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Old 01-12-2018, 09:37 PM   #1
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Kohler 6.5 fouls plugs after 30 minutes...

My stupid phone logged me out after writing a detailed post...so hereís the shortened round 2 version.

The PO of our boat never ran the generator. We have owned it for 6 months and I got it running after changing the plugs.

I run it under a load every time we at the Boat. It starts and runs great every time. We even ran it for about 12 hrs just 2 months ago. The other day we ran it under load and after about 30 minutes it started to surge. Hearing it struggle, I leaped into action and killed the heat unloading the generator. Didnít help. It unloaded, then kept surging until it died just seconds later. Wouldnít refire. About 45 minutes later it fired back up and held a load.

The next day while in the slip I fired it back up and ran it under load trying to see if it would do it again. Once again it ran great until about 30 minutes, then started surging and died. This time it wouldnít refire even hours later. Plugs are probably fouled. Any ideas?
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Old 01-12-2018, 09:51 PM   #2
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Plugs? So the Gen is gasoline powered?
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Old 01-12-2018, 09:57 PM   #3
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Plugs? So the Gen is gasoline powered?
I guess I didnít specify but I kinda thought talking about plugs would be enough.

Yes itís gas.
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Old 01-13-2018, 04:07 AM   #4
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Dirty fuel and or blocked fuel filters or blocked fuel tank vent
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Old 01-13-2018, 06:32 AM   #5
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I would change the plugs and give it another try. I had a cheap Chinese made brand new gas generator and the plugs failed (but didn't look fouled) within hours. Replaced it with Champions and it ran fine afterwards.

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Old 01-13-2018, 07:15 AM   #6
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Fuel tank vent.
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Old 01-13-2018, 08:12 AM   #7
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It has NGKís in there now. Iíll change them and get it running.

I donít think itís fuel. It pulls from the right tank, Same one the main pulls from and it doesnít have any problems.
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Old 01-13-2018, 09:04 AM   #8
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Its not the fuel. Any restriction in the fuel would cause it to run lean. Its either running rich OR the spark is weak. Since it starts easily and fouls the plugs in 30 minutes its much more likely its running rich. Either not enough air or too much gas. Check the air filter/air intake to make sure there are no restrictions. If that's ok, you need to carefully check the carb. Could be a leaking float valve, "fuel logged" float or perhaps the choke or enriching circuit is not working properly. I don't think a restriction in the exhaust would do this, but maybe. If all else checks out you may want to verify that the exhaust is clear.
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Old 01-13-2018, 09:12 AM   #9
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Involve a genset gas engine expert. PM Ski, he is close by.
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Old 01-13-2018, 09:19 AM   #10
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describe how the plugs looked.
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Old 01-13-2018, 09:40 AM   #11
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Post pics of the plug firing tips.

Check that choke is not hung up and put a new air filter in.

May need to go through carb.

I had one here that did the same thing. I went through the carb. Still ran rich and fouled plugs. Bought a new carb (was not too expensive) and that one ran rich too!! Could not imagine any fault in the engine that could explain it, so ordered some leaner main jets from a motorcycle website. Bought like four in progressively smaller sizes and tried them til it ran right. One seemed perfect. Been running great in the like four years since.

You can tell it is running rich by the smell of the exhaust. May even see soot in the smoke. Rich running makes an acrid stink. Correct mixture and almost no stink. Hard to describe, but my schnozz is calibrated for evaluating deviation from stoichiometric combustion.

This is the Kohler with the Honda in line two cylinder. 6.5CZ I think.
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Old 01-13-2018, 10:53 AM   #12
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My suggestion is to check the automatic choke. Sometimes the shaft on the butterfly valve (the valve that blocks air flow into the carburetor) suffers from corrosion at the pivot points causing the valve to either not open at all or not all the way. I have had to lube mine several times on my Kohler 7.5KW
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Old 01-13-2018, 12:47 PM   #13
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Maybe running too cold. Is there a thermostat?
How about using hotter plugs?
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Old 01-13-2018, 03:53 PM   #14
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"Plugs are probably fouled..." ??? Doubt it. Fouling doesn't come and go.
Surging = Fuel starvation. Find out why. Kinked hose, blockage, blocked vent, clogged filters, sticking float, clogged jets.
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Old 01-13-2018, 09:14 PM   #15
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I guessed gasoline but rather than blather on I figured I would ask to be sure.
I don't know your machine so this is more guessing.

If the plugs were fouled, sooty black, then as mentioned already maybe the choke is not working properly. They do hang up. Sometimes a CHOKE cleaner spray can help. Otherwise it may need dismantling to clean or some new parts.

Below is a description of an electric choke operation and an automatic mechanical one afterwards rather than me writing it as it's been long enough since the last time I played with one I'll will be hazy.

How does an electric choke work? - Hot Rod Forum : Hotrodders Bulletin Board

Check the connection. If power doesn't reach the coil it won't work.

https://www.hemmings.com/magazine/mu...t/2144991.html

The actual temp sensing of the mechanical ones can be different but again they can gum up and fail to open properly.

If either fails to open reliably the result will be a very rich mixture which will foul the plugs. That rich mix is needed when the engine is dead cold but is not needed once the engine warms.

Check the choke operation for free operation, from not being gummed up, and the adjustment as that too can goof things up if it has moved.




Surging though is usually fuel starvation caused by a plugged jet. Some times that can be cleared with the use of something like SeaFoam but only if the jet has not completely closed. If it completely closed then the carb may need a strip down and cleaning with a GOOD cleaner.


The decent operation initially may be from the choke operating correctly, creating a very rich mix, but as the engine warmed and no longer needed the choke and it backed off the mix became too lean which caused the surging.
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Old 01-14-2018, 06:34 AM   #16
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A 6 gallon can of fresh gas plugged into the fuel system will help decide the issue.
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Old 01-14-2018, 12:19 PM   #17
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not sure of your particular engine, but I've messed with quite a few of those on old motor homes. if all else fails, the carb is easy to rebuild BUT, there are some tiny jets/openings in their and you really have to find them and make certain they are clean. If those foul, the carb can look great but perform poorly; exactly as you are describing it.

also, depending on the choke set up, if its mecchanical, the butterfly can open and close as the engine starts surging, making it worse. to check that, you can manually leave it open after its warm and you'll know right away.

good luck. It should not be too hard to figure out.

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Old 04-30-2018, 11:37 PM   #18
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Hey guys, finally got to the boat since I posted this. Sure enough the generator wouldnít start. It cranked but wouldnít fire. So I pulled the plugs and hereís what they looked like. Remember, these are basically new plugs that are fouled.

Thereís a pic of the plugs as I pulled them out. I replaced them and the generator fired right up and sounded great.

So we boat to the Myrtle Beach Air Show and throw the anchor. My wife need the gen for about 30 minutes. It fired right up and sounded great. Smooth and quiet. It was running everything but the ACís. When I did turn one on just to try it, it started surging. Anyway. It ran great for 30 minutes then I shut it down. And yes, I did allow a couple of minutes for warm up and cool down with no load. Anyway, after the show we boat 1.5 hrs to a restaurant. I fired up the generator. It ran poorly for all of 6 seconds and quit. Wouldnít fire. Plugs were fouled. Crap.

Fast forward to this morning (the very next day). I pulled the cover back and recorded while I tried to start. It was ugly, but it started. I donít get why itís surging. When I put resistance on the throttle linkage, it sounded fine.

Once it warmed up, it was smooth. Thatís when I had my wife turn on the AC while I recorded. It actually startled me. Doesnít sound happy under that load.

Anyway, I sprayed carb cleaner into an vacuum hose and also into the carb while running, but it didnít seem to help. To me, the systems seem to work, just acting like the carb needs to be cleaned.

What do you guys think? Iím going to take a solo trip to fix this gen because later this month we are moving from Myrtle to Wilmington with a 4 yr old and a newborn. We need this thing working.

Thanks guys!


https://youtu.be/UZ7KzOTlXHc

https://youtu.be/KjFvYii1VCg
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Old 05-01-2018, 12:09 AM   #19
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How's the governor spring??
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Old 05-01-2018, 12:23 AM   #20
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How's the governor spring??
See the videos? Looks like itís there, thatís about all I know.
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