manifold pressure with spring gauge

I just got a used spring gauge that I won on eBay ( this one), and decided to hook it up to see what sort of readings I got.

I pulled the rubber nipple off of the carb mount and hooked up the gauge. When I started the bike, the needle was vibrating back and forth really quickly across a wide area of the dial.

I haven't checked valve clearance (something has to wait for winter!), and the compression is uniformly low (105 PSI) across all cylinders.

Has anyone used spring-type gauges to measure manifold vacuum? Should the vacuum pulse quickly, or remain steady?

Or should I really avoid touching the carbs, even just hooking up a vacuum gauge for fun, until I verify valve clearance and locate the source of the low compression?

that gauge will pulse greatly, if I was going to use it to sync my carbs I would install a valve in the line to dampen the pulses. If this was the only gauge I had to do the job it could be made to work but a multi-gauge set like from JC Whitneys or the bike shop would be better suited to sync'n the carbs than the one you bought.

what you need for that is a pnuematic flow control with barbed ends. i made up a set of 4 regular vacuum gauges and used them to snubber the fluctuations... works great...steve