Small Engines (Lawn Mowers, etc.): Engine stalls and no power, briggs no power

Question
I have a Craftsman mower with a Briggs engine model# 31H777-0297E1. It had started hunting or surging after it warms up. It runs good when cold. Yesterday, I tried to adjust the carb because it was running lean and now it will stall but will immediately restart. I think I have it too rich but am not sure. Also, it has been very low on power since last year. It will bog down in 4-5" grass and I must use 1st gear and somtimes I have to stop and let the blades build up speed. I had the valve cover off last week and the valves seemed very loose but I didn't make any adjustments. Can this cause the low power problem? I didn't check the valve clearance but I guess they had .020" or more. I read on this site that they should be between .004"-.009". I know they have a lot more than that but want to ask for advise before I really screw something up. What do you think? Thanks in advance.

Answer
http://faqs.custhelp.com/cgi-bin/faqs.cfg/php/enduser/std_adp.php?p_faqid=3441&p...

That site will help you with valve adjustment.

The other problems are probably carburetor related.  The idle mixture screw should be set at 1 1/2 turns out and then with the engine at slow idle, turn it in until the engine runs rough and then back out until it cleans up and starts to run rough again.  The halfway point between running rough is the setting.  You have to turn it very, very slowly.

Probably you have an internal problem with the carburetor.  I'm assuming you have the Nikki carburetor as the Walbro has a limiter on the idle jet.  I don't bother rebuilding the Nikki as the kit is half as much as a new carburetor.  I also seldom bother rebuilding the Walbro carb as it too has an expensive kit and doesn't always come clean.  So to me, it's more cost-effective to replace the thing.  

Now I do pull the bowls off and check for dirt and the float level before replacing.  I suspect you'll find that the float, when the carb is turned upside down, is angled upwards on yours, causing the engine to lean out.

Always start with the basics, new plug, filters, check the fuel lines, I replace fuel lines whenever rebuilding or replacing carburetors.  Then clean the carb and evaluate the problem.  Let me know if you have any questions.  Thanks, PK.