# briggs and stratton carburetor backfire



## snowdog88 (Apr 28, 2005)

I replaced the connecting rod in a B&S 6.5 HP Intek. There appears to be no damage to any other component of the engine. Now, it will only back fire through the carb when trying to start. The first obvious answer is that the timing is off. I have checked the following:

* The dot on the crank gear lines up with the grove in the cam gear

* When they are lined up, the piston is just before TDC

* The mag on the flywheel is slightly past the magneto

* The cam is aligned so that both valves are down and the exhaust is the next to open.

What am I missing? It’s like the engine in 180 off but I can see no way of modifying the way it is set up. 

Thanks,
Fred


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## roperdude91 (Nov 10, 2004)

flywheel key, simple but overlooked problem


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## bugman (Aug 12, 2004)

yeah if you broke the connecting rod, and the key has just the slightest indention in it, needs replacing, and the old one will cause em to backfire out the carb. also gap the mag with a dollar bill, best way to get good spark out of em.


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## snowdog88 (Apr 28, 2005)

You got it guys!!! 

I didn't think that would be it but that was the only part that I hadn't checked. Sure enough, it was sheared in half. 

Thank you,
Fred


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## bugman (Aug 12, 2004)

good, it is a constantly overlooked problem, most of the engines thrown away today, is on a count of sheared keys.


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## kkbrnh (Aug 10, 2006)

I was having the same problem. Found the key sheared then relaced it . Now it is not even firing .Infact it is acting like the timing is way off. Any suggestions. Thanks!


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## MowerMech79 (Jul 6, 2013)

Above: assuming you have reassembled everything properly and adjusted your valves with the piston on its compression stroke at TDC (top dead center), there is one item that is constantly over looked.. Spark Quality: Most people check to see if there is spark, but not all spark is good spark. Especially if the engines ignition coil/module is aged. I recommend using a new plug, and closing the gap just a tad past manufacturer recommendations for aged coils.. also, check the gap on your ignition coil in reference to the flywheel. A business card can be used in a pinch, but .010"-.020" feeler gauge is my recommendation.


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## 30yearTech (Sep 14, 2006)

Hello MowerMech79 and welcome to Hobbytalk. Did you realize the post you are responding to is 6+ years old?


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