Dual Carb Vacuum Hoses

by Richard Atwell
(c) Copyright 2005-2011

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72-74 carbureted models have a complicated system or vacuum hoses and hard lines. This is how the 1972 models hook up. The 73-74 models distinguish themselves with the addition of a smog pump, EGR system and paper air cleaner.


Vacuum Hose Layout:

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The above photo shows how the distributor vacuum hoses connect to the left carburetor but on some models, there is a vacuum advance cutoff that goes between the distributor advance and the carb so I've bypassed the cutoff for the sake of illustration.

hoses cutoff
On left carb (34-PDSIT-2), Left side nipple is advance, right side retard. The cutoff is activated by a switch on the transmission. Bentley says it exists on all dual carb models except 1974 with manual transmission.
distributor airhorn
Distributor. Two hoses connect to a temperature valve on the right air horn...
controlbox righcarb
The red hose goes on the right nipple and goes to the control box on the air cleaner. The green hose goes to the rubber tee on the left carb for the brake booster line.
airhorn oilbreather
There is a pipe that connects the left air horn to the left carb's central idling air intake. The oil breather hose connects to the back of the air cleaner.
aircleaner
The oil bath air cleaner.

Charcoal Canister:

engine Before the introduction of the smog pump in 73, the 72-74 dual carb engine layout was quite clean if not cluttered by various layers of vacuum hoses. If you look closely you'll see there is no engine hatch (72 was a cross over model year).
canister Before the charcoal canister was mounted on the firewall and later behind the battery (1978) it sat in front of the booster fan. Air came from the fan shroud instead of the engine tin through the same hole used to adjust the timing in 411s and 914s on models that used air conditioning. Non a/c models had a nipple on the left side of the fan shroud using another 90 degree rubber boot.
canister These elbows are usually cracked and over time need to be replaced. The hard lines of the vapor recovery system are virtually the same on 72-79 models.
canister Fuel vapors that are filtered by the charcoal canister are blown into the air filter. That is an oil bath air cleaner in the background.

References:

History:

4/26/05 - created
09/05/11 - Fixed broken photos, added translate button, updated footer