>>the occasional backfiring through the carbs on initial
acceleration.<<
Scott,
Your own description above might be the answer to why you need slight vacuum
advance at acceleration and not at full speed wth your TR4..
There are very many different vacuum units out there so beware - not all the
same. the vacuum unit specs for TR4 were last upgraded around TR4 CT18000 and
I believe were good through to TR4A .
The important number stamping to look for on the vacuum unit are on the
narrowed front 'neck area' where the vacuum air tube screws or pushes onto
(have to look REAL close) Operating numbers should read as follows: 2-6-3.
There IS an eight digit 'part number' (something like 54413560 or 54413565)
that varies due to 'screw-on' connector or 'push-on' type and car make.
The vacuum 'operating numbers' are most important here.
These 2-6-3 numbers mean: A) it takes '2' H.G. of vacuum to start the
mechanism, B) the top range of useable suction is '6' H.G. and, C) the
maximum advance you'll recieve is '3' degrees.
- not much advance, but enough, at the right time.
If you have the good fortune of having the right unit 'number wise', even if
it leaks - might be easier to fix it or have it rebuilt - than to find the
correct one in working condition as they are quite rare unless you know of
someone with a stash of Lucas parts..
ps; the correct distributor body for later TR4 to TR4-A is stamped 40795
Carl
'63 TR4 since '74 - CT22326L
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