I wanted to share this leak down tester I made after seeing one on youtube. Its a hell of lot cheaper than the $200 or so leak down kits that are out there for sale. You can get a 0-15 psi liquid filled gauge for about $10-$15 and then another $10-15 in fittings. It would have been easy enough to put an air Schrader valve on the end but I didn't have a tire pump and did see an old blood pressure cuff up in the closet. They even sell gauges attached to a brass block with a Schrader already on there for $12 on amazon but I went with what was available at the hardware store. I wouldn't use a compressor to fill the engine because I've heard you can blow out a crank seal. You need to remove the carb and exhaust.
The end of it that goes into the intake boot is marked as 1 1/4 but the outside measurement is 1 5/8 which fits perfect in the boot. The expansion plug for the exhaust port is marked 1 3/4 and you have to crank it in there tight (I hold the outside brass with channel locks and then ratchet the 13mm nut down) and make sure you wipe the oil out with brake cleaner when you take the exhaust off or the plug will shoot out when you pump up the engine. The engine should hold 6 psi for 6 minutes. If you're losing pressure spray soapy water on the engine and look for bubbles. Also spray the tester to make sure its leak free so you're not chasing your tail looking all over the engine (like I did).
Edit: Peek through the exhaust port when you take off the pipe and make sure the piston is at bottom dead center for the leak down test.