Setting Timing for 225 with HEI

I am setting up the new HEI distributor on my 67 CJ5 with the 225 and I can't rotate the distributor CCW enough to keep the timing from being retarded too much. I have ground on the manifold as much as I dare. How much can you grind it before getting into the water jacket? I had to use a buttonhead screw to replace the hex head that was in there originally. I tried shifting all the wires one notch but that makes it too advanced. I assume that being too far retarded is what is making it backfire out the exhaust as it is doing now? I have not adjusted the idle mixture yet as I was hoping to get the timing right before messing with the adjustment. To check the timing I disconnected the vacuum to the distributor and hooked the timing light to the number one ignition wire. wire. Am I doing something wrong and what can I do to make it right?

 

Since I'm so simple when it comes to distributors--do I pull it out, rotate the oil pump drive shaft a little counterclockwise and stab it, the distributor, back in a little more CCW than it was? Moving the distributor CCW advances the timing right? It runs right now but looking at the timing mark on the harmonic balancer it has to be at least 15* retarded.

How much can the head be carved, ground on, before you get in the water jacket?

Other than disconnecting the vacuum from the distributor is there anything else you do when timing using a strobe. Why does a motor backfire when the timing is retarded?

Thanks for the help.

 

OK, I got it fixed. I ground on the hold down on the dist cap enough to get the movement I needed. Thanks to the information gleaned from searching this forum. I wish I had searched first before burning up all those brain cells.

Man we're lucky Al Gore invented the internet.