Gian Paolo,

I'm going to assume that you've already checked the basics: fresh spark plugs, air and fuel filters, etc. If so, then I'd say that this sounds like the "cold-shutdown" problem that was discussed on this forum several weeks ago. In summary, these engines are prone to a starting problem when they were started with a cold engine, run very briefly -- as one might do when moving the car from a parking spot on the street to a driveway -- and then shut down before the engine reached normal operating temperature. After several hours of sitting, the engine is difficult to start.

Apparently, the very rich fuel/air mixture that is needed to start the car is enough to wash oil off of the piston rings, resulting in lowered compression when the engine is started again. Extra long cranking is usually enough to restart the car.

The problem won't manifest itself if the car is run long enough to get out of that "rich mixture" mode before it is shut down. The problem also won't manifest itself if there's not enough time for that rich mixture to loosen up the oil film on the piston rings, so a few minutes or even a few hours may not present any problems.

These are not the only engines to experience such problems. My first experience with this issue was with a Mazda rotary (wankel) engine. Those powerplants are notorious for this problem, and it usually results in a flooded engine with extraordinary efforts required to restart them. From my experience with those cars, I'm going to speculate that this cold-shutdown problem will also be agravated by a weak battery, resulting in slower cranking and less compression during starting.

I may be way off the mark with this discussion, so if you respond and say that you didn't shut down the car with a cold engine, then please excuse my ramblings.

Either way, let us know how you're making out with this problem. Good Luck.