On my DA50 with 2.5" standoffs the choke butterfly barly clears the mounting surface. There is about 1/4" between the mounting surface and back face of the carb body. To get it to run properly i've drilled a 1" diameter hole in the mounting surface of my test stand behind the carb to let the engine breath through. Is this a common practice to have to put a carb breather hole through the firewall on rear intake engines? For my aircraft i'm going to run the 3" standoffs to fit my particular installation. This will leave 3/4" clearace between the back face of the carb and the firewall. Will this be enough or should i add the breather hole too? In general, what is the optimum clearance between a rear mounted carb and firewall.

Thanks,
Pete

About an inch. The carb cut out in the firewall is a pretty common way of resolving the distance requirements. Good luck with the 3" standoffs....

I have a DL50, but the same applies. Mine is mounted in a GP Patty Wagstaff with the supplied standoffs that just barely allow the carb to clear the fire wall. Apart from the hole in the fire wall which allows me to run the fuel line etc, I've made no other adjustments and the engime works fine. I should think that when you change to the 3" stand offs you will have no issues.