Needing some help from a small engine guru.

[midwest]

I'm not real mechanically inclined.....(Just needed to get that out there).
I have a Ferris 61 inch ZTR mower with a 30 horse Briggs engine. Last week I was pulling my sprayer and was only running about half throttle. Right before I parked it the motor started to bog down like it was running on 1 cylinder. I revved it up and it smoothed out and I didn't think anything of it. Today I started mowing and about an hour in it did the same thing, bogged down. I pulled the spark plugs and one looked bad so I replaced both and it started right up so i thought that was it. Once it ran for 20 minutes same thing. I shut it off and checked the temps on both sides of the engine exhaust. The left side was only 150 degrees and right side was around 500 so I figured which one wasn't firing. I checked compression in both sides and they were both over 130 lbs. After it cooled off it started it runs smooth. This time I let it run until it bogged again. I checked the temps on both heads and the left head was over 900 degrees and the right head is just under 600. So I assumed the left side is overheating and causing a valve to stick???? I also "hoped" that I would remove the shroud and find a mouse nest of a bunch of grass in there blocking the air flow. The fins on the head were pretty clean. That's about the extent of my mechanical knowledge... Any ideas on what to check next? I have no idea what could be happening inside the engine that would cause one side to overheat. I am not sure if the over heating is causing something else which shuts that cylinder down or if something is wrong inside that is causing it to overheat.

The mower is a 2014 and only has about 300 hours on it. Air filter is clean and I run Rotella T14 oil and briggs OEM filter. Its a Briggs Commercial Turf engine.

This morning I called the dealer I got the mower from. Their service department is 4 weeks out....The service guy said he guesses it is the coil. I could see the engine getting hot causing the coil to fail but could a failing coil cause that head to get hot?

 

[DanMcG]

First question is, do you trust the reading of your thermometer?

 

[midwest]

It is my neighbors and he is an auto mechanic by trade. When we checked the temps on the "good head" it was around 500 and when we checked the temps on the "good exhaust" it was around 600. When we went to the bad head it shot up, I cannot say it is perfect but I have no reason to think it is off by several hundred degrees when pointing it at the left side head. I didn't see what brand it was but he has all quality tools...

 

[dvdswan]

If one side is firing and the other is not, its adding stress on the side that is firing. So it makes sense on the coil breaking down. Just a thought.

 

[89Suburban]

If one side is firing and the other is not, its adding stress on the side that is firing. So it makes sense on the coil breaking down. Just a thought.

Yes loosing spark when heating up is a good indicator to me for this. Electrical circuit expands with the heat and gap/break in the circuit occurs. When cools down works fine gap/break is connected and operating.

600* is normal operating high speed temp of this type of engine on the exhaust side. 400* at low speed. Intake side should not exceed 250*.

 

[midwest]

OK thanks. I think (fingers crossed) it is just the coil(s). I have ordered two OEM Briggs coils for it. There was a mistake reading the thermometer. My neighbor thought it was reading at 1000 degrees and come to find out it was only 100 and some. I couldn't find the specs. for his thermo gun online but I called Mac tools and gave them the model number and his doesn't even go that high. That makes me feel it is definitely just a coil issue. I ran it for about 10 minutes tonight until it started cutting out again and checked the temps on the head and they were just over 100 degrees, not close to 1000 like he said when he was yelling to "shut it off" lol. I kept trying to figure out what would cause an air cooled engine to get that hot and in the back of my mind I was thinking I was going to have to buy a head(s) and lord knows what else. Coils should be here on Friday, I'll know for sure then.

 

[AuroraGirl]

I'm not real mechanically inclined.....(Just needed to get that out there).
I have a Ferris 61 inch ZTR mower with a 30 horse Briggs engine. Last week I was pulling my sprayer and was only running about half throttle. Right before I parked it the motor started to bog down like it was running on 1 cylinder. I revved it up and it smoothed out and I didn't think anything of it. Today I started mowing and about an hour in it did the same thing, bogged down. I pulled the spark plugs and one looked bad so I replaced both and it started right up so i thought that was it. Once it ran for 20 minutes same thing. I shut it off and checked the temps on both sides of the engine exhaust. The left side was only 150 degrees and right side was around 500 so I figured which one wasn't firing. I checked compression in both sides and they were both over 130 lbs. After it cooled off it started it runs smooth. This time I let it run until it bogged again. I checked the temps on both heads and the left head was over 900 degrees and the right head is just under 600. So I assumed the left side is overheating and causing a valve to stick???? I also "hoped" that I would remove the shroud

whats your air gag?

and find a mouse nest of a bunch of grass in there blocking the air flow. The fins on the head were pretty clean. That's about the extent of my mechanical knowledge... Any ideas on what to check next? I have no idea what could be happening inside the engine that would cause one side to overheat. I am not sure if the over heating is causing something else which shuts that cylinder down or if something is wrong inside that is causing it to overheat.

The mower is a 2014 and only has about 300 hours on it. Air filter is clean and I run Rotella T14 oil and briggs OEM filter. Its a Briggs Commercial Turf engine.

This morning I called the dealer I got the mower from. Their service department is 4 weeks out....The service guy said he guesses it is the coil. I could see the engine getting hot causing the coil to fail but could a failing coil cause that head to get hot?

A 2 cylinder is surprisingly able to perform okay on one cylinder or with a power balance way off, without being that obvious, if its big enough engine. Have you used a vacuum gauge at all?

 

[midwest]

2 new coils and it's running like a champ... Thanks all