Only runs 40 Degrees advanced

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Engine specifics were in earlier post but it is a 360 I rebuilt years ago it’s always been just a cruise in car so it doesn’t have that many miles. It has a whiplash Cam flat tappet MSD pro billet distributor at the moment with six AL box and matching coil has been running really good until this distributor got jammed. I was on the first day of the power tour I had ran almost 800 miles that day to get to the starting point I had just put in an a500 before I left that was really making the highway travel great

I am using a new timing light that says it can do both it seems accurate no dial back I set the motor to 15° by setting the balancer and then locking down the rotor right on the terminal then cranked it without fuel and watched it with the timing light and read 15° on the balancer but when I tried to start it. it would not hit At all until I turn distributor way up 35 -40° it starts and idles doesn’t overheat I can Revit up but you can tell it’s missing a little bit when you raise the idle up because it’s too advanced but for some reason that’s the only way it will run. if I try to lower the timing back down while it’s running it will stumble and die

I dig that car---
A little outa line but I gotta ask here , Whats the diff in an MSD light ?
I have had MSD`s on 5 diff. engines/ 4 diff. cars, and have never used any special timing light . All have run good to perfect . ?????
Selling hype by MSD ???