Post
by JagWaugh » Sat Jul 02, 2016 8:06 am
Andrew,
The cap and rotor don't make a difference to the timing. They may make a difference to the HT connectivity, but the firing angle is entirely determined by the low tension side.
Good idea with the angle disc. It does give you the max mechanical advance, and with a mightyvac you could also determine vacuum advance or retard.
The best thing to do is to get access to a distributor tester, as this gives you the full story. Last summer I was working on a TR3, the rotor seemed to be moving and returning under the action of the mech advance judging by the wiggle test, and we walked the stages dynamically with a timing light, but the car still ran like crap.
By coincidence we happend to be at another nearby shop and the conversation turned to distributors and testers. They had one, but it was broken. I offered to have a look at ît. A couple of hours and a 1n4004 diode later I put the TR3 Dizzy in and tested it: It was all over the place! My first reaction was that I had missed a fault in the tester, so we put a series of different spare distributors on the test machine. Some were bang on, a few weren't. Then I put a new 123 on the tester: it was bang on, so the tester was pronounced accurate. They now have a functioning tester, and we have free access to it (they're only 5 min around the corner).
Keep an eye out for a used distributor tester, they really are worth it. Once you've got the distributor out of the car and found the data indicating advance, rpm, and vacuum it takes all of 5 minutes to adjust and determine exactly what condition the distributor is in.
