In my experience, going "in" from stock(to retard) is relatively linear(on a WORKING IP), going "out" is not - it hits a wall and won't advance any more.
Also, pretty sure the pin is acting on the cam 100% of the time - yes, it's only 'varying' during the cam-lift portion; before and after that, it's a "flat" profile" - but it still affects the timing the same way at any throttle position.
Also, something of note:
In my mind, if you are using a new IP, something that's actually to spec? Get it timed, go with the 'correct' adjustments and call it good.
Once you are using a worn out P.O.S pump that's been in use for years? Well, make it work, any way you can. That's when some of these other adjustments come into play:
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I just shoved an old, worn pump on my '93, so I could take my R&D pump for the 'big turbo' build. The used pump I *wanted* to use has issues(end play on the input shaft, missing bushing?), so instead I'm using a pump that came with a JY '93 motor. When I got it originally, it smoked above idle and was really retarded.
Currently, I've got it adjusted for DDing it, so it actually needed to work well.
The problem was, as I found out, the RPM-advance isn't working. At all. So, at idle it would be advanced, at 3K it would be smoking and missing.
In order to 'fix' that, I have:
1. IP gear is "skipped" 1 tooth forward(6-7 degrees of advance at nominal IP rotation).
2. IP is cocked about 1 degree retarded. (these two measures give me about 6 more degrees of advance at 3K, getting it into 'slightly retarded, but not smoking white')
3. Light load advance cam is pushed so far forward that it goes to 'full retard' at just off idle. (With the 'base timing' advanced so much, idle was now extremely advanced. "locking out" the added advance gets it back to a reasonable level).
This ended up producing a reasonable working timing set. Is it as good as a new IP? Heck no!
But I need the truck running good and don't have $500+ to spend on a new IP.
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That is the case where it pays to mess around, see how it feels and drives at various RPMs and adjust from there. When you need a new IP, but don't want to buy one. You pretty much have nothing to lose by messing with it.
Oh, and speaking of which... Everyone says that advanced timing will kill glow plugs almost instantly. Well, during my test drives with said worn IP, I had it *extremely* advanced down low at first. Clatter clatter clatter. And... all of my glow plugs are still fine. No short-cycling. 'Course, I do have ZD-9s.