Motorcycle Repair: 1985 yamaha maxim carb synch, intake leaks, vacuum gauge

Question
I'm having a difficult time with the carb synch. I hook up my vacuum gauge and try to idle it at 1k but the gauge just jumps all over the place until i increase the throttle. When i think i have everything even, I'd do an idle adjustment but it will idle too low and then jump to between 5-7k on my tach. I'm at a loss on what to do.

Answer
When RPMs surge like that on idle it usually is caused by one of two things: intake leak or idle mixture is too lean.

You need to check for any intake leaks (some people spray wd40 and look for a drop in the RPMs).

If there's no leak then you need to richen the idle mixture and drop the RPMs down to 1-1.5K

Once you have a steady idle you can try to sync the carbs.

Before doing a vacuum sync I usually approximate the carb sync by shining a light down the carb body and looking at how much light shines along the throttle. This is usually enough to get the bike idling well enough for a real sync.