General timing questions

[BNC04]

After several sessions of learning on my motor, I think I have things somewhat squared away and have been finally driving the bronco some over the last weeks, tweaking things as they crop up during some of my test runs.

I have something that may or may not be normal though and thought I'd post it up here for you pondering folks.

My timing changes after driving-

It is set at 12 degree base timing with ported and full vacuum blocked at the carb. Runs good, responsive, idles at 750 RPM with just a little lope to it (RV type cam)
After I drive it a bit, The idle will move and stay at 1050 RPM and the timing will move and stay at 30 degrees at idle. Still runs fine, idles strong, runs strong.

The plugs all have a light brown color to them, not sooty or oily.
Could the mechanical advance be sticking? I have unplugged and blocked the the vacuum advance at the carb and there is no change in the scenario.
Vacuum leak? I have sprayed cleaner all around no obvious change. I won't be home to tinker on it this week and thought if there was some words of wisdom out there I'd like to get a mental start on this.

Thanks
Brett

[BNC04]

Just did a quick check and there is about 1/4" vertical play in the shaft by lifting up on the rotor. No time to look deeper than that until next weekend.

Thanks for the suggestion.
Anybody else have things I could add t my list of items to check when I get back?

Brett

[MOLLEY]

what kinda dist are u running ? msd ? / if it has a brass gear / that gear could have a wear spot on it . like a step. . check oil dip stick and see if u have small brass flakes on it or pull dist and look at gear .. teeth will look like they are worn to sharp point . if so replace gear .i had this same trouble good luck
cheers Molley

[BNC04]

Thanks for the help guys. Popped a new dizzy in this morning and runs much better and timing stays where it is supposed to. There was quite a bit of slop in the old dist.

Brett