Generac running rough.

[WHGuy413 2,690]

Hey everyone I’m stumped and in need of some input. Usually I can figure these things out and thought I had this one fixed. I have a Generac GP7500E that is a friends of mine. He dropped it off for me to fix after sitting for 5 years with a full tank of gas. He recently used it for 20 minutes when he lost power and it died after that. The carb was gummed up so I cleaned it top to bottom and inspected all the gaskets and reinstalled. It started on the first pull and was running excellent for about 10 minutes when it started “hunting” for rpm’s. If you had a little tiny bit of choke it smooths out. So I took it all apart and cleaned it again this time finding absolutely nothing in the carb. Every passage, the bowl and the inside of the carb are clean with no sign of loose debris. Reinstalled and it started on the first pull again. Ran excellent for about 5 minutes again then started hunting again. What am I missing? Carb is clean in every passage, gaskets are all good, air filter is clean. 

[OutdoorEnvy 1,522]

Could be a gasket leak and is getting too much air after it warms up.  Also the coil might be going bad and but that seems less likely since it smooths out with the choke adjustment.  You could also check for a muffler blockage.  Especially if it has a spark arrestor screen or something on it.  Also something else that I've had pop up from time to time with after market air filters is sometimes one breaths too much or not enough and run into issues like this.  Maybe check if it's the actual OEM brand on it and try that first before doing the other stuff.  That's all I got offhand on it.  Best luck with it!   

[Achto 27,597]

18 minutes ago, WHGuy413 said:

Generac GP7500E

 

And in comes a Generac employee.  Truthfully I don't have much experience with the portables, I trouble shoot & test 100kw - 2000kw at the plant that I work at. Couple questions though.

 

1 - is the fuel tank clean

2 - is the screen on the petcock clean

3 - is the filter and lines clean

Could be picking up some small debris from the tank or lines. If everything is clean and good maybe try running some Sea Foam in the gas to help clean things out.

4 - is the output voltage good when it's running correctly

Bad AC voltage can cause hunting on some models. On the other hand engine hunting will definitely cause erratic voltage. Can be hard to pin point this issue if you have a electronic controller which I don't believe that you have. 

Edited January 5, 2023 by Achto

[WHGuy413 2,690]

12 minutes ago, Achto said:

 

And in comes a Generac employee.  Truthfully I don't have much experience with the portables, I trouble shoot & test 100kw - 2000kw at the plant that I work at. Couple questions though.

 

1 - is the fuel tank clean

2 - is the screen on the petcock clean

3 - is the filter and lines clean

Could be picking up some small debris from the tank or lines. If everything is clean and good maybe try running some Sea Foam in the gas to help clean things out.

4 - is the output voltage good when it's running correctly

Bad AC voltage can cause hunting on some models. On the other hand engine hunting will definitely cause erratic voltage. Can be hard to pin point this issue if you have an electronic controller which I don't believe that you have. 

Fuel tank is spotless. I’m going to try replacing the fuel lines but they seem to be working just fine. Filter is clean. I will pick up some seafoam tomorrow. 

[WHGuy413 2,690]

17 minutes ago, OutdoorEnvy said:

Could be a gasket leak and is getting too much air after it warms up.  Also the coil might be going bad and but that seems less likely since it smooths out with the choke adjustment.  You could also check for a muffler blockage.  Especially if it has a spark arrestor screen or something on it.  Also something else that I've had pop up from time to time with after market air filters is sometimes one breaths too much or not enough and run into issues like this.  Maybe check if it's the actual OEM brand on it and try that first before doing the other stuff.  That's all I got offhand on it.  Best luck with it!   

Thanks for your reply. The generator has less than 20 hours on it so I’m assuming it’s still the original parts on it. I’m assuming it’s a fuel delivery issue but can’t seem to figure out where. The gaskets all look great with no tears. I know personally I have put some pretty questionable gaskets on personal stuff and had them run much better than this but you never know.

[Achto 27,597]

6 minutes ago, WHGuy413 said:

I will pick up some seafoam tomorrow. 

 

The engine is basically a Honda clone. I've had issues with the fixed jets on this style of carb. Fought with a Harbor Freight engine (another Honda clone) on a log splitter for one season having to run at 1/2 choke to get it to smooth out. Final resolution was to drill the main jet out one size bigger. This was the cure for that engine not saying that it is the cure for your engine.

[lynnmor 7,307]

Maybe there are passages in the carburetor that are hard to see or hidden behind a welsh plug, look at a diagram of the carburetor.  Are you using fresh regular grade gasoline with no more than 10% ethanol?  Is the fuel tank vented properly? 

[953 nut 55,283]

1 hour ago, WHGuy413 said:

I will pick up some seafoam tomorrow.

            Also try spraying some carburetor cleaner in the air intake while it is running. This has done the trick on a couple undependable engines I've had.

[Blasterdad 2,692]

Usually when a small engine starts "hunting" its a clogged jet.

 

[Jeff-C175 7,202]

I've got B&S on a snow thrower that does that, I gave up and just run it with partial choke.

 

Fixed a Duromax genny for neighbor, had to drill out the jet.

 

It's the epa's fault for demanding low emmissions and the fixed jets.  Just too damn lean.

 

 

 

.

 

Edited January 6, 2023 by Jeff-C175

[8ntruck 7,014]

I have a B&S on my tiller that hunts unless I put one notch of choke on.  I have not gotten back to it yet.  When I do, I am planning on running torch tip cleaners through the jet. 

 

@ebinmaine had  B&S that hunted a while back. He inspectedcted the carb on his second cleaning under better light and magnification and found some crud still in the main jet.

[WHGuy413 2,690]

1 hour ago, Blasterdad said:

Usually when a small engine starts "hunting" its a clogged jet.

 

I thought the same thing. I’ve been into the carb a couple times and every passage and hole is open. It’s odd to me that it runs great for 5 minutes then starts hunting.

[WHGuy413 2,690]

1 hour ago, Jeff-C175 said:

I've got B&S on a snow thrower that does that, I gave up and just run it with partial choke.

 

Fixed a Duromax genny for neighbor, had to drill out the jet.

 

It's the epa's fault for demanding low emmissions and the fixed jets.  Just too damn lean.

 

 

 

.

 

Couldn’t agree more. The old style adjustable carbs are much better. 

[WHGuy413 2,690]

26 minutes ago, 8ntruck said:

I have a B&S on my tiller that hunts unless I put one notch of choke on.  I have not gotten back to it yet.  When I do, I am planning on running torch tip cleaners through the jet. 

 

@ebinmaine had  B&S that hunted a while back. He inspectedcted the carb on his second cleaning under better light and magnification and found some crud still in the main jet.

If this was for me I would be ok with it running on one click choke for a little while. But being for a friend who is willing to pay I want it leaving running right. I’ve run torch tip cleaners in every hole, and brake clean in every hole. I’ve never had issues before like this. I’ve been into hundreds of carbs over the years and a good slow careful cleaning usually does the trick on the first attempt. I’ve had to take a few apart a second time but it’s not often. This one is just being difficult. 

[Blasterdad 2,692]

8 minutes ago, WHGuy413 said:

I thought the same thing. I’ve been into the carb a couple times and every passage and hole is open. It’s odd to me that it runs great for 5 minutes then starts hunting.

Try a new fuel filter too, sounds like crap may be getting back in there or it is restricting the flow... 

[Jeff-C175 7,202]

14 hours ago, Blasterdad said:

 restricting the flow... 

 

Like pulling a vacuum on the fuel tank...

 

 

Edited January 6, 2023 by Jeff-C175

[Blasterdad 2,692]

5 hours ago, Jeff-C175 said:

 

Like pulling a vacuum on the fuel tank...

 

 

@Jeff-C175 brings up a good point, check the vent in the gas cap, or CARB compliant system if so equipped...

[rmaynard 15,502]

13 hours ago, WHGuy413 said:

I will pick up some seafoam tomorrow. 

 

Considering that I don't believe in snake oil remedies, I will be following this. 

[squonk 41,137]

My neighbor had a C-160 that couldn't get out of it's own way. It had a junk Walbro carb on it that I had no parts in stock for and he didn't want to invest in a kit or replacement. A heavy dose of Seafoam got it running.

15 hours ago, Jeff-C175 said:

I've got B&S on a snow thrower that does that, I gave up and just run it with partial choke.

 

Fixed a Duromax genny for neighbor, had to drill out the jet.

 

It's the epa's fault for demanding low emmissions and the fixed jets.  Just too damn lean.

 

 

 

.

 

Reminds me of Chrysler's "Lean Burn" system that all of us in the shop relabeled as "Never Burn" 

[Jeff-C175 7,202]

5 hours ago, Blasterdad said:

CARB compliant system if so equipped

 

Probably is.  Should be a tube coming up to the top of the tank to a fitting on top if it is.

Mine got messed up at one point after a period of no use and actually somehow was pressurizing the tank!  There was raw gasoline weeping out from around that fitting.  Then it just stopped doing that, and it's been fine ever since.  Must be some sort of check valve, like a PCV valve and it got 'stuck'.  I'm guessing!

 

Edited January 6, 2023 by Jeff-C175