Kohler 6.5 fouls plugs after 30 minutes...

My stupid phone logged me out after writing a detailed post...so here’s 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. Didn’t help. It unloaded, then kept surging until it died just seconds later. Wouldn’t 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 wouldn’t refire even hours later. Plugs are probably fouled. Any ideas?

Plugs? So the Gen is gasoline powered?

C lectric said:

Plugs? So the Gen is gasoline powered?

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I guess I didn’t specify but I kinda thought talking about plugs would be enough.

Yes it’s gas.

Dirty fuel and or blocked fuel filters or blocked fuel tank vent

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.

David

Fuel tank vent.

It has NGK’s in there now. I’ll change them and get it running.

I don’t think it’s fuel. It pulls from the right tank, Same one the main pulls from and it doesn’t have any problems.

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.

Involve a genset gas engine expert. PM Ski, he is close by.

describe how the plugs looked.

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.

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

Maybe running too cold. Is there a thermostat?
How about using hotter plugs?

"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.

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/mus/2009/10/The-Lost-Art-of-Choke-Adjustment/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.

A 6 gallon can of fresh gas plugged into the fuel system will help decide the issue.

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.

toni

Hey guys, finally got to the boat since I posted this. Sure enough the generator wouldn’t start. It cranked but wouldn’t fire. So I pulled the plugs and here’s what they looked like. Remember, these are basically new plugs that are fouled.

There’s 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 AC’s. 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. Wouldn’t 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 don’t get why it’s surging. When I put resistance on the throttle linkage, it sounded fine.

Once it warmed up, it was smooth. That’s when I had my wife turn on the AC while I recorded. It actually startled me. Doesn’t sound happy under that load.

Anyway, I sprayed carb cleaner into an vacuum hose and also into the carb while running, but it didn’t seem to help. To me, the systems seem to work, just acting like the carb needs to be cleaned.

What do you guys think? I’m 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

How's the governor spring??

Art said:

How's the governor spring??

Click to expand...

See the videos? Looks like it’s there, that’s about all I know.

Steve91T said:

See the videos? Looks like it’s there, that’s about all I know.

Click to expand...

Steve

Check out if you can find new governor spring. Best to get OEM or aftermarket clone if possible... due to the exact tension needed. Governor spring helps maintain correct rpm and resulting hertz. They can get weak over time and no longer hold throttle at correct level. What make, model and year gen set is it? Very simple fix if that is reason for yours running poorly.

Best luck!

Art

What`s that drip in the top right of both videos?

Those plugs don't look like the problem. I'm sticking with fuel starvation.
Does the gen exhaust have any smoke when surging?

Plugs look good. Might even be a touch lean. And engine sounds good.

What the heck is dripping on unit? Looks like water dripping right on the carb!!

Main gov spring looks ok. Little tension spring on actual throttle linkage is broken, that one keeps slack in linkage taken up in one direction to increase stability. What you have is governor instability.

Choke is working fine.

Throttle stop (basically idle screw, but not on this app) should be set so at no load warmed up, throttle is almost bumping the stop. This helps in stability.

There is an idle mixture adjusting screw that can play into stability, try adjusting that a turn in or turn out.

Any friction on throttle mechanism hurts stability, a touch of lube on all moving parts can help.

I'd still go through the carb. Water dripping on carb may have throttle plate shaft sticking.

Gas gennie carb/governors are a PITA. Lots of things have to be perfect for them to run right. They drive me nuts.

Hey guys. Thanks for the responses. The drop is from my fresh water shower hose. It drips a little when the system is pressurized. It normally drips onto the cover and then runs down, but obviously I had it slid back to get to the carb and plugs. Trust me, it’s on the list.

I know the plugs looked good, but they were fouled.

When it’s running well, there’s no smoke. When it starts to foul the plugs, surge and bog, it’ll smoke and I can smell rich exhaust.

Once it dies, sometimes I get can get it to retire after some time, like I did in that first video. But sometimes it won’t fire at all, even months later. When I got to the boat a few days ago, I tried to start it and it wouldn’t fire. I pulled the plugs (pic I posted) and they smelled like gas.

I feel like it’s running like my old weed eater. Would start right up but would bog like crazy if I gave it too much throttle and load.

The throttle and choke levers move very smoothly.

One thing I will add, so I changed the plugs and then headed to the airshow. Once there, it started and ran great, powering everything but the ac’s. It was smooth and super quiet. Almost couldn’t hear it. We were impressed. 30 minutes later I shut it down. Fast forward and hour and a half and I start it up. This time it was surging and bogging. I put a small load on the trying to clear it up and it was just getting worse. I shut it down before it died. Then I restarted it and it was worse than before. Then I started it again and took a video yet it didn’t last more than 5 seconds before bogging and dying. Then it wouldn’t refire at all until the next day when I took that video of it.

So back to the weed eater. What causes a small carbbed engine to bog when you give it full power? Probably not enough fuel due to a clogged jet or something.

I had a 40 cc 4 stroke dirt bike a few years ago that ran great, just had a bog when I opened the throttle. I took the carb apart and found the accelerator circuit completely try. There was a tiny piece of trash clogging the circuit. Cleaned it out and it fixed the problem.

I bet the carb needs to come apart. Anyone know what special tools required? Maybe an Allen wrench set along with a standard set of tools?

So what is the exact model number?
Otherwise we are all just guessing.

High Wire said:

So what is the exact model number?
Otherwise we are all just guessing.

Click to expand...

I should have looked while I was there. It’s a Kohker 7.5 (I put 6.5 in the title by accident). The boat is a 1996, I think it’s safe to assume it’s original. I might go back down to the boat tomorrow to work on the generator.

Surging can be a dirty carb, the fuel flow is insufficient to the jets. Then it bogs, as it slows there is less demand and the fuel fills up again to the jets.

Typically if its a carb problem, if you hold the throttle steady so it can not move, it dies.
Is the main jet adjustable? If so open it up a little.

Surging can be a governor spring not placed in the right position in its linkages.

I would take apart the carb and clean it, you can soak it in white vinegar, rinse with water and blow out all passages with compressed air.

ARE you USING fuel stabilizer?? If not, then you should.
Gasoline today is terrible quality, having ethanol, it grows acetobacter, which makes vinegar and gums up the fuel and corrodes the metals. There is always some water dispersed in gasoline and the bacteria live in that water and consume the fuel. One thing fuel stabilizer does, it prevents the growth and the corrosion.

These old style carbs are open to the atmosphere along with the tank vent.
Your car does not have these issues as its most of the time sealed from the humid air. And much of the fuel system is plastic. Your car has a fuel system with a 2 way sealed tank fill cap, it can vent in and out but most of the time the valve stays shut, so the fuel stays good a long time. And at the engine, the injector tip is shut. A carb is always exposed to the humid air.

I use this Marine Stabil, in the larger bottle. My fuel system corrosion issues ceased.
https://www.walmart.com/ip/STA-BIL-...75035&wl11=online&wl12=16645041&wl13=&veh=sem

What specifically have you really checked other than trying to run it periodically?

What kind of gas are you running it on? Octane? Ethylene?
Model number?
Do you have a manual? If not then you should arrange to get one.

We can keep throwing suggestions but it won't help if you only are trying to run it.

Fouled, sooty plugs are are usually too much fuel. As mentioned a faulty choke is often a cause but have you checked it for proper operation. Have you confirmed that the choke is actually operating? The levers may be free but the choke can still goof up.

Have you tried a cleaner such as SeaFoam?
Have you tried running the machine from a clean source of fuel such as a 1 or 2 gallon fuel jug?

There have been many similar reports over the years. New plugs often fix the problem so i doubt it is governor etc. if one cylinder gets fouled I would expect it to start of but not handle a load. I would try a higher heat range plug set after making sure the ignition is in good shape. I assume it runs on the same gas as the mains so that is probably not the issue.