Finally! - some help

I posted a query on the DIYGasTurbines group at Yahoo and got some helpful advice.
(Thanks guys)
It seems I need to really 'push' this thing - as much starter speed and fuel as I can - push it right up to the highest speed I can get.

Before anyone get's excited - I didn't get it going, but I think I got a lot closer and identified a couple of problems.

Taking it up to maximum speed on the big blower and opening the throttle (carefully) to the max, I got over a foot of water pressure in the casing - 0.03 bar. I had taken the tacho off in order to get a better airflow into the intake so speed is unknown - although that pressure corresponds to about 30,000 rpm.

When I tried to remove the blower, I got a huge roaring, drumming sound from the front that I could feel in the air around the air intake. I believe this is compressor surge. In which case, the impeller is unable to handle the back-pressure from the engine, leading to a rhythmic stall-and-recover from the blades.

In a way it's good news. It means the compressor is close to the working region.

I'm going to rebuild the front of the engine, impeller and diffuser, to a slightly different design to give a smoother airflow.