At Wits End

[bulfin]

Don't know what else to do, so I am trying a hail Mary here. Maybe one of you can give me some help.

My lawn mower (Craftsman rear engine rider, 13.5 hp Briggs and Stratton engine) cranks and runs well for about 5-10 minutes, then dies and will not crank until much later. Here is what I have done so far, not necessarily in this order.
New air filter
New gas
Oil not overfilled
Drained gas tank
Spark plug looks okay
Made sure gas flows easily to carb
Cleaned carb
New carb/filter/fuel lines
Cleaned armature (coil)
New armature
Removed exhaust/muffler (ran fine then died, would not crank)
Has spark when I try to crank it after it dies
Checked compression - 90 lbs, about right for engine
I decided to take it to a repair shop. One asked what I had done to it, when I told him he said I had done everything and would not take it. Another said bring it in and we will look at in six weeks. Meanwhile my neighbours are getting restless about my high grass !

So anyone got any thoughts?

Thanks,

Bob

[rgh0]

Plugged vent on gas rank cap ?

cheers
Rohan

[berni29]

Hi

Perhaps a heat soak related issue? Not that it helps much! I have a mower that will just not start. I just went and bought a bigger better one on facebook marketplace. Having said that I still want to get the original one going.

Best of luck

Berni

[vxah]

Little confused Bob, you say when it dies it won’t crank again for some time? Did you mean to say it cranks but won’t fire and run? Would seem to make more sense?
I take it this is a four stroke engine? What about the valve clearance, have you checked it? I know generally they are tighter when cold but depending upon engine construction it could be the other way around causing an issue when fully warmed up?

[h20hamelan]

Sounds like a fuel issue, weak spark maybe.
Most everything is made in China now, components internally too.

Regularly, the new crap is faulty so soon. You can no longer be assured of anything being quality.

My wood splitter has had 3 new coils in the last two years, doubt this one will last. So I have opted for external coil and battery.

[bulfin]

Thanks for the replies. Some answers to your question:

Gas cap vent was checked and also ran it until it died with the gas cap off

It turns over and sparks after it dies, but does not run

I have not checked valve clearances

It is logical that it is heat related

Could be the new armature is bad - I will try another one and see if it helps.

Again, thanks for the replies.

Bob

[Quart Meg Miles]

Bob, buy a scythe and do it manually, it will take less time than sorting the engine and soothe all the stress away too.

Perhaps it's running far toio rich, so it starts fine when cold but chokes when warm and won't restart. I had a chum with a racing car much like that, called "Escargo" (French for snail), it went faster when he turned the petrol feed off!

[Tim]

Have you tried swapping the coil?

[bulfin]

Yesterday I tried another new coil - same results.
Given my respect for Rohan's advice, today I tried a different fuel cap - same results.
Meg, at 75 with a bad back, I don't think I could handle push mower, much less a scythe . On these simple carbs, the only adjustment seems to be idle, but I will look into your fuel idea.

Simple problem AIR/FUEL/SPARK. Guess I might have to get another mower.

Bob

[h20hamelan]

how well did you clean the carb

[vxah]

Air/fuel/compression/spark

[2cams70]

Very common with small engines for it to be valve clearances. They are very prone to closing up over time. With very little or no clearance a valve can stay open when hot due to valve stem expansion when hot

[TomR]

Here's a long shot. I had a Honda engined mower that would stall and not restart until it cooled down. Turned out the exhaust valve was sticking open when hot. Marvel mystery oil in the gas solved the problem.

[bulfin]

Thanks for the replies.
Carb is new
I did not test compression after it quit. I'll try that if I can do it without bad burns; spark plug is surrounded by exhaust pipe..
I will look at Youtube to see what it takes to pull the valve cover and check valves.
I wish I had taken the seat off and jumpered the seat cutoff circuit before now.

[bulfin]

Thanks to all who mentioned compression and valves; you were correct. I pulled the valve cover and found the exhaust rocker arm loose. Also, no cap on the valve stem. I pulled the head, cleaned everything up ordered a valve cap and gaskets and put it back together. Ran well for a few minutes and died. I thought it was a classic case of solving a symptom . What caused the rocker arm to be loose - decided it must be a bad rocker arm retainer so I got a new one and put it all back together. Today I tried it and got the same results, ran fine until it got hot and then stopped. Pulled the valve cover and the exhaust rocker arm is loose again! Valves and pushrods appear to be ok, everything looks good when I watch the valves as I turn it by hand. I am ready to shoot it.

Bob