The other thread about the MightyVac got me thinking about sharing a bench tester I built. Doing a pressure and vacuum test on a a two-stroke crankcase is a pain to do but it is so necessary to verify that the crankcase integrity is good. A small leak, or even a big one, is easy to mask by adjusting the carb, but it is still there and will require constant tuning to try to keep the engine running right, since the leak is affected by barometric pressure, humidity, and temp. I have had engines that were leaking so bad that it was hard to pump the hand tester fast enough to find the leak. Another tech. gave me the idea for this so I built one. The idea here is to have this on the bench so that there is no excuse not to do the pressure and vacuum test. The gauge is an automotive vac-pressure gauge from back in the carb days when we checked fuel pump pressure and manifold vacuum. The silver block in the middle comes from an air driven evacuator for air conditioning that I bought from Harbor Freight on sale for $7. To use this, block off the engine in the usual manner, and attach the hose from the tester, and for pressure testing, open the bottom valve while leaving the other two valves closed, then slowly turn in the regulator to bring the static pressure up to about 10 PSI. Then close the bottom valve and the pressure should hold. If not use soapy water to find the leak. For the vacuum test, leave the bottom valve closed and open the top two valves and slowly turn in the regulator to indicate about 8 to 10 negative PSI. Then close both top valves and the vacuum should hold. ALWAYS BACK OUT THE REGULATOR BEFORE USE SO YOU DON'T DUMP PRESSURE INTO THE ENGINE. The silver block is a venturi vacuum so when air is going through it it builds negative pressure, but it is noisy, so that is why I put a valve on the regulator side, so I can keep it turned off. Here are a coule of Stihl muffler spacers I use for blocking off the exhaust, which is much easier than using the muffler shell to hold the rubber flap in place: This is the 1123 block off plate, which I modified to use on both the 4180 and 4282 Stihl 4-MIX engines when testing them: I use dish detergent in a squirt bottle for finding leaks. I haven't tried it but someone said the bubble mix the kids use works good, so I am going to try that next time. I also use this tester to check fuel tanks on hand held equipment. They should always hold pressure, and always leak under vacuum. I use the vacuum feature to draw negative pressure on a 2 gallon plastic fuel can with 2 fittings I placed on the top of the can. Now I can evacuate the fuel from the tank for reuse or just to get it out for storage of the saw. I use a second can in the same way to draw out bar oil. QUESTONS FOR DISCUSSION: Which should you do, vacuum or pressure, first, and why?