Kohler CH12.5 OHV engine slow to start

[DarylJ 49]

Have been the owner of a Wheel Horse 312-8 with the OHV engine 12.5 hp since 2002. In the past couple of years, after sitting for a day or longer, the engine requires much longer cranking time to start - in total, perhaps a minute of cranking while choked to start.   When new, choke the engine, crank it, and after a couple seconds it was running. Over time, that crank period has lengthened a bit more each year.  New spark plug makes no difference.  Can this be symptomatic of a fuel pump that is gradually going bad?  Or, is there possibly something else that may gradually be wearing out?  The tractor has under 400 hours from new and has been well maintained.  Can a fuel pump “lose it’s prime” and need to be cranked until re-primed again?  Fuel lines are original, but seem to be in good condition, with no observable cracks.  Any ideas?

[pfrederi 18,639]

Ii isn't the 400 hours is almost 20 years of gas sitting in the pump...the last several probably with ethanol.  Check valves could be bad...Same with the hoses...

Your tractor is too new for me do you have a pulse pump or a mechanical one?

[DarylJ 49]

It’s a mechanical pump, similar to those on the K series engines.  20 years is quite awhile, for sure.  So, could be the pump.  But, I’ve some original pumps on my C series tractors, and they are nearing 50 years old.  OTOH, I’ve replaced several on the K series, too.  Guess their lifespan varies, depending on fuel type and whatever.  Since the fuel pump seems like a logical first place to start, I’ll replace it.  Looks like there are OEM and others that are “for Kohler”.  Not sure if there is any difference in them, as they likely all originate somewhere other than the US.  Will try an OEM, as it’s maybe the best one.

[Handy Don 13,999]

32 minutes ago, DarylJ said:

It’s a mechanical pump, similar to those on the K series engines.  20 years is quite awhile, for sure.  So, could be the pump.  But, I’ve some original pumps on my C series tractors, and they are nearing 50 years old.  OTOH, I’ve replaced several on the K series, too.  Guess their lifespan varies, depending on fuel type and whatever.  Since the fuel pump seems like a logical first place to start, I’ll replace it.  Looks like there are OEM and others that are “for Kohler”.  Not sure if there is any difference in them, as they likely all originate somewhere other than the US.  Will try an OEM, as it’s maybe the best one.

My route was the non-OEM at about ¼ of the price thinking even if I have to replace twice as often I'm still ahead.

 

[bds1984 1,498]

I have the same issue with my 315-8 if it sits for any length of time and it has 450 hours on it.  The usual suspect would be the fuel lines and fuel pump  To start, I'd check the lines and replace them if needed since fuel line is fairly inexpensive.  I've acquired many 312-8s from frustrated owners who didn't even bother checking the fuel lines and the majority of the time that is what it was.  If that doesn't improve, I'd install an inline primer.  I have one on my C165 and it fires right up after giving it a few squeezes after sitting for a month.  If those fixes don't work, then I'd look at the fuel pump, but make sure the original gasket is cleaned off completely.  I once acquired a very clean 312-8 from a frustrated owner who couldn't figure out its starting difficulties.  It turned out the gas smell was from a leaky line between the pump and the carburetor.  The previous owner put a new pump on but greatly disturbed the fuel lines in the process and never replaced them when there were visible cracks.  Another 312-8 came my way shortly after with similar symptoms but wouldn't stay running after a new pump was installed.  This time around the pump had two gaskets on it which was enough to prevent the new pump from being actuated by the cam lobe.  

[DarylJ 49]

Thanks for offering the suggestion about the fuel lines.  Do you have any thoughts on what sort of problems the lines have?  Plugged, cracked to allow air to be sucked into the lines, something else?  The lines on my tractor are still reasonably flexible and do not leak any fuel. No odors or drips or caked on dirt anywhere.  I keep it garaged at all times except when it is used for powering the vac system each autumn for leaf collection.  Otherwise, it sits unused.  Always has Stabil in the tank when being stored, if that helps the life of the lines or not I don’t know.   

 

Once the tractor starts, it runs perfect. Plenty of power, never seems starved for fuel. The primer is a good suggestion, too.  pfrederi’s mention of the check valves becoming defective makes sense.  It reminds me of a well pump that loses it prime. If the check valve doesn’t hold the water from going back into the well, prime is lost.   So, the bulb primer does the priming in the fuel system, just like pouring water into a well pump restores it’s pumping function and the check valve keeps it primed.

Edited October 30, 2021 by DarylJ

[Handy Don 13,999]

 

22 minutes ago, DarylJ said:

pfrederi’s mention of the check valves becoming defective makes sense.  It reminds me of a well pump that loses it prime. If the check valve doesn’t hold the water from going back into the well, prime is lost.   So, the bulb primer does the priming in the fuel system, just like pouring water into a well pump restores it’s pumping function and the check valve keeps it primed.

exactly

[DarylJ 49]

Don, I was going to ask you when you posted the first time….did you have the same problem on your tractor as I am having with mine? If so, did replacing the fuel pump fix the problem?  Thanks.

[pfrederi 18,639]

Might try one of these cheaper than  a new fuel pump

 

 

[Handy Don 13,999]

10 hours ago, DarylJ said:

Don, I was going to ask you when you posted the first time….did you have the same problem on your tractor as I am having with mine? If so, did replacing the fuel pump fix the problem?  Thanks.

I thought so, and yes starting after longer "sits" was easier. In retrospect, though, having read some others' experience, I think a bulb primer would have been sufficient since the pump (and its internal check valves) worked fine once the engine was running.

[DarylJ 49]

3 hours ago, pfrederi said:

Might try one of these cheaper than  a new fuel pump

 

 

 

[DarylJ 49]

Thanks for the link. Ordered one! Definitely a big savings over replacing the fuel pump when all that’s necessary is keeping the fuel in the line from flowing back into the tank.

[DarylJ 49]

3 hours ago, Handy Don said:

I thought so, and yes starting after longer "sits" was easier. In retrospect, though, having read some others' experience, I think a bulb primer would have been sufficient since the pump (and its internal check valves) worked fine once the engine was running.

These pumps seem to have a “failing” mode for an undetermined period of time before they quit functioning altogether, when they become “failed”.  Mine has been failing for the past 3 or 4 years, but I’ve put up with it as it would eventually start the tractor and keep it running as if no problems existed.  If the check valve and primer bulbs overcome the long cranking times, they are definitely an inexpensive solution, at least for awhile.