I would actually advise that you get your timing ironed out BEFORE trying to set idle speed. I recently changed carbs and recurved my distributor and found that my timing was WAY off. This greatly complicated trying to set the carb right. For whatever reason the factory carb would tolerate it, but always had this annoying stumble off idle and seemed down on power. I wanted to swap it for something more readily tuneable so I went with an Edlebrock 500. In the process I found that the timing that had been set was about 50 degrees off. It never pinged. I suppose the compression is just low enough that on 93 octane it tolerated it.
So first, use a piston stop to determine actual TDC. Set the distributor at 0-10 degrees ATDC (its going to change when it warms up, so this will get you close, but once its running and up to temp you can set actual base timing). You need to know what the compression of the engine is to determine how much timing you want at full advance. If you pull the rotor off the shaft and remove the breaker plate you will see the mechanical advance mechanism. This will have a tab and two cutouts marked with something like 10 and 15 or 13 and 18. The cutout with the tab in it is the one its running off, so if it reads 10 you are getting 20 degrees of mechanical advance, etc. The lower the compression the more timing it will need, also the less efficient the heads are the more it will need. I run 38 degrees total. I set base at 12 degrees BTDC and my mechanical is on the 13 cutout. I put light springs in it so all the advance is in before 3,000 RPM. It made a HUGE difference in how much power the car had.
You can flip the plate with the cutouts over if you need the higher or lower advance setting, but it requires removing and disassembling the distributor. Too much base timing can result in detonation, but if the compression is low enough it probably won't matter anyway. Keep in mind that factory compression ratios are a bit optimistic. If the book says 8.5:1 its probably more like 8.3:1, etc. There was a far wider variance with things like deck height and chamber volume back then than there is today. HG thickness does make a difference too, so if you've gone thinner its increased, thicker decreased, etc.
Once you get that at least mostly sorted out you can set your idle and tune the carb. Trying to do two things at once means both suffer and you will drive yourself nuts like that.
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MS wrote:
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