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Re: ZS to HIF

To: "MonteMorris" <>, "MG list" <>
Subject: Re: ZS to HIF
From: Barney Gaylord <>
Date: Wed, 15 Oct 2003 00:04:14 -0500
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 a 
>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 as 
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 bits.

>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 use?

Socket head cap screws.  That info is smack in the middle of the page here:
right below the picture of the modified parts.

Barney Gaylord
1958 MGA with an attitude (and a quick camera)

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