Small Engines (Lawn Mowers, etc.): runs when tank half full, spark arrester, briggs and stratton

Question
ben,  i have an older pressure washer with a 3 hp briggs and stratton.  clean air filter, spark plug, and gas.  cranks on first pull.  but only runs for a few minutes.  crank again.  same.  10 restarts later it finally runs on and on.
loosen lid.  same.  then tried refilling only a 1/3 of tank.  runs on and on.  what's up???  thank you.

Answer
Jack

When the engine dies, you'll have to pull the spark plug out, reattach the spark plug wire, ground the case side of the spark plug on the engines cooling fins, pull the starter rope and see if the is spark.

If there is spark, the engine is either:
Running out of fuel.
Getting too much fuel.
Overheating do to a lack or insufficient amount of oil
Has an ignition problem. {See Below}

I suggest you first try a simple test. Keeping the machine level, fire it up without the fuel cap on and see what happens.

If the engines responds normally, the fuel caps vent hole is restricted or plugged. If the machine continues to display the same difficulties, check for any type of fuel restriction between the inside of the tank and the carb.

Another possibility could be a fuel restriction within the carbs fuel flow system. Could be one or more of the fuel ports within the carb may be clogged or restricted. Fuel bowl may have some gum deposits, etc. Basically, your looking for a fuel flow problem.

Yet another possibility could be a muffler or spark arrester restricted with carbon.

When the engine fails to run after determining none of the above is the problem, suspect the ignition system as the cause.