Small Engines (Lawn Mowers, etc.)/briggs&stratton engine


QUESTION: This is a b&s 12.5hp I/C 2003 engine it will not start we have stripped it down could not find anything wrong with it rebuilt it still the same it blows the fuel back through the carb we have squirted fuel through the carb and it does try to run can not see why it blows it out instead of sucking it in

ANSWER: When you say you "rebuilt" it what parts did you replace?  Did you remove the cam shaft, valves and crankshaft?


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QUESTION: This engine was blowing fuel back through carb that is why we stripped it down we built it back up grinding valve in and replacing gaskets and oil seal we set valve clearance when we came to start it again it was the same blowing fuel out of carb . We removed valves camshaft and piston but not the crank. The engine would not fire before or after the work on the engine .The engine is in a Stiga ride on mowewr and had been stood in a building for 3 months over winter I started it up and drove it into workshop to work on cutting deck I did the bed come to start engine and it would not start on inspection it was blowing fuel out of carb that is why we stripped it down. I have MS and use the tractor to get about as I cant walk without crutches and this enables me to get about and do small jobs in my workshop thank you Garry

ANSWER: Were there any dots or lines on the camshaft and crankshaft for setting the cam/crank timing?

What are the valves set at?

Is the flywheel key sheared?


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QUESTION: There are dots setting timing they are spot on valves were set as spec sheet and there is a key way in place

Fuel coming back through the carb can only be caused by mechanical timing, the intake valve is open when the piston is coming up the cylinder or possibly ignition timing, sheared flywheel key.

If the mechanical timing is correct (timing dots and valve clearance) and the flywheel key is not sheared (ignition timing) then no gas should come back through the intake valve.

Did you lap the valves before installing the head?  Is the intake seat bad?


Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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