You didn't say what compression you have, but with that cam you ought to be able to tolerate 15 at idle easily. Look at your Barry Grant Mighty Demon manual. I think my Speed Demon one says 16-18 for recommended timing, but I don't have it handy. Do you have the MSD 8572 Distributor? You want 36 degrees at 2500rpm with the vacuum advance plugged. If your distributor has 28 degrees of mechanical advance, when you set the timing for 36 at 2500rpm, you will have 8 at idle (36-28). If it's an MSD distributor, you can change the mechanical advance amount by using the different bushings that come with the distributor. For 18 degrees initial, use the 18 degree bushing, which is the physically largest one, and the lighter 2 blue springs, and set the timing at 36 degree at 2500. You'll have 18 degrees at idle and that spring set lets the mechanical advance be at it's max ("all in") at 2500rpm.
I started out with the 28 degree bushing, then dropped down to the 25 degree, now I'm on the 21 bushing so I'm at 15 initial. It starts fine and has great throttle response. I'm working my way up slowly. There's a "sticky" above the header when you're in the C-3 Forum section..."Setting your timing, by Lars" or not sure of the exact title. Read that.
Have you checked your timing at idle now? Once you get past idle does the engine run like it did before? If you're cruising at 2500 and punch it what happens?
