Haven't run into this problem before, so here goes...
Neighbor brought me his bike, newly acquired but long dormant '75 400F. He got it fired, but it ran like #$%* (and he didn't drop any oil into the cylinders before firing, but did kick it over a few times to try to get oil circulating).
Told him to bring it to me cold, and did a valve adjust, checked points gap and dressed points, cleaned plugs, etc. Timing was close to spot on, so I thought I would do a carb sync.
The carbtune tool showed no vacuum across all four. I'd rev the bike up to 3k or even 4k, no movement, then a quick blip up to 3/4, then back to dead. Adjusting the sync settings could bring up the 1 and 2 cylinders a little, but adjusting the 3 or 4 killed off all reading again. In the end, I could get it to barely hold an idle at just under 1500, with the steel tubes in the carbtune just barely blipping up across all four. The idle speed screw is turned all the way in.
I have a relatively new carbtune tool, and it's been working fine, so it's not the tool (And the idle is an obvious symptom too).
It's got a stock intake with good seals and good rubber all the way around. It's got an aftermarket stainless 4-1 with a baffled muffler on it.
Compression isn't so great: 120-110-110-120 but I am thinking that since it sat it might come up a little, and 120 seems to be OK enough to run and idle in my experience.
Finally -- he did not rebuild the carbs, neither did I. He said he drained them and a little white powder came out. One cylinder wasn't firing, so with the carbs on the bike I removed the bowl, checked the jets and replaced the twisted wire holding one jet in with the proper spring. The bike then fired on all four. So -- sure, rebuilding the carbs could be the easy answer and what I recommended (but he doesn't want to do it... and it's firing on all four).
Any answers on the lack of reading for the carb sync?
