Bahh.
One can ' dampen ' it , just like a stunt Engine . As in prime , turn thru ( belt over then belt thru backward , 1/2 Doz. Ea. ish )
THEN Fill the Tank , Unless youve got a CLAMP on Both Lines . Or at least the PRESSURE LINE .
Battery ON , Belt & remove Clamp as it starts .
What the bugbear could be is Flooding It thru the Pressure Line ( it usually is . So this is what you wanna watch . AND is why you keep it shut
at least till your ready to flick it . Trial to see if that or release as / when it starts . Usually a second delay - ish .
Also a ball valve in the pressure line may mean you Just Start It . As it cant backflow and flood the crankcase ..