The first start of the day
 

I've noticed this behavior dozens of times over the last year and am wondering what the cause is: Starting my OS AX engines for the first time on some days, the engine will start, but it will not take throttle at all and will falter or stall with the glow plug driver still connected. (It will run at idle or low throttle but you can tell it is lean.) Choke the carb with your finger just a fraction of a second and it enrichens and runs normally and can immediately take a more wide open throttle. What causes the "first start lean syndrome"? Note that I rarely touch my needle valves unless the temperature has changed or if I am tapping a new gallon of fuel. By the way, this syndrome never happens on later flights, only on the first flight of the day. I have never noticed any bubbles or air in the lines when having this situation. Any ideas on why a quick choke while it is running clears up the problem?

RE: The first start of the day
 

Oil residue/gunk partially blocking the very fine and narrow passages in the needle assembly that is washed away as soon as fresh fuel is passing through??

RE: The first start of the day
 

I think the engine just needs to warm up. Engines need a richer mixture when cold because less fuel vaporizes and mix's with the air.

RE: The first start of the day
 

X2

When an engine is stone cold it will run lean. Even when an engine has cooled down between flights, most likely in direct sunlight, it is still not as cold as an engine that has sat idle, most likely in a shaded place for 24 hours or more.

What OP was experincing indicates that his tune is spot on. If it didn't exibit these syptoms, the tune would most likely be a bit on the rich side.

Nothing to be concerned about.

RE: The first start of the day
 

It is common for our engines.maybe oil residue at muffler nipple may cause this or thicker oil residue anywhere but its normal.

RE: The first start of the day
 

I must err farther on the side of caution with my engines because whenever I start mine up they're always rich. If its colder out than when I last ran the specific engine, I'll richen the needle 1/2 turn before first firing it off. If about the same air temp, I leave it alone until the engine warms up.

I use ambient air temp as the judgement factor as to how the engine is going to run from dead cold.

Thats just me though..

RE: The first start of the day
 

Both my engines (Enya and ASP) do this.  My old [real] cars (before elec injection) used to behave like this at first start.  I never questioned why, I just let them all warm up a bit ! 

RE: The first start of the day
 

Appreciate all the inputs and I agree that the engine is operating stone cold and not in a normal condition. It takes such a short choke with a finger on the carb to clear it up though, and the temperature can not rise that fast. Could it be that the crankcase needs to have a residual amount of fuel to scavenge it correctly? (The quick choke on the carb might give it this bit of extra fuel.) I normally run my engines dry at the end of the day, and don't normally put in after run oil.

RE: The first start of the day
 

I normally run my engines dry at the end of the dayhttp://www.dvxs.info/1a8.jpg