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Honda GX390/EM6500 intermittent misfire/backfire causing hunting


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  #1  
Old 04-13-2019, 01:45:11 PM
Rodney Dawn Rodney Dawn is offline
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Default Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Just replaced the rocker arms, and have triple checked they are within spec according to the shop manual, so its not a valve lash issue

new spark plug and fresh clean non ethanol gas 91 octane

cleaned fuel system, changed oil replaced air cleaner and problem persists.

I'mthinking its a carb issue at this point, possibly buildup in internal passages that can't be easily cleaned. Either that, or possibly the ignition system/coil issue.

the generator runs perfect aside from the occasional misfire and hunting that accompanies it. seems more like a fuel starvation problem in that regard. particularly as the problem worsens with load.

occours occasionally while running normal 1750-2100w household loads, but becomes much worse when windows AC kicks on or hair drier in use (spiking watts to 3500w total to start A/C unit or run hairdrier. then settling down to 2700 total draw with A/C unit running.
(The load is evenly distributed half on each 120v leg)

governor kicks in as it should and carries the load, but as the load approaches 50% or so the hunting/intermittent misfire gets worse. it really seems like a fuel problem but wanted to get others' opinions before ordering a replacement carb.
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Old 04-13-2019, 03:12:29 PM
G.M.Johnson G.M.Johnson is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Sounds like ignition system for sure. A quick check for carb problems are black smoke indicating a rich condition. For a quick check to see if it's a lean condition just slowly start adding some choke to richen up the mixture and see if it runs better. Later made Honda's are set to run on the lean side to meet emmessions.
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Old 04-13-2019, 05:23:32 PM
Joe Romas Joe Romas is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

On a Honda surging is a sure sign of a dirty pilot tube. That's the plack plastic part underneath the idle screw. To clean remove the idle screw and gently pry the pilot tube out.
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Old 04-13-2019, 07:45:04 PM
Rodney Dawn Rodney Dawn is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Thanks. That confirms what I was thinking, and thank you for the tip about the pilot tube. I've disassembled several GX Honda carbs for cleaning over the years, and has always assumed the tube was one of those not removable just soak the whole thing in carb cleaner overnight types.Going to try cleaning the pilot tube tomorrow and see if that fixes it. (Cant shut down to do it tonight, as the backup batteries are only at 53% and need to be full so carb and parts can soak for 24 hours if necessary.)
I do have a nice EU3000is I could run to charge batts and run basic needs, (No A/C and fridge simultaneously obviously would have to switch back and forth) as well as various sizes of noisy cast iron briggs gensets and a couple china 2-strokes, so I got plenty of insurance in case I break something trying to get the tube out.

Hardly relevant except in the sense of watts used, but my power system is a hybrid setup gasoline/wind/solar 4000/5000w (4000 continuous /5000 peak rated inverter-charger and 6500w generator total draw never exceeds inverter's surge capacity even when running directly from generator. no microwave, solar hot water, no drier (clothesline) gasoline washer, and oldschool gasoline range with oven (antique coleman lamp and stove co air-o-gas range) coffee maker is old rangetop percolator. LED lighting. biggest loads are the fridge and A/C as well as box fans
heating is a no.5 air-o-gas radiant heater in the living room, and kerosene heaters in other rooms.
well water, but the pump is gasoline, powered by a Honda GX200 engine.
................................

Generator has a LOT of hours on it, but has been well maintained and does not consume any noticeable ammount of oil still pretty much on the full mark at each 96 hour oil change (more convienent than 100 hour intervals. still has great compression and cranks off like when it was new. only issue is the hunting and intermittent misfire that accompanies it.

One thing had me thinking ignition rather than carb issue was because it has never had ethanol or any ethanol-laced blend ran in it and it gets regular use so gumming should not occour, going to try the pilot tube and see if it helpsthough. if not then replacing carb and coil is still cheaper than a new generator.
I did check and clean the muffler and spark arrestor screen to see if carbon buildup was the cause, but it made no difference.
Engine is definately running a little lean, adding choke makes it run smooth and perfect, which suggests a carb issue, however.
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Old 04-13-2019, 10:44:53 PM
turtmaster turtmaster is online now
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

The idle mixture screw with, the cap locktighted on to it, so that you can only turn it a part of a turn, you can easily remove the limiter cap by using old-fashioned soldering gun to heat it up, to soften up the Loctite and pull it off with a needle nose pliers, be careful, so you don't break the head of the screw off Like the service manual says to.

Last edited by turtmaster; 04-13-2019 at 11:37:26 PM.
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Old 04-14-2019, 09:58:18 PM
Rodney Dawn Rodney Dawn is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

managed to get the pilot tube out and soaked everything in carb cleaner for a few hours, and just finished getting it all back together and reinstalled. Problem solved.
hunting issue is nonexistant now even at 50% load.
intermittent misfire/backfire disappeared along with the hunting so it was definately a fuel starvation issue.

Thanks to everyone for the help.

on a side note I've been looking to upgrade as the hour meter has well over 10k hours on it. considering its a 3600rpm machine, that says a lot about Honda quality. anyway the upgrade machine needs to be similar capacity 6500w surge and at least 5000w continuous so I was considering a EU6500 but I dont know if the inverter is pure sine wave or modified sine. does anyone know if its a pure sine wave type?

If its a modified sine wave, then does Honda still make a 6500w surge rated non-inverter type generator, as I need pure sine wave power.

if not then another option would be buying a new GX390 engine and a 6500w northstar generator head and building a DIY machine.
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Old 04-15-2019, 11:04:50 AM
StringJ StringJ is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

The Honda EU6500is is a pure sine wave inverter.

Jerry
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Old 04-15-2019, 05:18:48 PM
Rodney Dawn Rodney Dawn is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Ok, Thank you. I will get the EU6500is then. Fuel efficiency should be a noticeable improvement as well. this tired EM6500 still manages about 4hrs/gal but the EU6500is being an inverter type should do much better than that. I have the EU3000 and it sips fuel compared to the ez3500 it replaced (which I thought was good on gas until I seen how much more economical the EU3000 was.)
(both the EU3000 and the ez3500 it replaced (which still runs/generates) are used for RV/camping).

How is the RFI/em interference on the EU6500is? I'm on 4g and I get a good deal of ignition noise coming over the power cables on the EM6500. (bad resistor in spark plug wire cap, long since ''repaired'' by tinfoil wrap and reinstall method out of necessity. (needed power back couldnt wait for a replacement).
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Old 04-16-2019, 11:57:53 AM
Fred M. Fred M. is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Quote:
Originally Posted by Rodney Dawn View Post
How is the RFI/em interference on the EU6500is?
There is some inverter noise. You may or may not consider it a problem.

My first use of the EU6500is, was for Field Day many years ago. There was noise from the inverter, but a long extension cord helped by keeping it away from our antennas.

I have since found that passing several turns of the extension cord through some large toroid cores cleaned it up.

Fred
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Old 04-16-2019, 03:54:58 PM
Rodney Dawn Rodney Dawn is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Thanks. A bit of inverter noise would probably be easier to manage than the ignition splatter I'm getting now. I've already installed ferrite chokes on the power cords, but the problem is still bad. on battery my 4g signal is -90 dBm and 22.4dB on generator its -107dBm and 13.7dB. (modem located furthest from generator, and using an external Yagi antenna to hone in on the feeble 4g signal that makes it all the way out here.
internet negates the need for broadcast tv reception (android smart tv) but given how much you can hear it on AM/cb radio ( a backup means of communications) I would imagine it would be a big problem for tv reception as well (remember the video part of the tv signal is AM or used to be anyway no idea what the new digital broadcasts are using.)
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Old 04-16-2019, 11:09:03 PM
turtmaster turtmaster is online now
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

FYI, Northstar no longer uses mecc-alte brushless generator heads, now they use brush type generator heads, I'm not too sure of the quality of the new brush style generator heads, they may be good quality, they may be bad quality, I do not know yet.

some may say that all brushless generator heads put out bad quality, dirty power, but the meccalte generator heads do not, I have an oscilloscope waveform "shot" of 10kw mecc-alte, brushless generator head, on a Porter-Cable generator with a Honda GX620 engine.
And the waveform is pretty darn good / clean.
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Old 04-16-2019, 11:40:11 PM
Rodney Dawn Rodney Dawn is offline
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Thanks. I knew mecc-alite heads made good power but i didnt know the generator heads northstar sold were mecc-alites but I knew Northstar generator heads make good power. a 8000w surge/ (6500-7000w cont) generator head would technically be ideal for a gx390, making use of all avalible horsepower with a little breathing room (youll stall the engine before you smoke the generator head). the engine wouldnt have the torque to make full use of the 8000w surge capacity, but the cont duty capacity is what counts anyway, and the extra iron would be a good ''flywheel' when going from light load to moderate load (A/C unit starting up, etc.)
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Old 04-17-2019, 12:23:34 AM
turtmaster turtmaster is online now
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Default Re: Honda GX390/EM6500 intermittent misfire/backfire causing hunting

Northstar had used the Meccalte, generator heads up until about 1 or 2 years ago.
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