I have a 3.5hp Briggs &Stratton that gives a hard start and will only idle for a minute before stalling. I had it work for a while but stalled once I tried to cut the grass. I removed the carburetor cleaned it with carb spray , but same results. Removed the plug put in a new one and after three more attempts, it was fouled up(black). Cleaned it up, removed the air filter re-started but still only ran for a minute at an idle speed before stalling. Any ideas to solve this problem. Could it be the head gasket needs changing?

Fresh fuel? Tank to carb diaphragm? Plug wire?
Oil level too high or low?
Maybe this can help:
Small Engine Problems Troubleshooting and Repair | Briggs & Stratton (http://www.briggsandstratton.com/us/en/support/faqs/engine-problem-solving-tips)

Fresh fuel? Tank to carb diaphragm? Plug wire?
Oil level too high or low?
Maybe this can help:
Small Engine Problems Troubleshooting and Repair | Briggs & Stratton (http://www.briggsandstratton.com/us/en/support/faqs/engine-problem-solving-tips)

Thanks for the information. Oil leve is fine and plug wire seems OK as it does start and will run until it encounters stress of cutting grass- on some occasions. I suspect it is a carb prob, so I will try replacing the carb to tank diaphragm... if I can get it. She's about 15 years old pull start.

If it stalls when cutting starts, how about the governor?
If you google youtube mower governor problems (or similar) you should get some good videos on small engine governors.

If it stalls when cutting starts, how about the governor?
If you google youtube mower governor problems (or similar) you should get some good videos on small engine governors.
I honestly think it's a carb prob as it will just stall after about a minute of running. It's almost as though it simply runson the prime fuel and stalls once it is used up. I tried priming again as it spluttered, but it never catches back up.

The only suggestion I can make is to try that B & S troubleshooting link I provided. I put "engine starts but won't keep running" in the site search box and 25 different pages came up for review.
Good luck.

The only suggestion I can make is to try that B & S troubleshooting link I provided. I put "engine starts but won't keep running" in the site search box and 25 different pages came up for review.
Good luck.
I will go check the B&S site as I just changed the carb diaphragm and accompanying gasket with no change in the problem.