Small Engines (Lawn Mowers, etc.): craftsman push mower, briggs stratton engine, reddish orange color

Question
I have a craftsman push mower #917.388391. 6HP briggs/stratton engine #12h802-2675-b1. Mower ran fine for the past 4 years. Then late last October it would start up and run just fine for 30 minutes, then it would act like a bad spark plug, sputter and lose power but not die. So at the beginning of this mowing season I changed the plug, new air filter, and fuel additive. No improvement. Figured it must be the carb. I took off the carb and took it with me to the local shop to get a kit. Although I told them where it had come from, they told me it was a tecumseh carb, and I got a new kit and float.  Soaked the carb overnight, blew it out, cleaned it up and installed all the new parts, except the welsh plug. It ran like new for 15 minutes then gradually went downhill, died and would not restart. Acted like a classic coil situation, so I changed the coil. This time, it ran great for 5 minutes then did the same old gradual downhill thing, starts sputtering, backfiring, little to no power and eventually dies and is very difficult to restart, if it does restart, it runs terrible.
Taking a look a few days ago, I was removing the carb to check it once more, when I pulled the fuel line, reddish-orange colored gas spilled out of the line for a second, then clear gas came out.  Checking the carb bowl, reddish-orange gas was is it. Thinking maybe something was in the tank I took it off and cleaned it out. Put everything back together and it still ran horribly. Pulled the gas line once more and the gas in the carb is again reddish-orange. I'm completely stumped now. Thinking engine rebuild kit now. Thanks for any thoughts.


Answer
Hello O:

Remove the Gas Tank and Close Off Any Holes. Pour some BBs into the Tank and Shake Vigorously. Then Dump the BBs Out of the Tank and Clean with Compressed Air and a Damp Rag. This will Knock the Varnish inside the Tank Loose and Allow you to Better Clean the Tank. The Reddish Orange Color to the Gas should now be Gone. Disassemble the Carburetor and Blow it Out. According to the Breakdown of this Mower, the Engine is a Briggs, Not a Tecumseh; so the Shop was Wrong. The Carburetor Kit, Briggs and Stratton Part Number is 498260. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Thanks.

Respectfully

John