I have a B&S 4hp lawnmower that I had to replace the magneto. The spark plug wire got a slice in it causing a short. Well now it kicks up and starts but only after priming (it runs two to three seconds).

My question, what is the best course for trouble shooting? I changed the plug already. and it is getting fuel, The plug is damp when I pull it.

Could the gas just be fouled? the gas is about a month and a half old.

Or did I position the magneto in correctly when I mounted it (how much of a gap from the flywheel)?

Thanks for any advice this site has been invaluable to me.

ok, the magneto, ( this side out is out ) of course you won't get anything if it was the other way, gas doesn't get fouled, but gets rancid...., it'll cause hard starting, but if you smell the gas, you'll tell if its good or not. it'll have a totally different smell then fresh. i like to gap the magneto with a dollar bill, till the bill slides out with friction on it, but doesn't tear, then spin the flywheel to make sure it won't catch. if this doesn't do anything.....was anything hit that brought it to a abrupt stop? could be the flywheel key if it was.

oh and your plug can get gas fouled, so make sure its dried off. gapped at .30

Ok thanks I thought the gas smelled fine. So that's one check on the list. I did get the magneto mounted the right way. I will regap it like you said maybe it just isn't getting enough juice to get a big enough spark when the fuel mix is below the prime point.

I will also make sure my plug is properly gapped and get back to you.

The reason it stopped was from me stopping it but in the mean time...
because the spark wire wasn't in the groove the starter hood cut the line enough to cause a short. so I was just getting a sore shoulder and no spark.

Any recomendations on spark brand? I've been using champion. maybe I got a bad plug.

ngk's. autolites, both are better then champion. do you still have the old plug? try it

Check the timing. make sure the flywheel key is ok and the exhaust valve is not stuck shut. also, check for a clogged muffler. all of these will cause the exhaust to go back into the carburator and cause it to stall.