Basics for problem solving. Look in front of your nose

I bought a second-hand Vespa in September 2008: summer was over, temperatures were gently dropping and hot nights were just a memory. I spent the whole autumn, winter and spring driving to and fro through Madrid. When summer was back again and I was going back from work one hot day in June, after around 7 Km and almost at home, the engine switched off while I was in the middle of the street. I got scared, I pushed the Vespa to the pavement and tried everything to kick start the engine. I had no success, then I put the helmet off and started reviewing the basics.

I know almost nothing of mechanics, but at least I know that the spark plug should receive electricity, you need gasoline, and besides gasoline, the oil tank must be full. My Vespa is vintage style, then it has a two-stroke engine. Maybe not everybody knows that two-stroke engine gets fuel from two deposits, one for gasoline and the other for oil. Maybe you have noticed those old motorcycles, mopeds or even one of the first scooters expel dense smog. Gasoline mixed to oil is the reason. That's obsolete and polluting technology, but things were this way.

I could not manage to find out where the problem was but after some minutes, ready to push the vehicle back home, I tried one last attempt to start the engine and by surprise that worked! I put the helmet on and quickly drove back home. Then, the same story every single day. Almost at home, at the damned Km 7, the engine switched off, and you know the rest of the story: wait minutes and the engine could start again. I tried everything to fix the problem but without any good result. Mechanics had no idea and neither did I.

• I had some electronic components replaced
• I reviewed petrol tank cap had the typical hole to let air through it and avoid vacuum effect (you know, pens have that small hole for the same reason, to enable ink flow)
• I replaced the spark plug
• I cleaned the carburetor and its oil and air filters
• Meanwhile, I replaced the whole engine for other reasons

The damn Vespa got stuck at Km 7. And during four years, from June to September I was condemned to switch the engine off whenever possible, for instance when waiting at traffic lights. I knew it was something related to hot temperature, but nobody could imagine how, having replaced almost everything of the original Vespa.

This was the routine until few weeks ago. From one day to another, my beloved Vespa started behaving fine and even with torrid climate I could drive home without any further problem. What had happened? I tried thinking of what I could have done, but nothing unusual, except refilling gasoline tank and ..Eureka! I had replaced the usual brand of oil, one of the cheapest for an expensive one!

The oil I had used to refill my Vespa until that day was cheap and low quality and when the moment to refill the tank arrived, it was temporarily out of stock at the shop. Then I was obliged to go for the expensive brand. The solution in front of my nose during four long years, but nobody could have imagined that when in Madrid it is so hot, you need quality and performing oil to have your engine survive.
This experience suggests me to make sure of the following when troubleshooting a problem. 

1. Split the problem into components (plugs, filters, gasoline, light bulb, oil..)
2. Find out components you have been interacting with recently (oil, wrong oil was my mistake)
3. Play with the component (that is: clean it, replace it or whatever comes to your mind)

Before studying complex and expensive solutions to your problem, look in front of your nose. Habits hide things efficiently and insidiously.