After tightening the throttle spindle clamps you should check the air-flow
again at about 2000 rpm - it is more important to get the flow balanced when
running than when idling. In my experience of running various cars with a
vacuum gauge permanently connected, and occasional use on the MGB, I would
expect closer to 20 than 16. But that was always with ported vacuum,
although I wouldn't really expect manifold to be any different.
PaulH.
----- Original Message -----
From: R. O. Lindsay <rolindsay@dgrc.com>
Cc: <mgs@autox.team.net>
Sent: Friday, May 18, 2001 3:13 PM
Subject: Vacuum
> I loosened the clamps on the linkage so each carb
> operated independently then balanced the air flow using a
> UniSyn <I think it was once called> until the flow rate was
> equal at 800 rpm. I revved the engine just a little using one
> carb then the other noticing that the engine settled back
> down to 800 rpm and that the air flow was still synched. I
> then locked the linkage and set off on adjusting the mixture.
> With a tachometer wired to the coil and a vacuum gauge
> connected to the inlet manifold, I adjusted each jet-height
> nut up and down observing changes in rpm and vacuum
> until I maximized the vacuum at 16-17 in Hg with the engine
> speed still at 800 rpm. The little bugger sure sounds good
> now and leaps to life when the throttle is cracked open.
> My question is just this; What manifold depression do
> you measure on your MGBs? A wonderful old book called,
> "The Sports Car Engine - Its Tuning and Maintenance" by
> Colin Campbell, says that a nice healthy MGA should pull
> 18-19 in Hg but does not list the MGB <as the book is a
> little too old>.
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