# 12.5 hp Briggs & Stratton will not fire



## dt21 (May 13, 2011)

I have a Briggs 12.5 hp motor that was give to me with a siezed up exhaust valve. I took the motor partially apart to replace the valve and valve spring. I reassembled the motor with the cam and crank sprockets aligned per their marks. I have fuel, spark, air/exhaust, but the motor refuses to fire up. I have sprayed ether to see if it would fire off that, and have even sprayed ether in the combustion chamber and tried it that way. Still no fire. With the plug wire removed and engine cranking, I have a good spark. I have fuel inside the carb bowl and can feel the exhaust pumping out of the muffler. Does anyone have an idea what would keep this engine from firing?


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## 2and4StrokeTech (Apr 6, 2011)

How's the compression? Is the intake valve moving/seating?


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## dt21 (May 13, 2011)

I ran a compression test and have almost no compression. It also leaked down almost immediately. I'm assuming I'm going to have to replace the rings and lap/grind the valves too. Any ideas/suggestions?


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## jrrdw (Jun 26, 2010)

What are the engine numbers? Model, type and code.

It's hard to get a compression reading from Briggs & Stratton because of the compression release. Check you valve clearence before you do anything else. Should be between .004 and .006 for both valves.


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## dt21 (May 13, 2011)

The engine is a 286707 type 0441.01 It's a vertical shaft engine with standard valve set up.


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## jrrdw (Jun 26, 2010)

Set the spark plug gap at .060, that will simulate the spark plug being under compression and fuel conditions. Just because the spark plug fires laying on the head bolt or muffler doesn't mean it's sparking inside the combustion chamber. 

Checking the valve clearance has to be done when installing a new valve. Check the clearance in between the valve tappet/lifter and the valve stem that sticks out of the spring. There must be clearance there when the valve is all the way closed and the piston is at top dead center on the compression stroke.

Does this engine have a cast iron sleeve in the cylinder?

With the numbers you just gave ignore the clearances I gave in the prior post, I thought this was a smaller engine.


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## dt21 (May 13, 2011)

I will check that valve clearance and see if that is the problem. It may take a couple weeks when I get the time though. I appreciate your help. Thanks!


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## jamez46 (Nov 6, 2013)

Have you checked that the fly wheel key way matches the key way on the shaft, the spark from the mag has to arrive at a specfic time. If off, it will never ignite when its suppose to.


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## Basementgeek (Feb 7, 2005)

Hi and welcome to TSF jamez46

I assume they have it figured out by now as this is a two+year old thread.

BG


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## jamez46 (Nov 6, 2013)

I had an atv that quit running on me, and even though I had spark at the plug end, I needed to find out is there was spark at the other end of the plug, which turned out that there was not. I simply used an allegator clip to connect the cathode of the plug to gnd, cranked it over and no spark. Changed the plug and all is well.


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