Andy Ramm wrote:
>
> I've heard it is not OK to use balanced manifold vacuum for
> distributor advance on an MGB. Is this true? If my carbs
> (HS6) do not have a provision for vacuum advance, but I can
> tap the manifold (has 2 outlets)for vacuum if need be. Is
> this OK? Will I be continuously over-advancing the timing
> at low RPM?
Andy:
The vacuum characteristics are very different. The MGB HS4
carbs were set up for ported vacuum, the HIF4 carbs for manifold. If
you can dig up a Dist. set up from a 72-74 MGB you will have a mech/vac
advance curve that will work with the manifold vacuum pickup.
Points type distributer Advance types
MGB Dist # Vac. # Vac. Adv. Type
18GF 40897 54411230 5.13.10 ported
65-67 41288 54411985 5.13.10
67 41290 54412170 5.11.7
68 41288 54411985 5.13.10
69 41264 54415625
70 41288 54411985 5.13.10
71 18GK 41339 54414868 7.13.5 manifold
72 18V 41370 54423989 7.13.3
73-74 41491 54425359 10.15.5
75 41599 54425516 10.15.5
Note the change in advance characteristics in 1971.
The later units come in at a higher vacuum and gives less advance.
10.15.5 = Movement starts at 10 ins of Mercury
Movement stops at 15 ins of Mercury
5 distributor degrees advance at maximum movement
Have fun Kelvin.
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