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1971 Spider (USA) 1750 Spica, 1974 Spider, 1976 Spider, 1981 Spider
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Discussion Starter · #1 ·
I have this engine from a 75 Spider and am baffled by this vacuum fitting off cylinder #1. Can someone tell me what it’s for?

Motor vehicle Automotive fuel system Automotive tire Gas Automotive exterior
 

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Likely for a vacuum advance on a distributor. I think there is a vacuum line to the oil vapour separator, it might come from there, the fifth line off the spica idle tower is for fuel vapour system.
 

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Spica cars didn't have vacuum advance but late two-sets-of-points cars had vacuum retard with a vacuum switch to change which points were in operation. I think this is that port. Goes to a vacuum switch on the inner fender then two wires to the distributor. Alfettas had it too, same engine was EPA-homologated for Spiders and Alfettas in spite of the installation detail differences.
Andrew
 

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1971 Spider (USA) 1750 Spica, 1974 Spider, 1976 Spider, 1981 Spider
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Discussion Starter · #4 ·
FWIW, it’s a Spica engine. Fifth line off the idle tower goes to the OVS. Engine came without a distributor, so no clue there. However… a BT 123 Ignition with vacuum port is going into this engine. Can this vacuum source be used for that?
 

· But Mad North-Northwest
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If it's vacuum from the #1 intake runner that should be fine for vacuum advance, the Alfetta engines pulled vacuum advance from the same place. That's where mine is hooked up in the GTV (it's got a later Alfetta engine).

On the Alfetta that port had a small orifice in the nipple to damp the intake pulses, not sure if yours has that. The 123 might work okay without that (it might have smoothing in the SW already?) but if not you might need to put a pulse damper in the line, something like this:


You can always try it without first and just watch the advance in the software, see if it's steady.
 

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1971 Spider (USA) 1750 Spica, 1974 Spider, 1976 Spider, 1981 Spider
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Discussion Starter · #6 ·
This might be my answer. I’m assuming that the fitting does the requisite damping for distributor vacuum.

 

· But Mad North-Northwest
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Easy enough to tell. Hook up a vacuum gauge, see what the needle does. If you don't have one most auto parts stores will loan you one for free, at least around here.
 

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1977 Spider 49-State
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It is a vacuum orifice with a check-valve for warm-air blend systems. This orifice would provide constant vacuum to a temp sensor located under the SPICA air box, which would then modulate vacuum (based on air box temp) to the air intake flap, which would blend warm air emitted from the exhaust manifold (piped via the famed hose over the cam cover).

With the engine off, the blend air system should be sealed from atmosphere, hence the check valve.
 

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Pre-1978 cars were slightly different. No T and no vacuum switch. They used a coolant temp switch located near the thermostat. Also, the dual points logic for those cars was opposite than later cars: 2nd set of points advanced timing during start-up and/or low coolant temps, then primary points took over. 2nd set of points were triggered by either start-up (via cold start solenoid) or the coolant temp switch. Both were wired to a relay on the inner fender in the engine bay that alternated between the primary and secondary set of points depending on operating conditions.
 

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1971 Spider (USA) 1750 Spica, 1974 Spider, 1976 Spider, 1981 Spider
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Discussion Starter · #11 ·
Jim's post #8 here pretty much describes what that vacuum port did
that line would have a "T" in it and in fact go off to two places:
Question: Where Does This Hose Go?

this plastic thing is the dual points gizmo he speaks of (iirc was fitted to 78 on, so not sure about it on a 75)
Have you a dual points Marelli dizzy?
View attachment 1760220
Actually, I do have that gizmo on the RF fender! The car is an 81 Spider that had the dual-points Marelli, but the engine in question is from a 75 Spider (?) and will be getting a BT 123 Ignition.
 

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Actually, I do have that gizmo on the RF fender! The car is an 81 Spider that had the dual-points Marelli, but the engine in question is from a 75 Spider (?) and will be getting a BT 123 Ignition.
The 80/81 originally had and awful marelli plex electronic distributor in them.
 
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