Gx390 engine issues

Hi all,

I have a gx390 2500 psi 5.5 gpm, sat all winter with antifreeze in pump, ran machine till it died out and used siphon pump to remove gas, did not get all off it out. Now as I’m getting ready to start up again I changed oil, pump oil, new spark plug, new filter. Machine would not crank over. Cleaned out carb, and she ran but really rough. Replaced with new oem carb, she sounds better and runs smoother but not like it use too run, but once I close ball valve to create pressure it dies out, and also get some back firing. I’m stump any suggestions please, I have video I’m trying to up load, I have been searching day and night for answers to this problem.

After I cleaned carb out

New carb, sounds better but not there yet,
If I close ball valve for pressure dies out, I did get high pressure for a good minute she back fired, and wanted to die out, open ball valve and it stayed on.

Honda carb or something off of Amazon?

Oem carb, not from amazon

Make sure you put linkages back correctly, and check that you didn’t over torque the spark plug. Lastly, make sure the rubber tube from valve head to carb is good and also tight.


Oh yeah, also, is your water source open, as in is the engine sucking on a closed ball valve?

Water to pump valve is open, and ball valve closed pump goes into bypass to tank

Will not start if I have the choke on, this is with the new carb. I’m going to replace fuel filter tomorrow, also will check the valve clearance.

Can this have anything to do with the pump? I feel like it’s an engine problem.

An engine needs 4 things to run.

  1. compression

  2. fuel

  3. spark

  4. air

Just ideas

Make sure you have fresh fuel in it, also be sure the fuel filter isn’t clogged. On those engines its inside the tank.

Take out the spark plug and make sure its still good and gapped properly.

Check oil level, those engine don’t like low oil levels… It will trip out the oil sensor… Check youtube how to jump it monetary just for testing purposes, it may be going bad…

Oh and one more thing, alot of ppl resort to dropping in new carbs… But if you learn to clean one properly and take it apart there is almost no reason to ever buy a new carb, unless you loose a part or cross thread a needle or something

You ever figure out that hot water machine that was leaking diesel @Chesebro?
Good ole @surfacethearpy just had his leaking as well and it ended up being the thermostat.

1 Like

@Hotshot I did!

She’s on a running like a champ! Loong story! But I never gave up… It really played with me that damn machine

1 Like

Good to hear sir. Happy washing @Chesebro

1 Like

Love hate relationship with that Hydrotek

1 Like

Nice to have you back around again @Hotshot

1 Like

Thank you Jake !

Its been a good machine to you though. They all have there quirks and hiccups soon as you take a pw and make it shoot hot water.

Ill update the thread, I literally just fixed it…

I slapped on a new carb just to get that out my system I was stuck on it having to do with it because off poor winterizing. I felt that maybe I didn’t clean something in the jets or just damaged it.

I put new spark plug in but will check gap spacing today.

Also was mentioned before of maybe over tighten plug, I will bring out the gentle beast today and be more careful.

I have New fuel filter will swap out.

Oil level is good i filled it up to threads and is upto 3/4 of the way up on dip stick. This is where I have alway fill to and ran on, also at first I didn’t go back and put some more oil just in case that was the problem.

Fresh gas was used.

Do you think it can have anything with valve clearance, I was going to also check gap spacing on valve?

If valve clearance was bad, in my experience the motor will try and rip that starter cord right out of your hands like every 3rd try. Overtightening plug can acrually cause your gap to change or close it all together depending on the plug. E3 plugs especially do it to mine.