds off the main fuel (gas) tank, but only down to 1/4 tank so you don't get stranded. This is a 60 gallon tank, so I need to treat the whole 60 gallons to get it to the generator.

My question is what kind of fuel treatment would I use? Sea Foam is oil based, not sure if it would be effective. I'm assuming a PEA additive would be ideal? Would (3) 20oz bottles of Techron be a good start? I can get it to fire by holding the choke closed after priming, but it only lasts a few revs with choke closed or open.

 

[Jdeere562]

#1, don't use gasoline with alcohol, Top Tier. Then add a fuel stabilizer on top to prevent that in the future.

 

[ripcord]

Sounds like the carb needs to come off for tear down and cleaning.

 

[chemman]

If you desire a gasoline additive that will clean a carburetor while the engine is running, use Berryman B-12 Chemtool. It is orders of magnitude more powerful than Seafoam.

I had a problem with the carburetor on my gasoline powered 5 KW generator related to varnish from fuel, and by using Berryman B-12 Chemtool in an aerosol can, I was able to clean the varnish and other crud out of the carburetor and avoid having to pull the carburetor and rebuild it a handful of hours before Hurricane Sandy approached Maryland and knocked out our power. I also added about 8 ounces of Berryman B-12 to every 5 gallons of gas, and the generator ran flawlessly for 60 hours straight after we lost power.

Good Luck!

 

[UncleDave]

This gen is famous for this, the micro quiet 4K. Every gen set shop has a garbage can full of these carbs.

At this stage with this genset id replace the carb and religiously drain it going forward.

I wouldn't worry so much about the treatment of the fuel if you drain the carb religiously.

 

[mk378]

If you have access, remove the carb bowl then spray cleaner directly through the main jet using the tube on the can. If it's a typical Honda clone, the jet will be inside the center part that receives the bolt that holds the bowl on. If it's severely gummed you may need to poke through the hole in the jet with a wire. Obviously having a carb that is detached from the engine will help to see what needs to be done.

Cleaner in the tank really can't do much unless there is some flow to begin with.

 

[UncleDave]

If you have access, remove the carb bowl then spray cleaner directly through the main jet using the tube on the can. If it's a typical Honda clone, the jet will be inside the center part that receives the bolt that holds the bowl on.

It's not a Honda clone.

The carb is really unique and cool in that it has an elevation knob on it, but there is no rebuild kit available and it's famous for gumming if you arent religious about draining.

 

[oldcodger]

Probably save your self a lot of time if you just replace the carb.

 

[UncleDave]

Sounds like the carb needs to come off for tear down and cleaning.

Thats what I thought when I had this problem with this same unit, and although I got it started I couldn't keep it from surging.

 

[JohnnyG]

Why replace the entire carb? I have fixed MANY carbs over the years by just taking off the fuel bowl, removing the main jet and cleaning it out. In this case especially, I don't think this generator has that many hours on it, so I doubt that anything will be worn out.

I cleaning the jet doesn't work, THEN think about getting a new carb. Oh. and the "quick and dirty" just add some cleaner, has never worked for me.

 

[UncleDave]

Why replace the entire carb? I have fixed MANY carbs over the years by just taking off the fuel bowl, removing the main jet and cleaning it out. In this case especially, I don't think this generator has that many hours on it, so I doubt that anything will be worn out.

I cleaning the jet doesn't work, THEN think about getting a new carb. Oh. and the "quick and dirty" just add some cleaner, has never worked for me.

Why replace vs clean - I've already addressed "why" as this particular carb is a noted pain and the best experience is firsthand experience which I've proffered.

OP is free to do as he sees fit however.

As my track record of cleaning was similar to yours I tried it myself asked the same question to other guys that tried it, and one of the best gen set shops I could find and used laughed at me and showed me a bin full of these exact carbs.

 

[chainblu]

Looking to the future, is there a fuel shut-off valve going to the generator? If so, running it out of gas when you're done with it might help with this problem going forward.

 

[garageman402]

Why replace vs clean - I've already addressed "why" as this particular carb is a noted pain and the best experience is firsthand experience which I've proffered.

OP is free to do as he sees fit however.

As my track record of cleaning was similar to yours I tried it myself asked the same question to other guys that tried it, and one of the best gen set shops I could find and used laughed at me and showed me a bin full of these exact carbs.

Thanks for the advice, I see you're in CA, which gen shop would you consider the best? I'm in the Modesto area now, my RV dealer recommended Industrial Electric, but they never answer their phone or return calls. "Red Barn" in Salida was recommended by another rv dealer, the foreman there very friendly & knowledgeable but won't do warranty. He said it's expensive to get Cummins certified & he doesn't do enough of that type of business to justify it. He mostly does sprayers & ag equipment.

 

[garageman402]

Looking to the future, is there a fuel shut-off valve going to the generator? If so, running it out of gas when you're done with it might help with this problem going forward.

Thanks, no shut off that I have found (yet) but it will run out if main gas tank is below 1/4, so I could do that or just drain it. Good advice, I wish the RV dealer mentioned that on the walk-through, instead of recommending putting peppermint oil around the fridge vent....

 

[SC Maintenance]

Looking to the future, is there a fuel shut-off valve going to the generator? If so, running it out of gas when you're done with it might help with this problem going forward.

^^^ This is what I was going to recommend. What kind of fuel line is it? If its just a rubber hose -you could add one right near the carb.

 

[garageman402]

Why replace the entire carb? I have fixed MANY carbs over the years by just taking off the fuel bowl, removing the main jet and cleaning it out. In this case especially, I don't think this generator has that many hours on it, so I doubt that anything will be worn out.

I cleaning the jet doesn't work, THEN think about getting a new carb. Oh. and the "quick and dirty" just add some cleaner, has never worked for me.

^^^ This is what I was going to recommend. What kind of fuel line is it? If its just a rubber hose -you could add one right near the carb.

Yes, rubber hose, I could put an inline valve there, but I'm thinking closer to the filter would be better. I haven't looked myself, but I've seen YouTube videos showing how to access it.

 

[garageman402]

#1, don't use gasoline with alcohol, Top Tier. Then add a fuel stabilizer on top to prevent that in the future.

The only place I have found ethanol free gas is in Texas at Buc-ee's & I think QT, but it's $1 more than regular 87 per gallon. It is 90 octane, tho. In a 60 gallon fuel tank that's +$60! Some of the stations in the hill country (in fact all of them) have 86 octane, which I have used at higher elevations. Fuel stabilizer is a good idea, though. I admit, I haven't been diligent about getting TopTier gas, it burns so much I get what I can as cheap as I can. At home I will fill up with Costco 87 TopTier.

 

[garageman402]

I don't think this generator has that many hours on it, so I doubt that anything will be worn out.

Yes, you are correct. I forgot to mention we bought it in Dec 2020, the house is a 2021 model, the cab & chassis is 2020. I can't recall how many hours are on it, but I think around 100.

 

[UncleDave]

Thanks for the advice, I see you're in CA, which gen shop would you consider the best? I'm in the Modesto area now, my RV dealer recommended Industrial Electric, but they never answer their phone or return calls. "Red Barn" in Salida was recommended by another rv dealer, the foreman there very friendly & knowledgeable but won't do warranty. He said it's expensive to get Cummins certified & he doesn't do enough of that type of business to justify it. He mostly does sprayers & ag equipment.

I was in So cal, and it was called Oliphant - a light year away from Modesto.
I'll make some calls when I get back into town next week.

 

[Sequoiasoon]

Why replace vs clean - I've already addressed "why" as this particular carb is a noted pain and the best experience is firsthand experience which I've proffered.

OP is free to do as he sees fit however.

As my track record of cleaning was similar to yours I tried it myself asked the same question to other guys that tried it, and one of the best gen set shops I could find and used laughed at me and showed me a bin full of these exact carbs.

How much is one of the carbs? How hard to replace? Are they available?

Not the same probably as the RV mounted ones.

The carb on my snowblower was leaking and engine surging. Rebuild kit was $12. The whole new carb with primer, hoses, gaskets, throttle handle, choke knob was $18. Yup replaced it.

My old hand me down generator with Briggs motor I couldn't get a carb for under $150 and even they were limited. I took it apart and fortunately was able to clean it up. Learned from those like Uncle Dave. They all have fuel shutoffs now. I also run some TruFuel or VP Racing through them first, then shut fuel let it run out. Restart 2-3 times as it sits, then drain the bowl. No matter what fuel it will evaporate out of bowl sitting and leave all the junk. Old snowblower had issue every year (sat in shed in sun). Shop finally said We love helping you but all we do is clean out your red Stabil every time". Told me to do as above and no issues since. I still go there for other services, parts, 2 stroke and VP ethanol free. Hard to find an honest place, I try to support those that I do.