Engine Dies When Hot

[RWS22554]

Been trying to figure out why my sister's Craftsman mower shuts off when hot. It has a 19hp B&S 33R877-0002-G1 single cylinder engine. My first thought was a bad ignition coil but I replaced that and the spark plug with no change. I also tried running it with the gas cap off, still no change. Right now I have the engine cover removed so I can watch the throttle and governor linkages. What I noticed is that after about five minutes of full throttle the throttle linkage starts fluctuating and if allowed to continue it eventually sputters and dies. If I hold the governor linkage steady it continues to run smooth. Could it be a weak or missing spring or is something else causing it to fluctuate?

This is an OHV engine and I also noticed a small oil leak near the valve cover which drips on the muffler and causes some smoke when it burns off. I don't think it is a bad head gasket but if it was could that be causing the governor and shut-off issues? The engine note doesn't seem to change once it gets hot unless the throttle linkage is allowed to flutter.

 

[bertsmobile1]

Typical of a fuel restriction
Usually floating debris in the fuel tank forming a plug as they are dragged into the outlet so it take some time to happen .
A soft worn out fuel line can collapse and block off the fuel supply as well and this gets worse when hot

 

[sgkent]

what Bert said. Also is the oil fresh and appropriate for the temperature range?

 

[RWS22554]

what Bert said. Also is the oil fresh and appropriate for the temperature range?

I did check the oil and it is clean and full. Not sure what weight oil was used since someone else had already changed it and the filter.

I also pulled the fuel line at the carb and it seemed to flow at a normal rate just from gravity. I will check for debris in the fuel tank but the engine seems to start sputtering everytime at about the same time interval after startup which leads me to believe it is more related to engine temperature which is why I replaced the coil.

Two things I haven't checked yet are whether it has spark once it shuts off and if there is any obstruction (mouse nest, etc.) inside the muffler. I bought a new coil that came in a B&S box but that doesn't mean it's not a cheap Chinese knock-off.

However, just the fact that I can keep it running by holding the throttle linkage steady would seem to eliminate spark or fuel starvation as the issue.

The mower sits in a shed year round and I did have to fix the exhaust system at the end of last summer since the muffler had been knocked loose from the exhaust pipe by someone hitting the back wall of the shed one too many times. LOL. Not sure how long it was like that but there was a big enough gap for mice to get into the muffler...

I also replaced both rear axle seals at the same time because high weeds had wrapped around one axle and tore up the seal causing the plastic transaxle to lose a fair amount of grease.

 

[Tinkerer200]

If you are running that engine for 5 minutes or longer without the cooling shroud, you are in danger of solving your problem permanently.

Walt Conner

 

[bertsmobile1]

We ask you to do tests so we can rule something in or out .
You can think what you like but until you do the tests we will never know.
I work this way
I ask the poster to do some simple tests & usually I tell them why .
When they post the results then I look at them and either make a diagnosis or ask for more detailed testing to zero in on the problem , not the symptoms
If the posted can not be bothered to do as asked then I can not be bothered to give them any more help .

So from here it is up to you

 

[slomo]

I did check the oil and it is clean and full.

Okay I'm stunned for one LOL.

I also noticed a small oil leak near the valve cover which drips on the muffler and causes some smoke when it burns off. I don't think it is a bad head gasket but if it was could that be causing the governor and shut-off issues?

Nope just some smoke. Reseal the valve cover.

Most likely you have grass and grit in the fuel tank passing trash to your carb. Dump the tank and spotlessly clean it out. Carb too is probably in need of a boil cleaning.

Clean your block and cylinder cooling fins while you are at it.

How old is the engine? Might need to pull the head and decarbon the cylinder and valves. All in your engine manual.

 

[Cusser]

I added a spring from the hardware store to the carb of my B&S engine, as the choke spring wasn't strong enough to open the butterfly when I moved the choke lever after a few minutes; so it ran rich and died until I modified it.