I have a SIT unit that smokes well, but does not generate as loud a choo-choo sound as I would like it to or other SIT units do. It has an ACG AF piston and cylinder instead of a bellows, which is nice. I have cleared all the holes and passage ways throughout the unit. It has an oblong fluted hole or aperture in the choo-choo plate. I have flipped that plate inside out and rotated it, but that made no difference. It has an original AF metal piston. I've also tried a Gilbert AF carbon-graphite piston and an aftermarket plastic/Delrin piston. The AF carbon-graphite works a tiny bit better, so I'm going with that. What else do you suggest I try to get it to choo-choo louder? Is the correct orientation of the plate such that the lip or fluting of the oblong hole is at the bottom (see photo below)? I've also seen some plates with a circular hole with a raised edge all the way around it. Did those come before or after the oblong hole? Do circular-hole plates generally work better (sound louder)? This smoke unit casting also has an open top and bottom primary or first chamber (see photo). I've worked on others that are cast shut at the bottom. I covered the bottom of this one, but that did not make the choo-choo louder. Thanks.
PS You'll notice also this unit has a metal drive gear instead of the usual fiber gear.
