Ambiant conditions effect on air fuel ratio

I think you may have to give further details if you want a good response.

In the mean time -

Petrol engines require an over rich (choke) air fuel mixture when cold starting.

If the choke system is not operating correctly, your engine may cold start better, when ambient temperatures are higher.

Wow. Where do you live where it’s 35 degrees Centigrade in the morning? What are the midday temperatures?

Cant speak for Naveed - I live in NSW Australia - in summer we can have overnight temps in the 30's and days up to 46C. So morning temps can easily hit 35 on their way to the mid 40's by mid day to mid afternoon. I did spend time in the British Isles (great pubs, good craic, miserable cold place, less said the better)  and in Alberta, Canada (ultra polite people, great summers, horribly long winters, down to -45C) Give me heat any day.

Definitely check the starting carburetor ("choke") activation.  A friend of mine had this problem because he did not realize that the cable from the activation lever in the cockpit was binding and thus the levers on the carbs were not actually in the "on" position during cold starts.

I live in southern Arizona in the US and we can see those temps also. It shouldn't be causing any starting issues. We have tons of aircraft here and tons of Rotax. No one has issues. Look for a different starting issue.