My neighbor stopped me a couple nights ago and asked if I had any starting fluid. I asked what for and he said he was having trouble with his lawn mower. I grab a can and head over. He says that the lawn mower has been trusty and started every year since they had it on the 2 pull. He then says I put in fresh gas and a new plug. So I watch him pull it a couple times and nothing... So I pop the air filter cover and I see the air filter.. Holy hell! Its black, oily, full of grass and other nastys and complete junk. I toss it to the side and said you need to buy a new one. So I spray the starting fluid and nothing, not even trying to fire. He said he would let it sit because he thinks he flooded it. About 20 minutes later I hear him pulling away and nothing. He yells over and asks me if I would look into it. I said sure when I had time and he pushed it over to my garage.
Fast forward to tonight, I finally have time to look into this thing. First think I do is pull the plug and check spark.. Wait.... This plug is just as black and oily as the air filter... From what I can tell its still the original plug, but why all this oil? So I clean the plug the best I can and put it in the boot and pull it over. Good bright spark! Good, but wow is that plug nasty, and no way new. So I put that back in and pulled it over. It fired and popped and kicked a few seconds and died. Im thinking the carb needs to be cleaned. I proceeded to take that down only to find a odd plastic carb body that Briggs is starting to use with no adjustments and not much to clean. I get it off and drain the gas out of the bowl and my fingers are oily... I check the gas and he has mixed gas in this thing, which explains the black soot on the paint, from years prior and probably why the plug is nasty. The carb looked good and clean so I put everything back together, dumped out the mixed gas and put in straight gas. Tried starting and nothing but a couple small pops and a backfire through the carb. I pulled the plug cleaned and repeated about another 5 times. Still nothing.
So my question, and I've never seen this. If a plug shows spark could that change once installed and under compression?? The plug is always wet when I pull it so I know its getting gas, but doesnt even want to fire. So Im going to stop and buy a new plug tomorrow after work, but kind of stumped why its not firing. I have good compression and seems to be getting fresh gas now.