How To Adjust The RPM On A Honda GX390 Generator Engine



In this video I show you how to adjust the engine speed (RPM) on a Honda GX390 generator engine. Usually 3600 RPM is a good engine speed for your generator.
Always check with your manufacturer for correct engine RPM setting.

I bought the tach here http://www.jbtoolsales.com/electronic-specialties-328-ez-tach-plus-0-20-000-rpm-tachometer/

Due to factors beyond the control of DONYBOY73 “The Small Engine Doctor”, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. DONYBOY73 “The Small Engine Doctor” assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. DONYBOY73 “The Small Engine Doctor” recommends safe practices when working with power tools, hand tools, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of DONYBOY73 “The Small Engine Doctor”, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not DONYBOY73 “The Small Engine Doctor”.

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40 thoughts on “How To Adjust The RPM On A Honda GX390 Generator Engine

  1. this maybe a dumb question, but would it not be better for the motor if they had the motor running at 1800 rpm with a gear ratio to run the generator part at 3600rpm ….. seems like it would be alot quieter and better for the motor if they designed it this way ?? Im sure they dont want motors to run for 30-40 yrs like the old briggs flatheads could …… or have I over thought this ?

  2. You can also plug a frequency meter into one of the power outlets and adjust the engine speed for a reading of 60 hertz (USA line frequency 60 cycles/ second = 3600 cycles/ minute hence 3600 engine RPM). Some generators have a frequency meter built in or you can use a device like a P3International Kil-A-Watt available from many sources. I like to adjust my generator for 60 Hz while the generator is supplying about a 50% load. As the load increases, the frequency will decrease a bit as the engine slows down and as the load lightens, the frequency will increase. My generator does not have closed loop frequency control, so setting the line frequency (engine speed) with a typical load is a reasonable compromise.

  3. Honda clones redline at 3600 yet mine has seized up t 3000 rpms. Pulled the head and no damage, cross hatches are perfect. Will not turn by rope or starter. Think a bearing spun?

  4. Thanks great video. I needed to clean carb but seen they were cheep so I just replaced it. It started easy but the RPMs are way to fast now. Looks like the gov linkage isn't moving over to slow it down unless I hold it over by hand. Is this what I should adjust for this or do I need to look into the gov?? Thanks It worked fine the last time I ran it.

  5. Can you check the RPM on a honda ex-5000 with the old type auto style tachometer, that has two wire clamps? Where would you connect the clamps on the generator? I am a new subscriber, THANKS FRIEND.

  6. First off: That looks awfully Chinese-made to me….or are the Chinese cloning better these days?

    Anyway; You failed to mention just how the governor works or even the effect of the plastic throttle stop screw on the carb.
    Also, the revs will be affected by the setting of the air/fuel mixture screw….a metal screw on the side of the carb.
    (Be guided by the plug colour).

    The idea of the governor is to speed UP the engine when a heavy electrial load is placed upon it…..it then throttles back as the load is catered for, that is, as the running amps diminish…..
    It is the shock of the heavy amperage start up, that the generator tries to cope with.
    ( A heavy duty 9" angle grinder for example.)

    What should happen is as the revs fall, the windage on the governor (Within the generator) is decreased & that causes the lever to pull the throttle open…when the windage returns to its normal level…ie the revs have now increased…it SLOWS the engine & maintains the RPM at the correct voltage. (The higher the RPM….The higher the voltage [& Hz incidentally.)

    The same Governing action is used on Briggs & Stratton engines…lawnmowers, for example….You hit a patch of, say, damp grass & the load on the blades is increased…the revs fall….the windage falls & the thottle is pulled open to increase the revs & thereby the energy to cut the wet grass or whatever…..before the engine stalls. Sounds so simple! Yet can& does go wrong.

    HEY!!!!
    Not trying to be clever here…or criticize the poster…..but there is somewhat more to getting the revs right than that one single screw……

    I have a similar generator in at the moment: It runs perfectly well at 220v/50Hz (South America) but when faced with a shock load, the RPM & voltage falls & the governor is not compensating for it by increasing the revs…..as the grinder runs, the current demand falls & the Genny revs return to normal…….
    But then, load the Grinder with some actual work, which increases the amperage load…. & you find your self in a vicious circle…..

    I came here looking for a solution but the nearest I could find was this example….and sadly, it does not really help.

    I'm sure someone out there will say: "Ha…this is what you do…..!"

    (BE AWARE: With some clones of the HONDA ENGINE….
    Running them at maximum speed can cause self-destruction of the engine…..Seriously.
    What happens is that the magnet ON the flywheel (that provides the ignition spark) can become "displaced" & rips the induction coil off its aluminium mountings.
    I've had two machines in, that lost that permanent magnet off the flywheel:
    One I salvaged with a new Flywheel…[not cheap either.]

    The other demolished the Coil Mounting lugs….Engine is scrap……
    What some clever clogs did, was manually hold the throttle wide open when switching on the massive electrical load which was stalling the engine….A BIG NO-NO!..))

  7. I have a generator with the same honda motor. I have to keep the choke pulled out at all times or the motor dies. Do you have a suggestion on whats wrong?

  8. I have a generator with the GX390 engine. when I run it and have something running off from it, it surges. The only way to stop the surging is to pull the choke out about half  way. What can I do to stop the surging?

  9. I have a Honda gx390 motor with a comet zwd4040 4000 psi pump on it. When I pull the pressure wand trigger, the rpm is normal, but when I let go of the trigger the rpm goes way up. What do you think I should do? Will the rpm screw work on the pressure washer?

  10. I just bought the EX Tack Plus like you have in the video. I also have the same Honda GX390 engine on my generator.
    Did the readings on your tack jump all over the place. It seems you have a steady readout. The one I have right out of the box, the readings are all over the place (2,473 rpm to 3898rpm) I have an analog wireless tack that reads steady at about 3800 which is about right for a miller generator. I noticed that your reading was steady at 3600rpm. Maybe I got a bad meter.
    No way I can adjust accurately with readings jumping all over. I used the setting 2:1 with the cable and wireless same results.

  11. i have a Chinese gen with a clone of a gx200 on it.  the governer is real touchy but I have it set between 3500 and 3600RPM but since its mechanical it will occasionally wander above by 30-40 RPM's.  on generators like this that have a automatic voltage regulator the rpm's aren't as important as on one without.  if your just running light bulbs or power tools or things like air conditioners the lower frequency shouldn't bother anything.

  12. Donyboy – I had one of these generators and the gas tank was so corroded, it looked like they ran red mud in it. I let vinegar sit in it and some sea foam and gas. Plus took a flexible magnet tied rags to the end and cleaned inside with about 40 rags. It was pretty clean unless you let fuel sit in it, it would clog back up. It was hard to even get all the gas out of the top and bottom holes

    Is there a good way to clean one of these tanks out?

  13. my genorator has a gx390 and it runs at 2000 rom's. that is what themanufacturer reccommends and it pumps out 130 volts. i really like it, it is nice and quiet. the arc welder with the same engine runs at 4k rpm's and it is really loud, you can't hear the weld so it is really hard to weld with it

  14. Thx for the Vid Donny. I have a question regarding how/where you obtained your tach reading from. I purchased a digital tach myself but a different brand name. So my question is, what are you pointing the laser at to get your RPM reading?

  15. I have a Subaru generator with a Robin engine. The intake air filter (279-32612-08) is deteriorated, a simple air filter is $25. Any alternative suggestions ?  

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