1970 440-6 timing

a real stupid question. Prior to the engine quiting on me yesterday becuase I spun a bearing I finally got the engine to run perfect after two months of trying. Here is the question, when I use a timing light and set the timing a 10* BTDC the engine will not stay running and when I finally said screw it and set the timing by ear which turned out to be 25* BTDC it ran perfect. Whats the deal? Is there anything wrong with setting the timing this way? As for previous messages on the engine the builder is going to fix it for me. Thanks for all the responses.

WOW, sorry to hear that but at least the builder is going to do the right thing for you...I'm not sure on your actual combo but run it where it likes to run...Just make sure your distributor mechanical advance is limited to the 34-36 degrees all in by 2500-3000 RPM{checked with the vac. advance unhooked}...And the idle RPM was not high enough to start the advance curve in the distributor giving a false reading...

How did you set it by ear?
-The best or highest idle?
-The most adv without pinging under load?

Most, if not all, motors will like a lot of advance at idle. Bad thing is it ends up with too much total when you drive it.
Setting it by ear usually means to adv the dist till it pings under hard accel, then back it off a bit.

Hope your motor repair will be an easy fix.