I used to have a Thunder Tiger 46ProH in my Raptor50 with a Funtech HN50 muffler which was low on power but ultra-reliable. In over 300 flights, I only ever had one flame-out that was caused by a glow plug that had obviously gone bad. I always ran this on 15% or 23% nitro, tuning was just a matter of setting then forgetting the needles - summer or winter.

I got to the level where the lack of power was holding me back so I went to a YS-50. Initially, I ran it in with the Funtech HN50 and it seemed reliable. I had a lot of spit-back from the carb and it was drinking fuel but I put this down to rich settings for break-in.

Then I leaned it out after around 15 tanks and was disappointed with the power, I was also still getting a lot of spit-back. I looked at the interface of the muffler with the exhaust port and figured that the Funtech muffler was causing way too much back pressure, so I followed a club member who uses a Hatori tuned pipe successfully on his YS. I put on the Hatori 3DII and the power was suddenly awesome and the spit-back disappeared.

However, it has also become a real biatch to tune. I can set the high needle to give me perfect smoke and excellent climbing power, and I can set the low needle to give perfect idling and initial pick-up, but the mid-range is awful. I have now notched up 5 flame-outs, one of which resulted in a massive boom-strike due to a too-low entry into an auto. In every case, the flame outs have occurred when bringing the throttle back up from 30-40% up to 60-70%, typically when transitioning back to hover. Initially, I was running on a governor, but I have temporarily disabled that to try to troubleshoot the mixture. The needle settings are ultra sensitive between too lean and too rich. plus / minus two clicks on main takes it from over-rich (almost four stroking) to over-lean (power fade). The low needle only requires about plus/minus 5deg rotation to be outside of where it will run at all like it should.

Conditions and checks to date are as follows;
Airframe - Raptor 50, 600mm rotors and standard 8.5 gear ratio
Ambient temp - 28 to 35degC
Altitude - 600m asl
Plugs used OS#8 and YS#2
Fuels used IM Pro Glow Max (Japan) 23% and 30% both with 18% oil
Fuel tanks - removed and checked for pressure leaks (none found)
Clunks - replaced in main and header.
Fuel Filter - clean (tried with and without)
Crankcase check valve - is fitted as per the manual.
Pressure regulator / carb - stripped and cleaned it twice

On an OS#8 and 23% nitro, it is almost impossible to get the engine to transition onto the high needle, just cuts out on the ground.

Now on the YS#2 and the 30% nitro it will just about keep running, but pick-up through the mid range is still very iffy and in flight transitions from FF to back to hover continue to be a very nervous experience. The engine is missing frequently in these low-load, mid-throttle settings.

I am by no means an expert on tuning, but I have tried to follow the manual and logically adjusted for every combination of settings possible - the damn thing just won't transition reliably whatever I do.

I am now removing the engine and going back to my trusty old TTPro46H for the time being. Maybe if I put the Hatori on that, it will improve the power anyhow.

But, the YS is a big disappointment, I had read so much about how they are easy to tune and stable running. I am about to pack it up and send it back to them for a thorough checking - but I thought I would pick the brains of the guys here first to see if there is anything I might have missed.

Th only difference we can see is that my buddy at the club has a slightly older model with the screw on the pressure regulator. Mine was bought this year and had the solid style regulator.

Sending it back was the best move.
The YS has a carby like no other. There are passages drilled in the carby itself that work very different to your normal venturi carby. I am guessing that one of these is blocked by maybe a sliver of swarf during manufacturing. Yours is way too touchy in the transition range. But one of our greatest problem fixer has always been the Enya #3 glow plug. Countless engine problems in tuning have been fixed with this plug. I don't think the plug would fix your issue, but it would be worth while having in your tool box for when the engine comes back.