Thanks Mr Cox. This 15LA is new from Tower Hobbies, no alterations have been made except for sealing the back plate and carb with RTV. The pressure nipple is clear, the muffler seals well to the exhaust port and pressure at wot is approx 1 psi. At idle the tank pressure is too close to zero to accurately read on my 15 psi gauge. I have a new 5 psi gauge on order, should be here soon.<br /><br />My assumption is that once any rc engine is brought down to idle the tank pressure will drop to near zero psi within a few seconds. At idle fuel should be drawn by virtue of crankcase vacuum alone should it not? Older rc engines didn't even have mufflers.