Vladimir - welcome!
2 spark plugs per cylinder - do you know how that ignition system works? I have seen automotive engines like this before, where the second spark plug is meant to fire on the exhaust stroke to help lower emissions. For the engine that I’m remembering, someone determined how to re-route their spark plug leads so that both plugs fired at the same time, so that more of the Fuel burned for the power stroke. I would encourage you to look into that modification for your car now, first, to see if that is possible. If so, make that change, and then increase the spark plug gap. You want to burn ALL of the air-fuel charge INSIDE the cylinders for the highest fuel economy and most power and lowest emissions. Little modifications like this help the Groove do exactly that, and in your case, I’m optimistic for significant improvements.
Good luck, and please start your own topic/thread on the forum with pictures (or video, preferably) of your engine and the modifications you make.