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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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I'm also a bit suspicious about your timing. Any more or less stock JH should run quite well with a static timing between 8^ BTDC and 12^ BTDC. They run less well (and much hotter) with timing in the 0^ BTDC - 5^ BTDC region, and quite poorly indeed when the timing is retarded beyond TDC. If you have the wrong crankshaft pulley for your engine's front cover, the TDC mark will end up 10^ off (don't recall which way). Unfortunately, determining actual TDC in comparison to the timing mark on the crank pulley can be a bit tedious, but may well be necessary if there's a real concern that you have the wrong part on the engine.
The vacuum retard mechanism was added to the JH distributor in an attempt to comply with emissions requirements at idle, but seems to have little actual effect. Yours probably has a ruptured diaphagm, a common failing after 30-odd years. Replacement vacuum capsules are unlikely to be available, repairs are all but impossible, and you can not safely use something from another British car unless it has very similar characteristics.
However, since the vacuum mechanism doesn't really do much, you can just ignore its failure and retain it only for the vernier timing adjust wheel. Alternately, you could cut off the big disk for the vacuum mechanism and keep the barrel part, securing the spring and threaded shaft with epoxy. Or you could throw it out and either fasten the two points plates together, or replace them with a single fixed one for a 23D series distributor (see Dave Bean's website. Usual disclaimers).
If you have to comply with emissions regulations that involve a visual check, leave the vacuum mechanism alone and in place, and plug the vacuum hose that runs to the distributor. Otherwise, you can remove the vacuum line entirely and cap off the port on the tee to which it was connected -- or simplify things even further, and run a line directly from the port on the intake manifold, to the vacuum switch inlet. If your engine's in even fair shape, and your carbs are fairly fresh, the car should still meet any state's emissions requirements.