Small Engines (Lawn Mowers, etc.): Engine flooding, sears craftsman lawn tractor, craftsman lawn tractor

Question
Dear Michael -

I originally asked this question of Robert Kapsy, who provided me a preliminary answer.  I need to follow up, but Mr. Kapsy is now shown as "maxed out."  I'm hoping that perhaps you can complete the answer.  Here's what I wrote originally:

Dear Mr. Kapsy -

I am having a flooding problem with my Sears Craftsman lawn tractor. It's model #917.270821, with a Briggs & Stratton 19.5 HP Turbo-Cool engine. I don't see a model number on the engine. I bought the tractor new in 1998.

This is the first time trying to start the tractor this year. When I crank the engine, I get the aroma of raw gasoline, but the engine doesn't fire. When I removed the air cleaner and cranked it, raw gasoline was spit out of the top of the carburetor in small drops. Choking didn't seem to have any effect. As this went on for several attempts, enough raw gas came out the top of the carb that a small pool of gas formed in the air cleaner tray.

I finally got the bright idea that it was getting too much gas somehow, so I put a pair of Vise-Grips on the fuel line. Cranking for several seconds finally got the engine to start and run for about 30 seconds. Applying and removing the pliers finally allowed me to warm up the engine, and it actually ran for a while with the pliers clamped on the fuel hose. I started mowing and got maybe 100 yards before it quit again.

I stored the tractor outside under a tarp over the off-season. All gas used last season was treated with Sta-bil. I didn't run all the gas out of the tank at the end of last season. I had the engine tuned up at the beginning of last season.

I suspect that there is gunk in the float bowl, which is causing the flooding condition. Being a klutz on and off, I'm hesitant to remove the carb and disassemble it without some expert idea of whether this is the correct approach. I will greatly appreciate any light that you can shine on the problem. Please let me know if you need any further information. Thanks.

Colin Brown
colin@nexet.net
Answer   Colin, Go to the Briggs web site and there should be info on where to find the model and type number,,,,,is it a 2-cylinder engine? I suspect it is. Anyway, yes it seems that you have a flooding condition where the carb may have to be removed and cleaned.The carb is easy to take apart but you may have to install a new needle add seat....Let me know what happens ..Bob
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That's the end of Bob's answer.  What follows is what I did this evening.  
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I removed the carburetor this evening and cleaned everything I could find, making sure all passages were clear and the float moving freely.  I reinstalled the carb and got exactly the same result - gas spewing from the air intake.  

Bob had asked me to find the model number of the engine, which I did.  It's a B&S, model number 42E707, type 2631E1, code 9809225A.  It almost acts as if something is forcing too much gas into the carburetor, but I don't know enough about how these things work to know anything for sure at this point.  I would greatly appreciate any light that you can shine on the problem.  Thanks very much.

Colin Brown
colin@nexet.net

Answer
Hi Colin,

When I hear about fuel coming back out of the carb I think of an intake valve not seating.  This would cause the compression to come back into the carb.  You could do a compression test to confirm or depending on how much leaking is occuring, you would feel the pulsating at the carb throat if you cover it with your hand while cranking.  Other than that, the problem would be, as you have suspected, the carb delivering too much fuel.  I would recheck the float needle and seat, float height adjustment or for a fuel logged float.  When severe, any of these would cause leaking when the engine is off.  
Did adjusting the mixture screws change anything?

Let me know what you find.
Michael