Kohler Magnum 16hp runs great and then dies

[Fescuefreak]

Could use some help. I have an old Walker mower with Kohler Magnum 16 hp that runs great for about 10-15 minutes then starts surging like it is running out of fuel and will backfire as well. If I play with the choke I can limp it along but eventually it dies.
Things I have already done:
1. Replaced the carburetor including new spacer and gaskets
2. Replaced fuel lines just after filter and just after fuel pump (maybe should change fuel line between tank and filter?)
3. Replaced fuel filter
3. Cleaned spark plug and check for spark after engine dies and spark is there
4. Checked and adjusted rpm to 3200 (was previously set to max out at 2700 - pretty far below spec)
5. Replaced batter
6. Replaced voltage regulator/rectifier

These symptoms occur with or without air filter attached and do seem worse or occur more quickly when under load (blades engaged).

After I replaced the carburetor and carb gaskets which were in terrible condition the engine did run a full hour and I completed the mow and thought I had fixed the issue. Then I decided to check the rpm’s and found them to be low at 2700 so adjusted it to 3200 (engine max is 3600) but the symptoms reoccurred during the next mow.

What should I be looking at next? I feel like when the engine gets hot it must be getting too much air in the mixture possibly? Or lack of fuel somehow? Not sure if this old engine even has a safety switch for overheating but I don’t think adjusting the choke would keep the engine alive if that were the issue.

Help appreciated!

 

[Rivets]

Next time it happens spray everything you can find with carb cleaner, between carb and block. You are looking for an air leak by the gaskets or a crack in the intake manifold opening as it heats up. Also check for debris floating around in the tank.

 

[kyledeere79]

You should test for a blocked air vent in the gas cap by running your engine til it dies then loosen the cap and listen for air being sucked in. If you do hear the noise of air that means the vent is blocked and causing a vacuum.
The other test I would do is disconnect the fuel line at the carb and crank the engine. Gas should spray out and not just trickle. Obviously don't do that test with a hot engine. If you do need a fuel pump, I recommend getting one from stens or kohler rather than Amaz. The cheapest ones are pretty bad

 

[Fescuefreak]

Next time it happens spray everything you can find with carb cleaner, between carb and block. You are looking for an air leak by the gaskets or a crack in the intake manifold opening as it heats up. Also check for debris floating around in the tank.

Thanks. Will try that. Also, the spacer I installed already had the gaskets attached to the spacer, I did not use any adhesive or anything, just tightened the carb to the intake - is this correct or does something need to be applied to create a better seal?

 

[Fescuefreak]

You should test for a blocked air vent in the gas cap by running your engine til it dies then loosen the cap and listen for air being sucked in. If you do hear the noise of air that means the vent is blocked and causing a vacuum.
The other test I would do is disconnect the fuel line at the carb and crank the engine. Gas should spray out and not just trickle. Obviously don't do that test with a hot engine. If you do need a fuel pump, I recommend getting one from stens or kohler rather than Amaz. The cheapest ones are pretty bad

Thanks. I have made sure the gas cap vents… I can push air through it with my mouth so that part is good. I will try testing the fuel pump as you described. Good idea, though don’t know why that would fail once engine gets hot.

 

[Rivets]

No sealant needed. Hope you got rid of what was on there, because they could cause a leak.

 

[Fescuefreak]

No sealant needed. Hope you got rid of what was on there, because they could cause a leak.

Yes, took flat razor blade and carefully removed the buildup without scratching the surfaces

 

[Fescuefreak]

Today I decided to tackle some stray grass and bug remnants I saw in the gas tank. At first I tried to fish them out but when that didn’t work I disconnected the fuel line to the tank to let it drain…. Guess what? It only dropped out… like 1 drop every 2 seconds… slow! So I removed the rubber bushing and shut off valve ( it was very clogged with dirt and grass) and ordered a new one. My question is, could this be why the mower runs for 20 min or so and then stops? I could always see fuel in the filter which makes me think this wasn’t the problem (maybe the fuel pump could suck enough fuel out despite the clog?). However, if the amount of fuel the pump could deliver was say 99% percent of demand, the fuel in the carb could last a while being replenished almost as fast as needed but not quite. Parts arrive Tuesday but curious what people’s thoughts are.

 

[Rivets]

95% sure you have found your problem. An engine needs far less fuel to run properly, so your full carb at starting was probably clouding your thoughts about how to diagnose the problem. Finally, fuel filter only need to be 25% full for the system to work.

 

[Fescuefreak]

95% sure you have found your problem. An engine needs far less fuel to run properly, so your full carb at starting was probably clouding your thoughts about how to diagnose the problem. Finally, fuel filter only need to be 25% full for the system to work.

I’ll file it under “needed to be done anyway” if it doesn’t fix the issue but hopefully it will. Just not sure how it would run for 20 min after cooling down and supposedly running out of fuel the previous time. How did the carb fill up again to allow another 20 min run time? Maybe idling at startup allowed fuel to fill carb bowl while rpm’s and therefore fuel demand was low?