Ambiant conditions effect on air fuel ratio

Hang on Roger, are you saying you don't use choke for a cold start when your ambient temps are under 30ºC?  

He has no problem starting when it's hot, his problem is when it's a bit cooler.

Dear All, thanks for your replies. 

Naveed wrote:

Dear All, thanks for your replies. 

Hay Naveed - were our comments of any assistance?

I always use the choke on the first start of the day. I've never had starting issues with my planes except when I had an older Rotax 912ULS I had purchased on a Kolb aircraft with the old black starter and the fact someone had installed a too small a battery. As soon as I changed the starter to the new style and a bigger better battery all my starting issues went away. If I just landed and restart in let's say 15-45 minutes later I don't use the choke. Depending on where your idle rpm is set I would also crack the throttle. Higher idle rpms no throttle, low idle rpms I crack the throttle. In Arizona we can see 25F  temps in the winter and temps up to 115F in the summer. Starting in the warmer weather isn't usually an issue, but the cold temps can be and if you live in cold temp country then an engine pre-heater is a good thing to have installed. All the people I know that fly and my clients use the choke on first starts. Most all of them have idle settings at around 1700 rpm and Vans RV12 factory sets their idle rpms at 1650. You should never sit and idle that low. During warm up everyone I know warms up between 2000 - 2400 rpm. I have approximately 4700 hrs. on Rotax engine powered aircraft.

I too always make the first start of the day with choke, but on really warm days you might not need to.  I was asking Naveed if he was sure that his choke was actually being activated on the cooler days when he was having trouble starting.  Just because you pull the lever in the cockpit does not necessarily mean the choke is being activated at the carbs.