Best jets for 914 in open air

Hi.

I have a 2007 914 in my MTO Sport gyrocopter.

And it's mounted as an uncowled pusher - so it has a lot of cooling air.

When I bought it, it had 432 on the Hobbs. last year I overhauled the carbs -

not knowing if they needed it, but the logs are sketchy. It now has 700 on the Hobbs.

The main jets were 152 and 156, respectively.

The new jets in the kit are in the 16x's. I was told, they are nowadays larger for a cowled engine.

I always let the turbo cool down at least 2 minutes.

There is a lot of soot on the outlet of the after muffler and on the rudder.

I noticed on another 914 (cowled) gyro the after muffler outlet was light grey.

Shouldn't my outlet be the same colour?

I should add, I have washed and oiled the K&N air filter...

Regards,

Erik