Runs rough when hot

[plpitts1]

I have a Yardmachine 21" with a B&S 550ex, engine model #09P702-0145-F1, Serial #1608165118199. Starts first pull, runs great untill it gets hot (about 4 or 5 minutes) and starts acting up. Sounds like it starts running a little rich or is missing. Has new plug, air filter and fresh gas. Tried removing gas cap to check for cap vent. Checked valves, set at .006. The intake valve was tight. I believe they are supposed to be between .004 and .008. Could use a little help.
Thanks,
Pat Pitts

[38racing]

if it has a fuel shutoff then shut it while still running and see if running improves. if yes then reopen and see if it goes bad again.that would indicate that it's flooding.

[KE4AVB]

From what I have seen of the 09P there is no shut off valve but you should be able clamp the fuel line to test as 38racing suggests. The ones I have been running into have trash in carbs so I add an inline fuel strainer ie Briggs pancake filter.

If not the problem remove the engine shroud and check first that there is no mouse bed under it. Then try replacing the ignition coil as it sound a failing ignition coil's electronics. The new coils are now using surface mount semiconductors and can be more sensitive to overheating related problems.

[bgsengine]

check the flywheel key too. - First thing I do on any walk behind mower with symptoms like yours - allows to also check for mouse nest and any visiblecoil issues as KE4 noted

[plpitts1]

Thanks for the reply's. Pinched off the gas, no change, checked flywheel key, looks good (no birds nest or dirt daubers). Will update in 7 to 10 days.
Appreciate it,
Pat Pitts

[bgsengine]

Try another new plug. Especially if it has a Champion or Autolite in it. Not uncommon to have them bad right out of the box. Also make sure you got the plug gapped correctly.

[hanz63]

Something goofy with these too is having a fuel tank that is filled to the top- will spit fuel out of the tank vent into the air filter.

[plpitts1]

Thanks, tank half full of fuel. Yes, it is a new Champion plug, will try another, thanks for the reply's
Pat

[Skywatcher]

Hi P.L. Pitts

Once the engine has warmed up and started running rough, clamp the fuel line off and let the engine run until is dies, then answer these yes-or-no questions.

1, Did the engine continue to run rough right up to the point where it died?

2, Did the engine smoothen out just a few seconds before it died?

3, Did the engine smoothen out at about the half way mark between clamping the fuel line and the engine dying?

4, At any point, did the engine start surging at any time before it died?

Answer these and we'll see if we can give you any more ideas. All the best,

Sky

[RJRacing]

check the choke thermostat, make sure it's pulling the choke all the way open when the engine is warm