That makes sense, the heavier the spring the more centrifugal force it's going to take to expand.
Well if you bought the kit from HO Racing it might be meant for a race engine with very high cylinder pressures. One may not want to get full mechanical until higher rpm unlike a street/highway car that would want it all in in the early 3000 range.
I have mine set at 28 total, I had to make a lot of adjustments to get 28 total at 3200 and still have the mechanical start to come in at higher than idle rpm and have a good initial for starting and keeping a smooth, cool idle. Lot of trial and error involved.
Most engines will run great with a close to stock timing and advance, but once it's modified it takes some screwing around to get optimum setting. Chassis dynos help for this but cost big $$$
You recurving due to problems with detonation or power?
