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Discussion Starter #1
Have a 26.5 HP Koehler EFI on my Batco conveyor, has been giving me troubles lately. It run good idling and at top RPM.
Once you load it the RPMs drop fast to the point the engine could stall out. I would say I’m lucky to run it half what it should.
I had a tech come out and look at it, found out the oxygen sensor wasn’t working. This sensor has failed once before. Put new one in thinking this would solve the problem .... didn’t help one bit. We are now thinking there is something wrong internally in the engine.
Anyone else have an issue like this?
Thx for any help.
 

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Discussion Starter #3
I’m not sure. He checked the compression, everything was fine there.
Thx for your thoughts, will ask the tech.
 

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I've had numerous Kohlers with mice eating wiring harness. Causing either no operation, intermittent operation, or numerous other symptoms seeming like fuel. Mice like Kohler wiring, something in it that attracts them. Would double check that too.
 

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I’m running my efi without the sensor, working good so far. I’ll second that mice love to get into the Kohler motors. We stuffed a lot of wire wool around the engine to mouse proof it.
 

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There has been more threads on poor engine performance of Koehler engines than all the rest combined.
I had a bleeding edge EFI water cooled 31 hp Koehler in 08, It ran great for about three years then started to skid to as described to the performance others have had.
About the time I may have solved the expensive puzzle I no longer used the auger.
But the last time used performance was below what it was in it’s early life.
I gave up.
 

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Had same issue as you last fall when I went to seed ww I use mine to fill my drill. For some reason I took gas cap off and it worked fine. The vent on the cap was plugged was all it was. Hopefully your as lucky as I was and maybe that’s all it is.
 

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Discussion Starter #8
Had same issue as you last fall when I went to seed ww I use mine to fill my drill. For some reason I took gas cap off and it worked fine. The vent on the cap was plugged was all it was. Hopefully your as lucky as I was and maybe that’s all it is.
I won’t have as good luck as that. 😂😂
Thx for the thought will check it out. Be a nice cheap fix if that was it.
 

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EFI without the sensor isn't really the best. Similar to not running it in a vehicle. Best bet is to run better fuel. One of my local dealers has found that the dyed gas causes problems. We used to run premium but have recently switched to using dyed gas again but with ProLab additive since we have heard positive results.
 

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EFI without the sensor isn't really the best. Similar to not running it in a vehicle. Best bet is to run better fuel. One of my local dealers has found that the dyed gas causes problems. We used to run premium but have recently switched to using dyed gas again but with ProLab additive since we have heard positive results.
I use 1/2 regular, and 1/2 AV gas. These engines need high octain.
 

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I have a Brant belt with the Koehler carb. That dam thing runs the shits if the battery is low. Put the charger on runs grate. I know this is stupid but true.
 

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When you said av gas, that has me wondering if one or more components has been compromised from the av gas. Av gas isn't just gas with a higher octane, it has components in there that will really degrade any typical rubber fuel line for example and not sure what other items it will harm. So for example the fuel hose after the filter starting to flake off bits of rubber and gone into the fuel injectors or the fuel pump itself not compatible with that fuel.

I don't mean to give you a heart attack over this !, but its something to be made aware of and a friend of mine was using av gas in a higher compression older car he has and at first it was great but it didn't take long and it wasn't so great as he was having crap come into the carb and part of that would have been rubber particles.
 

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When you said av gas, that has me wondering if one or more components has been compromised from the av gas. Av gas isn't just gas with a higher octane, it has components in there that will really degrade any typical rubber fuel line for example and not sure what other items it will harm. So for example the fuel hose after the filter starting to flake off bits of rubber and gone into the fuel injectors or the fuel pump itself not compatible with that fuel.

I don't mean to give you a heart attack over this !, but its something to be made aware of and a friend of mine was using av gas in a higher compression older car he has and at first it was great but it didn't take long and it wasn't so great as he was having crap come into the carb and part of that would have been rubber particles.
I think you have this backwards. if an airplane model qualifies for a mogas stc ( 92%+ automotive fuel) the stc requires rubber hoses Orings and gaskets are compatible for auto fuel as some components in auto fuel will disintegrate rubber. It might be the lead in the 100ll aviation fuel causing a problem with the ox sensor.
there is also a product called Decalin that you can add to 100ll to prevent the lead in the fuel from sticking to valves pistons etc. 1oz treats 20 gallons. It might help with the oxygen sensor.
 

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I think you have this backwards. if an airplane model qualifies for a mogas stc ( 92%+ automotive fuel) the stc requires rubber hoses Orings and gaskets are compatible for auto fuel as some components in auto fuel will disintegrate rubber. It might be the lead in the 100ll aviation fuel causing a problem with the ox sensor.
there is also a product called Decalin that you can add to 100ll to prevent the lead in the fuel from sticking to valves pistons etc. 1oz treats 20 gallons. It might help with the oxygen sensor.
I hear you as to airplane components being compatible with regular fuel although there a lot more to it as to automotive gas does not have the qualities of av gas when it comes to altitude and vapor lock and auto fuel with ethanol is a killer to the carb components. But back to the av gas and rubber components, I had a chat with a rep of a well known hose manufacturer and he knew his products and he nearly flipped out when I told him of a local well known hose dealer who was recommending a certain fuel hose for use on a bulk av gas storage tank. He said they make a fuel hose certified for "before" the fuel filter on a bulk storage tank but definitely not after. Its a very special hose that only a couple of manufacturers make that we can get here. What he said is that normal hose starts to fall apart and flake off and that is exactly what I was having happen ( yes I saw that with my own eyes and was a very unsettling discovery ) and he referred me to an aircraft fuel hardware supply company where I was able to order up the correct hose and Continental is one of those brands ( like they use at all airports ) and the correct type of fuel filter.

But you mentioned something as well I wasn't even thinking of, yes the lead in the av gas !. I can see how that would not be kind to a sensor and no matter the engine it would eventually cause issues if its got an ox sensor.
 

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Do you have a filter on your 100LL tank as it would be interesting to run some fuel into one of those 5 liter clear plastic pour containers ( a clean one of course ) after the fuel has sat in the hose for some days so another words not flushed out if there were particles coming off of it. Then filling a container like that you would see if there were any black specs floating around in the fuel or settling to the bottom and if there is a filter at the tank, you would know its coming from the hose itself. That would be a bit of a feeler to see what if any crap you've had flowing through and you can go from there with how urgent it is to do something about it. Its been a few years since the discovery that took place of finding the black bits in the fuel and initially I thought the fuel filter was at fault and since it was an obsolete unit I bought the proper filter assembly specifically for av gas. But it was the hose all right, I cut it off at the nozzle and could stick my finger into the hose and wipe black particles off the hose, yeah that was the Holy Sh-it moment !. The filter I have is a water absorbing unit and is 0.5 micron, yes you read that right as its half a micron rather then a typical 5 or 10 micron filter one would be using for gas or diesel. But none of that does any good if the hose is falling apart down stream from the filter !.
 

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Junk motors they build these days are frustrating. We have an old 13 hp briggs on a antique 6" auger. Back in the day the motor had a place you could wind the rope. That thing started so good I remember as a kid just grabbing the belt and pulling it 6" and the thing would take off loaded. Good old mag ignition. That thing never gave a problem ever. My grandpa bought that auger used and it had a hard life with mineral oils of the day etc and a bad maintenance schedule. Things were just expected to work back then and were built to.
 

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Found the problem ...... burnt exhaust valve.
That's interesting, so the tech checks the compression and claimed it was good and yet the exhaust valve is burned badly enough to affect the way the engine ran. I wonder what the root cause of the valve being burned is, if it ran lean at some point, or a valve train issue that isn't allowing it to quite close.
 
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