Now, as a preamble guys, I am away from my Bentley right now and am going by
memory.
The losanges form part of the emissions control system. The tear in the
anti-run on is the source of the original disconnection of the parts in your
case. Your car can run with everything disconnected.
Essentially, the emission controlled cars needed a later ignition timing to
burn cleaner at idle. This would cause engine overheating. Similarly, it
can help clean emissions during warm up. Thus, the factory provided a
vacuum retard circuit that was "disconnected" when the motor overheated to
get the best of both conditions. Enter the waxstat in the rad hose.
On TR6 cars, at least, said waxstat closed at a high temperature. This
reduced the vacuum to the vacuum retard module and thus effectively advanced
ignition timing (since engine vacuum is high at idle and light load).
ONE of the signals feeds the fuel shutoff via engine vacuum. However, it
cannot be cut off like the distributor retard unit or the car would stall!
And in fact, when the motor is shut off, vacuum ceases, the shut off valve
shuts off, and the car "stalls". (Remember that runon is caused not by
spark but by hot metal or carbon, so ignition shutdown is not the issue but
rather fuel supply). A punctured connection here would mean no fuel and a
stall. Such a vacuum leak, you've already seen by unplugging vacuum hoses,
would also cause a stall.
I still have no idea what the "fuel traps" really do, but I suspect they act
as a damper of sorts. Either way, if you can't blow through them they
can;t transmit vacuum either and are NFG.
One thing you can do for your vacuum retard is run a line directly from the
carb, bypassing all else. This was the early 70-71 TR6 solution, also
likely done on the spitfires of the time. You may also choose to disconnect
the retard function completely. Check with the comp. book but the TR6
timing (static) would be about 10-12 BTDC using this configuration. To get
the best from your car though, you would need to change the distributor
advance curve to that of a non-emissions car. But don;t be afraid to
experiment a bit - and remember... pinging is "bad".
Dave T
Winnipeg
-----Original Message-----
From: Kevin Besig <kbesig@borg.com>
To: spitfires@autox.team.net <spitfires@autox.team.net>
Date: February 16, 1999 6:48 PM
Subject: Re: vacuum amplifier?
>The Bently manual refers to these as "Fuel Traps", but I don't know what
>their purpose is either.
>
>Kevin Besig
>'75 Spit FM28619U
>
>
>John Weber wrote:
>>
>> Greetings all,
>>
>> I have a '75 spit, manufacture date of Jan1975 (according to the plate),
>> engine number 30xxxU.
>>
>> I seem to have very little (if any) vacuum at the distributor.
>> I know about the missing gulp (anti-runon) valve, it is missing, but the
>> lines are plugged. Take out the plugs and the engine stops. I assume
>> that plumbing is correct.
>>
>> The carb (CD150) is in multiple pieces awaiting kit from BPNW ($17.50),
>> and it looked fairly? good except for a tear in the anti-deceleration?
>> valving.
>>
>> Coming from the carb are two pipes that feed a lozenge shaped doohickey,
>> that subsequently feeds the distributor and (can't remember now)
>> something else.
>>
>> What *are* those doohickeys? Are they needed? I figure to take them
>> out unless some purpose in life can be proven and plumb straight to the
>> needed locations with 1/4 ID tubing for vacuum.
>>
>> Am I stupid? Any thoughts, recommendations, etc regarding my loss of
>> vacuum would be appreciated. When I drove it down here from the buy, it
>> had *NO* vaccum at the distributor, and I figure that needs to be
>> rectified.
>>
>> John
>> '75 Spitfire
>
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