Calling all GX390 experts


It could be. Do you have it bypassing to a buffer or anything? I’m 99% sure mine was carb (fuel) related. I have a handful of jobs to do when I get back in town so hopefully I resolved my issues. How does your engine sound under load? Is it spitting, sputtering, or backfiring when you try to use high pressure?


I was honestly skeptical of the high-octane suggestion, myself. And I’m still not 100% sold on the logic of the idea. But I’ve now heard it from enough different mechanics (some of whom claimed to receive the info from Honda sources), that I’ve gone out on a limb and started using the premium.

I can understand that you’re running a large operation, and making a switch to a more expensive gas would need to be based on solid evidence. But thankfully, the switch for me will amount in only a few bucks a week more for fuel. I can take that kind of gamble, lol.


I don’t have it bypassing to the buffer. I want to just haven’t yet. I haven’t noticed any of that happening. Just not a lot of pressure


Here is a link that you can use to find non-ethanol gas in your area.


Reason i ask about bypassing to a tank is then you could see what the unloader is doing on and off trigger. When you’re on trigger you only want a small amount of water (I think) being bypassed into the tank. At least then you would be able to see what your unloader is actually doing. A gx390 tune up kit is less than $30 on amazon/eBay. I would recommend getting one of those first. (Carb, air filter, fuel filter, and spark plug). Fingers crossed that’ll be your fix. Someone else will have to help on how to evaluate your unloader.


Low water supply


Hi Alabama,

I run a pair of GX390’s, mine use General 4040G pumps. One machine is 5 seasons old, the other is 4. Each machine has several thousand hours of run time. I’ve experienced the same problem as you. I see from your recent update that your machine is running good again after another new carb. I’m concerned that a can of bad gas might be causing your trouble over and over, and it might happen again.

An excellent local mechanic gave me this tip years ago, and it has worked like a charm for my machines:

Once every month, or any time the machines will sit unused for a while, fill your empty tank with “Av Gas” and run it like normal. Aviation gas is available from the field pump at tiny airports or even hotrod shops… the type many small towns or rural counties have. I thought it was odd but I walked right up to the little terminal with my gas can and the kid on duty told me that all the local landscape companies often get gas there, too, because it cleans out the fuel system.

Seems that the Aviation fuel has no ethanol, is leaded, and has stabilizing additives. In my experience it can sit for ages and not go bad. No, the higher octane won’t hurt anything in your GX (but don’t put it in your car!). On the rare instance that I’ve had to replace a carb, I’ve realized in hindsight it was when I also hadn’t run the AvGas through the machine in a long time.

Give it a shot. It sure has helped me keep mine machines running like they should.


Replied to an old post…


Great info there, thanks.

Also, you have a great website. Do you mind saying about how much it was? If you would rather not, or would rather PM it, no problem. Kudos to whoever did it.


Dude that is awesome and thank you for the tip!! I’ll definitely start doing that. We have an airstrip 15 mins from my house.

Thank you!

Nick Wheeles
Wheeles Washing Services
~Home of Sir Wash-a-lot~


Good tip there