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Re: ZS to HIF

To: "MG list" <>, "Barney Gaylord"
Subject: Re: ZS to HIF
From: "MonteMorris" <>
Date: Wed, 15 Oct 2003 22:56:11 -0500
Thanks Barney,
Duh, after you pointed it out I see that it mentions the socket head cap
screws (I suppose these are not really screws if they screw into the
bolt-threaded holes on the carbs?) on the website address you posted below).
A few more questions:-).
1. Where can I find the vacuum tap point for the dizzy number that I have? I
found the dizzy timing on Paul's site.
2. I have the same aftermarket air cleaners that are shown on the address
that you pasted in below. They came with a metal backing plate to mount to
the carbs. From the picture, I'm assuming that this plate is not used if I
bore out and mount the old air cleaner back plates as shown? Do I just
stretch the new oval air filters around the old back plate?
Thanks again,

----- Original Message ----- 
From: "Barney Gaylord" <>
To: "MonteMorris" <>; "MG list" <>
Sent: Wednesday, October 15, 2003 12:04 AM
Subject: Re: ZS to HIF

> At 10:58 PM 10/14/03 -0500, MonteMorris wrote:
> >....
> >(HIF's and all related hardware off  a 74 parts car. They are going onto
> >desmogged 79B)
> >
> >1. the 74's instruction plate by the radiator says: time to 11 degrees
> >BTDC at 1500 RPM and gap plugs at .025. The 79 is timed about 18-20
> >degrees BTDC, .035 plug gaps, and has a points dizzy in it. What settings
> >should I try now and should I use the dizzy out of the parts car, or keep
> >the one that's in the 79 (45D, I believe).
> Early cars took distributor vacuum from the rear carb venturi, so vacuum
> came up suddenly when throttle was opened.  Later cars took distributor
> vacuum from the intake manifold, where vacuum is high at idle and drops
> suddenly when throttle is opened.  The distributor model has to match the
> vacuum tap point.  If you get it wrong you end up with a nasty case of
> vacuum retard which really screws up spark timing and engine torque.
> When you get the vacuum tap point and distributor matched, then use the
> timing spec that goes with the model year for the distributor.
> >2. I rerouted the heater hose (with metal tube) downward between the
> >manifold and the heat shield. Will this cause any problems, or should I
> >put it back up by the valve cover?
> Metal pipe along side of valve cover and dropping in front of exhaust
> manifold to commect to "T" at water pump inlet is not a problem, as long
> the water pipe is not touching the exhaust manifold.  That's how it was
> done on MGA and early MGB, at least through 1967 models, maybe through
> 1969.  Moved up top by 1970, presumably to clear space for some emissions
> >3. On the Chicagoland MG site,  I read to use the old alloy back plates
> >off the 74's air cleaners to put inside the oval foam air cleaners
> >(#223-220, pp. 7) so you can use the Unisyn easily without removing the
> >air cleaners.
> Actually the alloy plates are used to improve air flow, similar to stub
> pipes.  The bit about using the Uniflow was to counterbore the bolt holes
> in the alloy plates to make the screw heads flush.
> >I can see you must bore out the mounting holes on the back plate so the
> >bolt heads will be flush, but what type of mounting bolt (head) would you
> Socket head cap screws.  That info is smack in the middle of the page
> right below the picture of the modified parts.
> Barney Gaylord
> 1958 MGA with an attitude (and a quick camera)

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