I have a new DA 120 that is going lean in flight after 1 to 1 1/2 minutes .
( Doesn't exhibit symptoms on ground run ups.)
Note the aircraft is strait and level at about 1/3 to 1/2 throttle when it goes lean and dies.
I have checked fuel lines for leaks, fuel filter, tank vent line for obstructions ,diaphragm vent mod doesn't change any thing, and just for fun replaced all components on ignition . ( battery , switch,optokill , regulator, ignition.)
I know the ignition is not making it go lean but had the stuff so I changed it.
Any ideas as to what I'm missing ?
Thanks
Josh

Is the engine baffled? Overheating? Check that the line to the pick-up clunk, is actually the one connected to the carb. Will it run on the ground, and power up? I'd probably richen the lo needle 1/4 turn to see if that helped.
zx32tt

What type of airframe is it? Large cowl, like a Yak or smaller like an Extra. that can play a large part in cowl pressure affecting the carburetor diaphragm which will make it go lean in flight.

Sorry I a must of skipped over the part where you said that you did the diaphragm vent mod.

Since you've checked all the tank plumbing, move forward to the carb. Take it apart, clean it and assemble it. Check the pulse port on the manifold to make sure it's not plugged with sealant, and inspect the reeds to make sure they're not leaking or cracked and assemble. Look for potential air leaks at the reed block, manifold and carb joints.

try opening the low end a little

Cowl is baffled . Runs fine on ground. (May lean a little at part throttle on ground after a minute or so.)
I have cleaned and inspected carb.

Sounds to be over heating, What temp is it running in the air ?

Not real shure . Motor is barely warm on landing after it quits in air.

Motors can cool as much as 175 degs on landing approch. If you're not sure I'd get a temp gadge and find out before you burn it up.

Try going richer. Just because it runs good on the ground does not mean it will run good in the air. Probably just needs some fine tuning.

Going richer may help but it could also mask the real problem. Then you have a motor that runs rich just to stay cool. get a gadge and tune the motor again.

Couldn't the reeds cause an issue like this also?

which cowl? and which carb vent mod are you using? not all carb vent mods are created equal. what oil are you using at what ratio? sounds like the vent mod is not doing the trick, and you are lean in the air. its possible also that you have an air leak in carb area thats leaning it out. check your block and carb and make sure everything is tight. pull your needles out and clean the seats, trash in the needle seats can cause weird stuff like this. make sure, you are running a fuel filter on your gas can and another on the plane between tank and carb. a filter clunk would do the trick here. good luck finding the problem. most of my deadsticks on DA's have been attributed to HEAT. they dont like being run hot or lean.

i think reed damage would cause it to run rich and not lean.......maybe im wrong but thats what im thinking.