I test ran one of my two MARZ 2.5 engines this weekend. It didn't take too long to get it to run. But after a few tanks of fuel, two of the head screws stripped out and fell out. On the last tank of fuel it was running pretty badly and surging like crazy, and had developed a need to turn in the compression screw more. That was when the head screws came out. I killed the engine and put the screws back in and then discovered that they had stripped out. I am hoping that I can drill them out for the next size up, which ought to be a 4/40 size SAE screw a they look like they have 3mm head screws. Hopefully whoever made the engine years ago, had done a poor job tapping the hole or they over torqued the screws down, and it isn't a poor alloy casting. Anyway that might help explain some of the messiness the engine exhibited when running. I thought it was just the oil oozing out around the exhaust collector ring.

The other Marz 2.5 engine had loose or bad bearings right out of the package. I haven't taken it apart yet to pull the bearings out so I can see what I can get to replace them with. But I'll have to check those head screws out again. I think on both engines I'll replace all the slotted screws with hex screws anyway. Those little slotted screws on the head aren't easy to loosen and tighten without tearing up the screw heads on them.

I also want to see about rotating that exhaust collector ring so that the exhaust output is not coming out right on top of the needle valve, as your hand gets all oily off the exhuast adjusting the needle.

I was getting almost 14,000 rpms using whatever that special Russian Prop is that came with the engine. Yeah I know real dangerous.