GX390 Honda engine (in a generator)

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  #1  
Old 02-16-15, 03:29 PM
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GX390 Honda engine (in a generator)

I have a generator with a *new* GX390 engine. The engine is surging at idle and I can see the governor arm going back and forth; this behavior disappears when I put a decent load on it. It is a 6500W generator, the surging disappears at about 2000W worth of load.

With the choke pulled out about 1/3 of the way the engine runs smoothly.

I googled a bit, and the suggestion that comes up most often is to clean the carburetor. What's confusing is that the generator is new, filled with gas about a week ago for the first time.

Any ideas? Thanks. It is still under warranty, and I could replace it in Costco, but it is so heavy that I'd rather not haul it anywhere if I could help it.
 

Last edited by kotton; 02-16-15 at 04:01 PM.
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Old 02-16-15, 04:36 PM
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All it takes is one batch of old or dirty fuel to clog or gunk up the carburetor. It's also possible that your carburetor needs adjusting or is otherwise defective. Unusual for a GX series engine but it is possible.
 
  #3  
Old 02-16-15, 05:08 PM
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Too bad. Now I wonder what would be easier -- hault it back to the store (would have to rent a truck) or try to clean the carb -- I've never done that before.
 
  #4  
Old 02-16-15, 08:45 PM
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Feeling a bit more adventurous about this and will try to clean the carburetor; but thinking first, could it be that the idle fuel mix ratio was not set correctly at the factory? Is there a screw that controls the mix at idle speed on GX390, and does it make sense to tinker with it? Thanks.
 
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Old 02-16-15, 08:49 PM
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Yes... it sounds like the carb is set a little on the lean side which would cause that surge problem.
 
  #6  
Old 03-07-15, 11:03 AM
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I finally took apart and cleaned the carburetor. I also had to adjust the idle screw about 1/4 of the turn (as far as the limiter would allow). I replaced the broken gasket on the air filter side. The engine is now very stable at idle, but for some reason started surging at about 1/4-1/3 of the load. I am quite sure the main jet is clean now. Any guess what could be wrong?

Thanks.
 
  #7  
Old 03-07-15, 02:00 PM
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It's still something a bit clogged in the carb. I doubt you could take it back for warranty since warranty doesn't cover that sort of problem (gas left in it long enough to cause a problem is not a defect in manufacture). Did you take out the jet under the idle screw and clean it?
 
  #8  
Old 03-07-15, 03:38 PM
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You are right -- I called for warranty a couple of weeks ago, and was told this was a maintenance issue; plus I would have to haul 120 pounds to the dealer in a Civic I'll try to clean the carburetor again and report back. I did take the idle screw and the needle out.
 
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Old 03-07-15, 06:08 PM
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The jet that is located under the idle screw. It's plastic and has to be pulled out. Did you take it out and clean it?
 
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Old 03-07-15, 06:45 PM
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Just to make sure we are talking about the same thing, this is the small idle screw with the spring on it and a limiter cap on top of it, correct? I don't think it had anything plastic underneath it. I took the screw out, it had a long sharp tip, all metal, that goes into the nozzle located in front of the throttle. What I had is shown on this video: https://www.youtube.com/watch?v=h0lUuuSCA2A, at 5:23. This carburetor might have a different configuration from what you had in mind? Thanks.
 
  #11  
Old 03-08-15, 12:24 PM
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That's the mixture screw. The idle screw is plastic. The jet under it is also plastic. I fast forwarded that video to see if they showed the jet and they do at about 3:25.
 
  #12  
Old 03-08-15, 01:05 PM
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Got it, thank you. What function does it serve?

I am happy to report that after cleaning the carburetor again (and the idle screw/jet) the engine runs like a clock, stable at idle and load. Thanks much for all the help!
 
  #13  
Old 03-08-15, 07:42 PM
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It supplies fuel at rpms lower than full throttle. It's very often the problem when these engines surge.
 
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