Callin the Cap'n or other engine Yodas, Manifold vacuum gauge readings Options

[ThePaintedMan]

I took the advice of a few folks on here and finally got around to buying a quality vacuum gauge. As a primer, I've had all kinds of issues, from carb synching, timing, etc. But I think I've finally got it running fairly well. The car is a '73 with a 1.7, dual Weber 40 IDFs.

Anyhow, I did a compression test the *right* way this time with the throttle open and after the engine was warm and got 110 across the board. Not great, but not awful. Next I moved onto checking the vacuum on each manifold port at the base of the carbs. I get wildly, but consistently fluctuating numbers on each cylinder. By that I mean, at idle, each cylinder displays the same thing - the needle bounces from 5-17 mm Hg instead of a steady number. I've been reading up on this at:

http://www.thesamba.com/vw/forum/viewtopic.php?t=476817

and the great animations at:

http://www.therangerstation.com/Magazine/S...VacuumLeaks.htm

Is it then possible that I have FOUR burned exhaust valves? I had been suspecting I had at least one for awhile, due to seemingly high CHTs on #3, "sucking" coming from the tailpipe and the fact that #3 doesn't suck nearly as much air from the velocity stack as the others. But now I'm suspecting a larger issue. Is it possible that both heads are loose? I see some oil leaking from the cylinder-case junction, but don't see anything from the head-cylinder junction. Would it be worth taking the in off and trying to retorque all the head studs, if nothing else, for piece of mind?

-George

[Dave_Darling]

The instructions you're following are for a system that has a single plenum that feeds all of the cylinders. Like the stock fuel injected system does. With the Webers, you're only seeing the vacuum for one single cylinder, and that will vary a lot. If they all behave the same way across the board, chances are that the vacuum reading is normal, or at least close to it.

--DD