I too tried the RHB-31 with a 38MM mikuni in suck through configuration on a single cylinder. I would like to know where you acquired a RHB-31 from.
Like others have said, I have experienced first hand destroying the turbo due to oil seal issues, and would suggest running both a separate supply pump and scavenge pump with a separate reservoir for the turbo. I also firmly believe as others have said, that a single cylinder does not lend itself to turbo'd applications because the exhaust pulses are too few and too weak to really make the turbo shine, also consider the pulsations occurring when the intake valve opens and the cylinder is charged, some have suggested a plenum that is at least as big as cylinder volume, of course this leads to the inherent drawbacks of fuel mixing etc with a suck through system, we also tried a BIG turbo on a small 2 cycle and came to the same conclusion that a turbo hurts naturally aspirated performance on small displacement single cylinder engines.
That being said, I intentionally ran the motor way rich, and WFO throttle was the worst performing area by seat of the pants feel, feels like the motor is way too restricted, which it probably is by exhaust backpressure, (using a factory cam). For the fire out of the dump pipe, try retarding the timing a bit, and watch for the turbo oil seals to go away. Install an O2 sensor with meter in the header pipe and take it out for a spin, be leery of plug checks because of oil contaminating the intake charge.
In a perfect world, a blow through, with intercooling and big plenum, is the way to go, but still think the exhaust issues are relevant with a single cylinder
Hope it helps