A little off topic here I know, but I figured someone in here can help. I have a lawn tractor with a 12.5 HP Briggs & Stratton engine that won't run for more than 2 minutes, to restart I have to wait until the engine cools down. It almost sounds like its grounding out or starving for fuel. (I've eliminated the fuel I think)Here's what I have done....drained and changed the fuel, cleaned the breather hole on the gas cap, new plug and fuel filter, checked for spark on the new plug and that’s good, used a carburetor from another engine (matching, got the same 2 min. run time), checked what wires I could see for worn away insulation, checked the three safety switches that are on the seat, clutch and cutting blades. All three still have a good "clicking sound" and return spring is working. The battery has a fairly good reading under load, so I'm stumped! Oh ya and for good measure changed the oil and oil filter!

 

Have you tried running it without the fuel cap in place?

Have you checked the spark after it warms up and quits?

Could it be a sticking valve? I have an old Techumseh on my Toro that will do that on a hot day. It will stick after about 30 minutes and loses compression until it cools off for a few minutes.

 

Sounds electrical to me. Like a coil going bad on a gasser. They get hot and expand and then don't work until they cool off. Don't know whether yours has anything exterior like a solenoid that could be doing that or not, but I would guess that or maybe the magneto?

 

Look and see if there is a hose and filter in the gas tank, if the hose is old and soft it will start but then the hose will colapse and starve the engine of gas, lots of push lawn mowers do that, and the tank filter may be getting clogged also.

 

I have run it without the fuel cap, I feel like an imbecile but I never checked for spark after it shuts down so I'll have to try that. Not sure on the sticking valve, is there a way of checking that? Thanks for your help, see I knew someone would try and help!!!!

 

I had a Lawn Boy mower that did the exact same thing. It would crank right up but when the engine warmed up it would die and not crank up again until it cooled down.

I did some research on the internet and determined that it needed a new exhaust valve.

From the website that I used to determine this...

A local mower shop was going to charge me the price of a new mower to repair it so I opted to buy a new Toro instead.

Good luck.

Here's a site you might check out...

http://www.repairfaq.org/sam/lmfaq.htm

 

Thanks everyone for your help, I'll head over to that site Hoss and check it out. This may be a way for me to talk my wife into getting a "zero turn" mower. Maybe I'll just let the locals use the yard for grazing!

 

coil problem. The coil's overheat on the older Briggs vertical shaft engines.

 

You can check for the bent valve by either listening or with the pull starter- if it turns over freely (no compression) it might be a valve.
Did you clean the engine? Some of these engines have an overheating protection and if you've got dirt on it it will get hot and the protection does it's job.

Just my 2c
AlpineRAM

 

Try the coil first. I teach Small Gas Engine Repair and I am trained on Briggs & Stratton.

 

I don't think this is your problem since you changed the oil, but mine used to do the same thing until I realized it had no oil. Adding oil cured the problem.

 

If it's fairly new it will have low oil shutdown. The fact that it is starting then dying would lead me to believe that the oil is up to snuff. but it could be a bad sensor.

run it and as stated above...

check for spark after it dies

check for fuel flow after it dies

check the compression after it dies

 

I'm going to vote coil on this one...

How old is the mower? I'm assuming is has some type of solid state electronic ignition??

 

if it is an ohv may need valve adj. should have a vacume fuel pump, if bad would cause the problem. can you post model and type.
Clark

 

I'll vote for ignition module, but the sticky valve is also a possibility. If you have access to a compression tester you should be able to test the spark and compression after it dies. You should probably use a spark tester when testing the spark as it may still jump the spark plug gap but be weak (I hope that made sense).