Hi group from Nova Scotia. My 3.5 hp B&S will not start. When it does try to start it backfires though the carb. and muffler. It gets fuel when I prime it, spark seems to be ok. Took the carb. off and cleaned it the best I could, unless I'm missing something which is quite possible :) My father-in-law has the same model so everything seems to be hooked up ok. It was working great until the person who borrowed it brought it back with the carb. loose but said he didn''t loosen it {right}. Any suggestions would be appreciated.
Rene

ok, backfiring through the carb? sounds like the key may be sheared. since most won't tell you if that mower they borrowed hit something or not.... i'd go ahead and have the flywheel pulled and the key checked, fairly easy and simple, keys are dirt cheap. and if its of any age, replace the diapragm and gasket. they are pretty cheap. make sure the diapragm don't get folded and you put it on wrong.... and just as long as the carbs screws are nice and tight, that should do it.

take a good look at your blade and crank shaft also. the carb being loose could mean they hit something and bent the crank or blade thus making it vibrate things loose. kinda like a harley. :)