Fuel Delivery Issue When Hot...I think

J

JRonascag

Member
I have a ~15 yr old Scag Turf Tiger with the Kohler 27hp carbureted motor, w/ 1000 hrs on it.
It has been running great until now. I just completed my Spring maintenance (oil, filter, fuel filter, etc.).

Now, it will start and run just fine for about 10-20 minutes (which I assume is getting good and hot at that point).
Then, it bobbles a couple of times and dies. I can immediately choke it and it restarts just fine, but won't stay running.
If I let it cool down, starts and runs just fine until it gets hot again.

So, I made sure it has the right fuel filter and in fact I had accidentally put one on for a EFI motor, which I thought might be too restrictive. Replaced it with correct one and...still the problem.

I happened to have a new fuel pump for it (mechanical), so I put that on. Still the problem.

I would suspicion the coil, but the fact that it will start back with choke (even though it doesn't run well) leads me away from an electrical issue.

As FYI, I had a vapor lock problem a few years ago, where one of the fuel lines had lost its heat shield and was boiling the fuel, but the new heat shield appears fine.

It just seems suspicious that the problem started right after my Spring maintenance, but I can't think of anything I did that would cause this.

So...I'm at a loss and would appreciate any thoughts.

Thanks in advance!
 
JRonascag said:
I have a ~15 yr old Scag Turf Tiger with the Kohler 27hp carbureted motor, w/ 1000 hrs on it.
It has been running great until now. I just completed my Spring maintenance (oil, filter, fuel filter, etc.).

Now, it will start and run just fine for about 10-20 minutes (which I assume is getting good and hot at that point).
Then, it bobbles a couple of times and dies. I can immediately choke it and it restarts just fine, but won't stay running.
If I let it cool down, starts and runs just fine until it gets hot again.

So, I made sure it has the right fuel filter and in fact I had accidentally put one on for a EFI motor, which I thought might be too restrictive. Replaced it with correct one and...still the problem.

I happened to have a new fuel pump for it (mechanical), so I put that on. Still the problem.

I would suspicion the coil, but the fact that it will start back with choke (even though it doesn't run well) leads me away from an electrical issue.

As FYI, I had a vapor lock problem a few years ago, where one of the fuel lines had lost its heat shield and was boiling the fuel, but the new heat shield appears fine.

It just seems suspicious that the problem started right after my Spring maintenance, but I can't think of anything I did that would cause this.

So...I'm at a loss and would appreciate any thoughts.

Thanks in advance!
Click to expand...
Make sure your fuel tank is free of debris. Drain and blow out fuel line and tank as needed. Make sure you are getting good steady fuel flow from fuel pump to carburetor.

At 1000 hours the ignition coils and 20 minute run time until engine has performance issues is suspect. However, if you can choke it and it recovers, that points to fuel. Do you have to keep choking it off and on to maintain engine running? Does it run strong once it recovers, or down on power, miss, backfiring, etc.?
 
If your EFI filter was the 24 050 13-S filter that is the old standard fuel pump filter for Kohler. So that is not the issue. If it was it would still be an issue since the Kohler EFI engine still uses a vacuum style pump to charge the EFI pressure pump. And the Kohler Command will attempt to run under full choke even with a failed afterfire solenoid on the carb. So I would run the engine until it dies and then cycle the key to determine if the fuel solenoid is still working when hot.
 
Tiger Small Engine said:
Make sure your fuel tank is free of debris. Drain and blow out fuel line and tank as needed. Make sure you are getting good steady fuel flow from fuel pump to carburetor.

At 1000 hours the ignition coils and 20 minute run time until engine has performance issues is suspect. However, if you can choke it and it recovers, that points to fuel. Do you have to keep choking it off and on to maintain engine running? Does it run strong once it recovers, or down on power, miss, backfiring, etc.?
Click to expand...
Once it dies (after 20 minutes or so), I can immediately choke it and re-crank it, but it runs terribly and I have to keep coaxing it along with on/off choke. Once I let it cool down for ~ an hour, it runs perfectly fine with full power for about 20 minutes and dies again.
Much thanks!
 
ILENGINE said:
If your EFI filter was the 24 050 13-S filter that is the old standard fuel pump filter for Kohler. So that is not the issue. If it was it would still be an issue since the Kohler EFI engine still uses a vacuum style pump to charge the EFI pressure pump. And the Kohler Command will attempt to run under full choke even with a failed afterfire solenoid on the carb. So I would run the engine until it dies and then cycle the key to determine if the fuel solenoid is still working when hot.
Click to expand...
Much thanks. Forgive my ignorance, but When I cycle the key, how do I know if the fuel solenoid is working?
 
JRonascag said:
I just completed my Spring maintenance (oil, filter, fuel filter, etc.).
Click to expand...
Ever clean the cooling fins?
Ever do a valve adjustment?
Ever de-carbon the cylinder/s?
JRonascag said:
I can immediately choke it and it restarts just fine, but won't stay running.
Click to expand...
Tells me lack of fuel delivery.
JRonascag said:
I happened to have a new fuel pump for it (mechanical), so I put that on. Still the problem.
Click to expand...
Ever pull the fuel hose off AT the carb inlet? See if she has water or a poor fuel flow?
 
slomo said:
Ever clean the cooling fins?
Ever do a valve adjustment?
Ever de-carbon the cylinder/s?

Tells me lack of fuel delivery.

Ever pull the fuel hose off AT the carb inlet? See if she has water or a poor fuel flow?
Click to expand...
Well, I just pulled the fuel line off, right at the entrance to the petcock (fuel shutoff). Embarrassingly, the petcock is almost completely stopped up. I’m guessing this is the issue but will let you know once I replace it and run it awhile.
To answer your questions: I have never pulled the engine shrouds and cleaned the cylinder fins. Never realized I need to, but will definitely do that now.
I’ve also never adjusted the valves, so probably well overdue and will look into it.
Thanks!
 
JRonascag said:
Well, I just pulled the fuel line off, right at the entrance to the petcock (fuel shutoff). Embarrassingly, the petcock is almost completely stopped up. I’m guessing this is the issue but will let you know once I replace it and run it awhile.
To answer your questions: I have never pulled the engine shrouds and cleaned the cylinder fins. Never realized I need to, but will definitely do that now.
I’ve also never adjusted the valves, so probably well overdue and will look into it.
Thanks!
Click to expand...
OK, I can work with you. We all start some place. Like the fact you owned up to it. (y) Speaks highly of you sir.

Cooling fins are a yearly or more often maintenance item in EVERY small engine manual. Most are air cooled. If you neglect this, engine damage can come your way. All around the or each cylinder fins need to be spotless. As in a NEW engine looking clean. Clean as in hospital clean.

Valves are a yearly for a goooood running engine. Only takes about 3 minutes to check and reinstall the cover. NO RTV on the valve cover either. Use a non hardening sealant for the next guy not to pull his hair out trying to CLEAN and REMOVE the valve cover. I dislike RTV with a passion.


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Also you need to de-carbon each cylinder every like 7-10 years. See your engine manual for proper intel. Behind each valve and combustion chamber. Anyplace carbon will accumulate.
 
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