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Carb or Timing?
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alastairq



Joined: 14 Oct 2016
Posts: 1950
Location: East Yorkshire

PostPosted: Mon Mar 29, 2021 9:50 am    Post subject: Reply with quote

Thanks for that Dave, I'd mislaid my vacuum charts!!

I set up my ol' Mustang 6 pot using a vacuum gauge. Very helpful, took away loads of guesswork. [I had ''inherited'' an engine a previous [US?] owner had 'repaired' using mismatched carb and distributor. This is a common fault on these Ford 6 pots[there were/are a lot of them about]....done by folk who don't fully understand what, & how, Ford did these things. Bought a new distributor [electronic] which was cheaper than buying the proper carb, but all needed setting up. [still have to 'adjust' the vacuum pod, using an Allen key]....This involved painting Tippex onto the bottom pulley where the timing marks were, having calculated how far round 30 degrees [for full advance] should be...etc. The vacuum gauge gave me timing at tickover, mixtures, etc....Anyway, it runs like a good 'un now [with 50 thou plug gaps too]....}

What I find odd is despite vacuum gauge tuning being standard procedure in the USA, it doesn't seem to have truly caught on in this country?

I would like to add, the vacuum measured should be manifold vacuum, not ported vacuum.

I have a problem with the Ford sidevalve 100E motor in my Dellow..it has 2 SUs which have several vacuum take offs....none of which are truly manifold vacuum take offs. Legacy of the days when they were subject to all sorts of emissions issues. The Aquaplane inlet manifold has one tiny bore plug on one side [not ideally placed, better in the middle?] so I'm having to resort to buying [???? On my pension??]...a pair of carb manifold insulators that have tees bored into them for vacuum takeoffs...[Or, make my own with what I've got?}

Of course, I'd love to be able to seal off the throttle spindles...not badly worn, but still suck air a bit when opened...
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.
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Rootes75



Joined: 30 Apr 2013
Posts: 3785
Location: The Somerset Levels

PostPosted: Mon Mar 29, 2021 10:51 am    Post subject: Reply with quote

So whereabouts am I looking to take the reading for a vacuum test on the manifold area? Is it any port as long as its below the carb?

We did notice we have a couple of small pin holes in the exhaust downpipe only around an inch below the manifold, we will seal them up before we try it again.
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Various Rootes Vehicles.
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alastairq



Joined: 14 Oct 2016
Posts: 1950
Location: East Yorkshire

PostPosted: Mon Mar 29, 2021 11:10 am    Post subject: Reply with quote

Yes!

Manifold vacuum is taken off at any spot under the carb throttle butterfly.

I.e., between the carb flange , and the engine.

{Ported vacuum is taken from the butterfly area. On SU's, the butterfly covers the ported vacuum hole when closed. As soon as the butterfly opens, the ported vacuum hole is uncovered. This was done to help emissions at tickover, when piped to the distributor. Another source of vacuum signal is the carb venturi .

The problem with venturi vacuum is the signal drops to zero at times.}
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.
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