Dang Harley, Your really going to town helping the OP out by giving him some very good advise . Quite a change from your usual one liner replies. Keep it up your doing real good .
To the OP . Don't let some of these guys intimidate you about buying tools especially that Mighty Vac . It is a must have for fixing saws correctly. You can save money by testing different systems on a saw with one. Those parts may be small but they add up if you just spend money on parts you may not really need. Sometimes new is not always the best fix. If it ain't broke don't fix it.
You don't need the top of the line MV. They do make basic models that come with the tips to do pressure / vac tests. I bought a 8500 and it didn't come with as many tips as the cheaper one I first bought . Just a word of caution don't let gas get sucked into one of those M/V . I like to use lines I can see if fuel is going backwards into the tester. A gas tank for example may be drained but there is still fuel in the filter and lines .
Pressure/vac testing is just one test to see if your crank seals, base gaskets are leaking. You can test carbs, fuel tank and lines and pulse lines. Other uses for the M/V are brake bleeding ,never tried it myself as of yet. Recently worked on a 4 stroke generator and used M/V to see if inlet needle in the carb seated properly which tested good . Saved me some money and time. I am sure there are more things you can do with one if it entails movement of air one way or another.
Oh, might want to add another tool a hemostat or roach clip (70's flash back ) to pinch off fuel lines or pulse lines if you need to test them . Another must have tool and is cheap. Handy to have when your changing a fuel filter which you will probably be doing .