Whats the inside of the cap look like? Is there any carbon tracing inside? Carbon tracing will look like someone took a lead pencil to the cap.

Whats the rotor look like? Is the tip eaten away at all? What about the posts on the inside of the cap? Do they have any grooves in them? Is the spring on the rotor making good contact with the center post on the cap?

It sounds to me like spark is either being cross fired from carbon tracking, or it's not jumping the gap at all due to weak spark.

So, it could be...

Weak Coil
6AL box is firing
Carbon inside the cap
Rotor to cap connection isn't sufficient.

Just speculation though.

I have mine locked out and I never have to touch the timing once the distributor is in, although I do check it with a light. I put the balancer at exactly 38 deg btdc and put the distributor in with the rotor pointed exactly at the #! plug post...If I need to I turn the oil pump with a screwdriver. It has always been on the money when I start it and put a light on it. This only works with the advance locked out.

i think your timings off from what you think it is or theres another issue

I'd re-gap the plugs to no wider than .032 and try again.
JMO>Cp

I THOUGHT OF THAT,BUT MSD SAID 45 TO 50,WHAT WOULD BE THE REASON OF A SMALLER GAP?

I HAVE NEVER THOUGHT OF CHECKING THE CAP AND ROTOR.IT HAS BEEN ON THERE FOR 2 YEARS NOW.

1 PIECE ATI BALANCER

A few more ideas if the cap & rotor check out: rotor phasing way off or if you have a bronze dist gear, it may be worn out.........

High cylinder pressure can "blow out" the spark if the gap is too large....maybe a poor way of wording it.

GEAR IS NEW, BUT I CHECKED IT WHEN I HAD THE DIST. OUT AND IT LOOKED GOOD.IM GOING TO RACE IT TONIGHT AFTER I INSTALL NEW PLUGS AND CAP&ROTOR.