Quote:
Originally Posted by many birds
How do you figure out where 10 degrees is?
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Depends on the distributor. Some breaker plates require a little more movement than others.
I weld the slot and start with about .125" of movement and increase from there as necessary. Some distributors require up to about .200" of movement. Shooting for 10-12 degrees of total timing is all you need from it.
The adjustables work like this. Tighten the spring it limits it's travel at the same time. So you can limit them to 10 degrees by tightening the screw but then they don't even start to work until they get hit with about 12-15 inches of vacuum and they aren't all done till 20 inches of vacuum or more, so that's not going to do it.
If you loosen the screw they'll work with about 5-7 inches of vacuum but then they travel up to 20 degrees of timing, and that's too much, so that doesn't work either.
So, I set them for the light vacuum setting where they start to work around 5 inches and they are all in by 8 inches, then I just weld the slot and limit the movement. So you get the best of both worlds. Works excellent in engines that have a lot of camshaft in them, and even mild engines, and also works well when you're a mile up in elevation and the engine isn't making as much vacuum.
Here's one I just set up for an engine I just built. This distributor was originally set up by someone on the forum, but they used plastic bushings to limit everything. When I took it apart the plastic bushings were hardened from heat and split, and falling out. So I weld them here as a more permanent measure.
This particular unit needed about .200" of travel on the vacuum advance which gave me 11 degrees at the crank.
I also set up the distributor advance the same way, welding the slot until I have about 10 degrees, which is 20 at the crank.