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You should definitly get a vaccuum gauge. They are the quickest way to judge the condition of an engine.
Theres three different kinds of vacuum: throttle, ported, and mainifold.
Throttle is before the butterfly and (I think) should be 10-15 inches Hg at idle( the amount mercury rises due to vacuum in a calibrated tube) and 18-22 at WOT(wide open throttle).
Ported is taken right next to the throttle. 0 at idle (becuse air is going through the bypass) and 1-22 at WOT. The EGR is run off this, but must also go through a wax pellet thermal switch so there is no hesitation on warmup. Vaccum is also stored in vaccuum amplifiers (don't ask me about the 79 accord which looked like a bowl of spagetti under the hood).
You should check a vacuum routing diagram if possible to make sure there isn't something holding back the vac.
Manifold is after the throttle body and the most important. It should be 18-22 at idle, 0 at snap open throttle, and jump up briefly to 40ish on snap closed. The engine is an air pump and you can check how well it works by taking a reading from the brake booster hose (or another if more conveininent)
In short:
A low reading(16in) could mean late ignition timing, a stretched cam-chain or a worn engine.
A wandering needle could be vacuum leaks or fuel flow problems
A rapidly bouncing needle could mean a bad/sticking/misadjusted valve.
A slowly dropping needle (from throttle vac) could mean clogged exhaust.
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