# Honda GX390 erratic running at full throttle



## legarem (Sep 9, 2017)

I have a honda GX390 on an Ariens 926LE. The motor is near brand new. When I used the snowblower last week, it was working ok but today when I started the motor it was not working smoothlly. At full throttle, the revolution goes high-low-high-low... It is like the tank was getting empty. I see the governor going from one side to the other side. Do you know what could be the problem ? Air filter is dry. Thanks.


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## DriverRider (Nov 20, 2016)

Fuel valve turned all the way on?


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## legarem (Sep 9, 2017)

DriverRider said:


> Fuel valve turned all the way on?


Yes


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## orangputeh (Nov 24, 2016)

it's hunting because it is starving for fuel. most likely the pilot jet got clogged by a little dirt. i would take bowl off after shutting fuel off, drain gas from bowl first from 10mm nut on side of bowl. 

spray carb cleaner up pick up tube and all around.

then take pilot jet out. it is on top side of carb facing out. you have to unscrew that throttle stop screw out first. then gently pry out pilot jet with small screwdriver. clean jet and inspect that small 0-ring on jet. clean the jet out with carb spray and dry with compressed air if you have that. i use a can of air from costco that people use on computer keyboards.

also spray cleaner down hole where pilot jet goes. then put a little oil on o-ring before installing o-ring and make sure it goes all the way in. it should pop back in.

even though it is a new engine, this happens all the time. just takes a microscopic piece of dirt to mess up the carb. maybe from old gas or dirt in gas tank. eyeball the gas tank. you may have to flush out and change fuel filter. 

there are a couple good videos on you tube on doing this for surging or hunting Honda carbs.

this usually works for me. 

good luck and check back.


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## legarem (Sep 9, 2017)

Could it be due to carburetor icing ?


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## drmerdp (Feb 9, 2014)

I’m assuming you used a general purpose gx390. Did you remove the air Filter? Try without. 

Somethings going on with the fuel air mixture. Could also be a clogged jet.


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## vmax29 (Oct 19, 2017)

Is it right after a cold start with rpm surging? Try leaving choke out just a 1/4 way while it warms up. Then cut the choke out all together once it gets under load.


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## orangputeh (Nov 24, 2016)

vmax29 said:


> Is it right after a cold start with rpm surging? Try leaving choke out just a 1/4 way while it warms up. Then cut the choke out all together once it gets under load.


exactly what i should have suggested first. if it will only run right with some choke engaged then the carb needs to be cleaned, especially the jets and the emulsion tube.


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## legarem (Sep 9, 2017)

I started it today. When the motor was warm with the choke used just a little bit, the motor ran smoothly. The standard main jet in a GX390 is a #95 on the Honda HS1332, which have a winterized gx390, they use a #102.


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## vmax29 (Oct 19, 2017)

Sounds like you got it figured out! Good deal.


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## db130 (Feb 16, 2013)

legarem, would you happen to know what the main jet size in a general purpose GX340 versus a winterized GX340?


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## legarem (Sep 9, 2017)

db130 said:


> legarem, would you happen to know what the main jet size in a general purpose GX340 versus a winterized GX340?


As I think there's no Honda snowblowers with GX340, it will be hard to tell you the main jet number needed. I could estimate it and give you a jet number later.


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## legarem (Sep 9, 2017)

Today, I lifted the snowblower on it's bucket and opened the carburator float boal,took out the main jet and blowed compressed air in the emulsion tube in place in the carb. 

Now, motor is running fine but when I open the governor to rev the motor, it doesn'i take it's gas correctly. It sputters. I will have to do a complete carb cleanup.


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## orangputeh (Nov 24, 2016)

legarem said:


> Today, I lifted the snowblower on it's bucket and opened the carburator float boal,took out the main jet and blowed compressed air in the emulsion tube in place in the carb.
> 
> Now, motor is running fine but when I open the governor to rev the motor, it doesn'i take it's gas correctly. It sputters. I will have to do a complete carb cleanup.


sounds like a plan. what does the inside of gas tank look like? if there is a lot of fine dirt in fuel tank, i would take it off and flush, change filter and replace fuel line. 

also, did you put new gas in with some stabilizer and/or seafoam. sometimes you should run it for 20-30 minutes and that will help clean the carb out .


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## leonz (Dec 12, 2014)

If you can find the heavy fabric filter media gasoline filters with the clear plastic housings for small engines they give you much better filtering.


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## legarem (Sep 9, 2017)

As mentionned first, this motor was new so there's no rust or anything old inside the gas tank.


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## db130 (Feb 16, 2013)

legarem said:


> As I think there's no Honda snowblowers with GX340, it will be hard to tell you the main jet number needed. I could estimate it and give you a jet number later.


Actually, there was at least one... the HS1132 TAS.

I looked up the part numbers for the main jets:

34JET, MAIN (#92)
99101-ZH7-0920 

34JET, MAIN (#95)
99101-ZH7-0950

34JET, MAIN (#95)
99101-ZF5-0950

34JET, MAIN (#98)
99101-ZH7-0980

34JET, MAIN (#98)
99101-ZH8-0980

34JET, MAIN (#98)
99101-ZF5-0980


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