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JohnF2015, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1100
Experience:  Owner/Service Technician at S & J Small Engines
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Exmark 26 EFI Kohler. Engine periodically throttles back as

Customer Question

Exmark 26 EFI Kohler. Engine periodically throttles back as if it is having fuel delivery problems but goes right back to full throttle a few moments to minutes later. Now has the same issue but will not clear itself to run full throttle. Pumping black soot from pipe.
JA: Can you guesstimate how old the engine is? And has it done anything like this in the past?
Customer: I would guess 2001 ish. It has had the problem intermittently over the last year or so. Dealer was unable to trace the problem.
JA: Do you plan on doing the work yourself?
Customer: yes, I've spent plenty of money at the dealer with no results
JA: Anything else we should know to help you best?
Customer: Such as?
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Small Engine Technician about your situation and then connect you two.
Submitted: 11 months ago.
Category: Small Engine
Expert:  JohnF2015 replied 11 months ago.

Hi, my name is***** will be assisting you.

The first thing that comes to mind is if you have an air pocket in the fuel system on the efi it will cause this type or erratic performance. I would suggest that you bleed the fuel line and make certain that there is no air in it. You can do this by using the valve that is in the fuel rail, it is similar to a valve stem and if you push in on it with the key on and the fuel pump operating it should disperse any air out of the lines. If that doesn't solve your performance issue then I would be looking at one of the ignition coils as a potential problem, if may not be firing all the time which will cause the symptoms that you are having.

Thank you it has been a pleasure to assist you.

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Customer: replied 11 months ago.
Would a leaking head gasket cause the issue? Just found that one cylinder is leaking. I can see the exhaust coming from behind the pipe on the cylinder head base.
Expert:  JohnF2015 replied 11 months ago.

A leaking head gasket could cause you to loose power on the one cylinder. It would not gain power back however as you had initially commented. It would affect the O2 sensor and could make the engine run real erratic.

It is possible that the leaking head gasket could be causing the problem.