I have 4 of them. I've had them since Royal came out with them. I was a dealer and my cost was 45 dollars. An old OS 40 or 45 needle valve will work. I really like them. I have used these Royal 40 and 45 exclusively for an unknow number of hours. The only trouble that I have encountered is the muffler likes to vibrate off. Maybe I should balance my props but I don't on these little engines. Oh, yes, the ring on one of the heads wore out. I replaced it and whowee. I'm getting around 12,500 rpm with a zinger 10 x 6 wide blade. That's not bad for an inexpensive engine. I'm using 10 % nitro.