I knew a couple of people would verify/correct some of my original post.
1500 distributors do have vacuum retard. Disconnecting it allows more total
advance under high vacuum situations. Its original function was to retard
timing under low load thus reducing NOX emissions. Again, if possible toss
the 45DE4 distributor in the trash and replace with a 25DM. The advantages
of the 25DM is vacuum advance instead of retard, and a remote electronic
ignition amplifier which is more reliable than the opus unit on the 25DE4.
The 25DM was the distributor supplied under warrantee to replace faulty
25DE4's, and came standard on the late MGB's. They show up from time to
time on Ebay for about $100, not bad for a brand new distributor and
electronic ignition unit all in one.
Again, since it is possible to have many variations of carburetors,
distributors, advance curves, etc, a rough rule of thumb is to find a hill
on a hot day, and attempt to lug the engine. If it pings, retard timing
slightly and try again. If it doesn't, advance timing slightly and try
again. Once you are able to climb the hill under heavy load without pinging
the timing is probably maximized. Then if after a hot run, if the engine
runs on, retard the timing a little more. (This is assuming fuel mixture is
already correct).
David Riker
74 Midget
63 Falcon
70 Torino
http://home.pacbell.net/davriker
----- Original Message -----
From "Chris King" <cbking at mail.alum.rpi.edu>
To: <spridgets@autox.team.net>
Sent: Sunday, February 03, 2002 11:14 AM
Subject: Re: 1500 Weber and Timing
>
> In that case, you could plug the vacuum retard unit, since it is my
understanding (from a post on the UK MG BBS) that it only retards the timing
at high manifold vacuum, which is at idle and at high rpm coasting. Sound
right?
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