On Wed, 21 Aug 1996, Will Zehring wrote:
> I assume my vacuum advance works fine as the timing mark does indeed advance
> when I rev the engine. I'd estimate that it advances another 15 degrees up
> to about 4krmp and then doesn't go any further at higher rpm. This is all
> eyeball-o-metric as we in the science business say, so... ICBW (I could be
That's not vacuum advance, but centrifugal advance.
The way you check vacuum advance is to disconnect it, and plug the hole to
the manifold. Observe the timing. It should be in the 10 to 15 degree
range. Re-connect the vacuum advance. The timing should jump ahead 5-10
degres at idle.
Vacuum advance advances the timing under low-load conditions (like idle
and part-throttle accelleration, trailing throttle, etc.). In the B it is
driven by manifold pressure... open throttle --> no advance, closed
throttle --> lots of advance.
This all assumes you don't have a vacuum retard system as well. I don't
think they were used on Bs, at least not chrome-bumpered ones.
I'd tell you where my car's advance sweet spot is with vacuum advance
disconnected... but it wouldn't make any sense (it's like 30 degrees!!) I
think my harmonic balancer has slipped and the marks on the outer ring
don't line up... or the laws of physics are temporarily suspended in my
engine.
I'd open it up and re-time it, but some friendly tourists backed into it
on Monday with a new mini-van, and crumpled the hood. I'm too scared to
open it, as it may not close again before the body work is done. And I
have to get to work every day...
John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
mushed actually works now no catalytic conv or clutch
"E Pluribus Modem"
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