I read on the saito engine information web site that the saito engine Doenst like to be Throttled Fast.
Information from
http://saito-engines.info/special_tricks.html
As the throttle is quickly advanced from low to full throttle lots of air suddenly enters the engine which will cause the engine to quit unless the low-speed mixture is set sufficiently rich. The faster the throttle stick is advanced the greater is the tendency for the engine to quit. Therefore, if the throttle motion is slowed down the low-speed mixture can be leaned further while still preventing the the engine from quitting when the transmitter throttle stick is rapidly advanced. See the ‘Throttle Setup’ section on this web site; it is best to have the leanest possible low-speed needle setting.
The amount the servo is slowed is a personal decision. Just slow it an amount you consider is the slowest you think is reasonable.
The overall result is a very reliable low-speed engine setting. No matter how fast you move the transmitter stick back and forth the engine will not quit.
Of Course only special radios can control Servo Speed.
Kinda sounds like the low speed needle isnt set right i would try to turn it out 1/4 of a turn at a time. my be it is set just a tad to lean. the engine starves for fuel when decreasing the throttle rapidly.
So turning it out a little bit will give it a little more fuel during the quick deceleration IMO
But i'm sure there Are others that will give input but thats what i would try if it were me. You can always put the needle back to were it was before if that doesnt work.