According to my Mallory Instructions, the selection of springs can determine whether you want a straight line advance or a curved advance. I don't have a spring kit, but it appears that some of the heavy springs install "loose", so they dont' start to affect timing until later rpms, hence the bump. Here's the link that explains it:
http://www.malloryperformance.com/pdf/29015.pdf
Piston-Stop Tool. I made my own. Knocked out the center of a spark plug and threaded the inside for a bolt. Using the tool, you advance from either side until it stops and read your balancer. 1/2 way between is top dead center. I don't like using the tool as the engine has some resistance to turning by hand (even with all the plugs out, there's some), so I don't want to have the piston hit the tool too hard. So, here's another way. Rotate engine to 10 BTDC and insert a long rod down the plug hole until it lodges up against the top of the piston and the far cylindeer way. Make a mark on the rod and a corresponding mark where it rests (you have to hold it) against the valve cover. Remove rod. Rotate engine to 10 ATDC (preferably form the other direction, but it's not that critical). The marks shold line up perfectly if your Balancer is correct. I use +/- 10 as a balancer usually shows both.
So....most people have timing from about 14 to 20 intial and never more than 38 max. I could live with the 20 initial as the engine heat problem is more or less gone by that point. I still have the bog though, and I guess I could tune that out. It's either getting too much or too little pump shot, starts to recover and then the secondary's open and then it's off. With further advanced timing, all those problems dissapear. However, with these timing settings, the enigne seems to be firing with late timing...engine sort of pounds. When it's too far advanced, it's different...like a reluctance to keep incresing rev's...sort of as described earlier ...like a rev limiter is at work.
Waht I expect at correct timing is a freee revving, light sounding enigne. It id that once, but as the balancer had slipped, I don't have much of an idea where that timing was....but it looks like 36 intial....yikes!
Curretnly, at 28 intial and 38 max, my new plugs are slowly turing gray (and I suspect, eventually will turn tan). When I had detonation problems before, I had another warning sign I should have paid more attention too....sparkling white porcelin plugs....gleaming...more white than new "out-of-the-box" plugs.
To get rid of the bog.....hmmmm. I am already using the light springs in my vacuum secondaries. I have the spring kit, and there is a set of lighter ones, but I tried installing one once and it wasn't long enough to even stay in position under the diapraghm. I also have a couple of pump cam kits, but it's set pretty light now. Maybe a couple more choices to limit the pump shot.
Just seems odd as it worked well before. Darned engine. I am sure I can get it to run great, but the timing numbers defy all data and experience. I kind of wonder if I seem to need such high timing as I am using a single plane 2x4 manifold with poor port matching to the heads. Poor mixture, so more advance needed.......
Anyway, thanks for all the replies. If anyone can think of anything else to shed light on the matter, I'd appreciate it.
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