In my 1991 Peugeot 309 when it's colder outside, no matter the engine temperature, when I'm driving on low revs for a while and then add a more "generous amount" of gas the engine just stops responding and then suddenly springs forward violently. Only happens when I'm in 1st gear and rarely 2nd. The engine doesn't stall but I theorize I just overflow the carburetor with fuel. It's a twin-barrel Solex carb, probably factory, just had it adjusted. Strangely I never had this happen on my older cars with Webers, though I know Solex is also owned by Weber.