Honda GX 160 Engine -- erratic running

[SouthWestern]

Still struggling with this one; after carb clean and new pilot jet, fresh fuel, just to recap:
The engine starts smoothly and easily, and seems to run great at low revs.
After a minute or so at high revs, it starts to cough, splutter and backfire.
Then it may burst back into life and seems to run fine for a short while before repeating the process.
Can anyone think of anything specific that might cause this behaviour?

 

[Auto Doc's]

Possibly a wrong spark plug. Verify you have the correct plug it calls for. If it has an Amazon plug, those are almost guaranteed to be bad.

The next suggestion is to pull the fuel tank and remove the tank fuel nipple to clean it.

 

[Forest#2]

Most generally about the only thing that is reasonably priced about Honda engines is a replacement carb. (and I've had good luck with the Honda carb replacements)

This is just one of the examples of where a Ultra sonic cleaner really shines.
I've tried just a general cleaning of (especially) the Honda carbs and if they still surge I send them to the USonic and usually get a good run and not even have to install a kit. If they still surge and hunt I try a cheap replacement. If the bowl is rusty it's a hint you need to replace, it's probably had ethanol fuel inside and the fuel lines are also going bad internally.

One some of the Honda powdered equipment they hide a fuel filter on the end of the fuel line poked into the plastic fuel tank. If it's restricted it can cause erratic surging and hunting.
Lots of info on-line about this in tank filter that is on the end of the fuel line on some Honda powdered Equipment.

 

[SouthWestern]

I am going to take the tank off and clean it (again) but I am a bit uncertain this is going to help: if I take the fuel line off the carb then fuel literally jets out.
The engine is not really hunting and surging: it virtually dies with just a few pops and coughs... then usually recovers. If I turn the fuel off at this point, (to test if the carb is now empty) it may still recover and run or run/cough/run for a while before finally stopping for lack of fuel - as you would expect with the tap off. A puzzle.

The engine would not run at all when I started - I just emptied the bowl, cleaned the bowl and main jet and it the started fine with fresh fuel - but with the erratic problem. Part of my second carb clean was an ultrasonic clean of the whole thing (as well as detailed cleaning/replacement of jets) there was no discernable difference after all that! So that maybe points away from the carb... let's hope the answer lies in the tank.

 

[Auto Doc's]

This is starting to sound like you have some bad fuel in your gas can from a station recently.

I consider any fuel without a stabilizer "bad fuel" after 15 days here in South Texas, due to the heat and humidity.

I have also had these "self-inflicted" episodes just from leaving a fuel can sit open in a shed when there is high humidity.

Ethanol fuel is "hygroscopic". That is a fancy word which means it absorbs moisture from the surrounding air.

Most people never check their fuel cans/jugs and just keep putting new fuel in when they get at or near empty.

To verify: Empty most of your fuel can into one of your vehicles then remove the nozzle from the can and look at what is left behind in the fuel container bottom. Usually trash from dust and cut grass along with a little water stays behind.

Flush out your fuel can really well with water, then let it sit to dry out upside down (without the nozzle installed) for a couple of days. After that refill the can with new mid-grade fuel from a reputable station. Don't use the low budget Ethanol fuel. If you have a none-Ethanol fuel available, that would be even better.

A product called Ethanol Shield works really well and lots of professionals use it. Sta-bil has lost popularity in recent years because it is not living up to its claims (from my own personal experience).

Teryl Fixes All (You Tube) has conducted several tests on fuel stabilizers, so check out his videos. Chickanic is another great small engine repair tech who has also verified Ethanol Shield is some great stuff.

 

[Forest#2]

Install a new spark plug, but it has symptoms of bad water contaminated fuel.
After you clean the tank use fresh fuel from a different container. The symptoms you describe indicates bad/water contaminated fuel, but
If it's a push mower with the presence switch lever make sure the brake, kill is not at the critical point of interrupting the engine kill. Sometimes it gets at the vib critical point of ignition run, kill on the brake cable.

Also monitor the spark with a Briggs or Oregon 19051, 19368 spark tester. $15
Connect it in-line and watch the spark through the view window while the engine is running.

Do not rely on a light bulb type ignition tester.

 

[SouthWestern]

I'm in UK, so standard grade petrol/gasoline has 10% and "super" 5% Ethanol. So we have to live with that... having said that it normally works fine, I think as long as the engine is in regular use. I use an alkylate like Aspen or an additive over winter on anything which is not in regular use.
But bottom line, I need to look at both tank/fuel and thge spark plug next.
PS: Chickanic has a great channel and helped me with a few chainsaw problkems!