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Posted: Sat Jan 06, 2007 12:53 am
by katanaman
Maybe if Phil sees this he can explain what the MS extra software does with advance retard. MS only sees full vac via the map sensor so it would be interesting how they worked it out.

Posted: Sat Jan 06, 2007 2:30 pm
by GreenV8S
Paul B wrote:
GreenV8S wrote:
Paul B wrote: Is this the one by perchance
That's the one, well worth reading.
I thought it clarified a useful bit of much-misunderstood information, but I'm now not too sure about using manifold vacuum in all circumstances as it appears to have been the cause of the erratic misfire at idle that has plagued me for a year or so. I'm pretty sure it has gone away every time I've disconnected the vac advance.

Even after fitting a different dizzy and a brand new carb and manifold system it was still there, but removing the vac advance 'appears' to have cured it. I now run it on timed/ported vacuum and it seems smooth as silk.

I've not had it like this for many miles so it could be (yet) another wrong lead. :oops:
One side effect of retarding the ignition is that it produces less power (and more heat) so you need more throttle, so you get higher gas speeds, less manifold depression, less EGR and better air/fuel distribution. These effects could conceivably be contributing to your misfire at idle.

Posted: Sat Jan 06, 2007 5:19 pm
by Paul B
GreenV8S wrote:
One side effect of retarding the ignition is that it produces less power (and more heat) so you need more throttle, so you get higher gas speeds, less manifold depression, less EGR and better air/fuel distribution. These effects could conceivably be contributing to your misfire at idle.
So maybe I've merely 'masked' some other problem by changing my vacuum connection to the timed port, such as worn valves guides, sticky lifter, cracked valve seat etc?

It has been perplexing to say the least, as it has come and gone seemingly with random adjustments to different components. I was gutted that it was still there after fitting £400 worth of carb and manifold. :cry:
I think I'll stick with this setup for now, unless the misfire comes back, as it is no great drama, just a frustrating exercise trying to get rid of it the annoying thing :evil: