He tells me: First of all, try to locate wich cylinder is faulty. When hot, disconnect one of them (spark plug). Re-connect and try disconnecting the other one. Let's see if it keeps running or turn off. If it keeps running with both, then problem is locate "upper" at something that affect both cylinders. If engine culdn't keep running with one of them, tha one is faulty. Then we can take next step.