May wanna pull the dist cap and look for carbon tracking. I've seen that cause some really odd symptoms.

Exaust starts to open (adjust intake) Intake full open then almost closed (adjust exaust) I have found this works for me.

Tom,

Your valve adjustment is incorrect.

Bob

you were 180 out,my guess is their was unburned fuel left over that could have made the backfire..also on a side note i like to go a 1/2 turn after zero lash, reason when you go one full turn to cpmpress the plunger in the lifter and if that lifter were ever to malfunction it could expand .100th and the valve could kiss the piston..1/2 turn gives you extra clearance if that were to happen..

Those Morel's will rattle if there not a full turn down, believe me I know

#1 cylinder TDC compression (both valves closed) bring pointer + line on damper to 10BTDC. Get your rotor to point dead nuts at #1 inside cap. Make sure carb is full of fuel. Start key and braaaappp, it's started.

First put the bong down!! Then fix it!! Lol

I'm switching back to beer.

I recall using a timing light on #1 plug wire with ignition on to hone in on the distributor position to set up initial timing. Not sure if this will work with a Tbolt IV.

I went through and readjusted the valves using the procedure outlined by fbc25 - exh starts to open, adj intake, when intake is almost closed, adj exh. Started it again and it ran for a second then backfired hard thru the carb. Almost certain the power valve has to be toast after that one. Went through and double checked to make sure distributor is in the right position and not out of phase. It's right, and this time I set the mark on the balancer to the 10* adv mark on the tab, then made sure rotor is pointing to #1 as SB suggested. At this point I'm too tired to fool with it anymore and it's getting too late to fire up a big block with open headers and expect my neighbors to still like me tomorrow. Going to give it another shot tomorrow. If it's still backfiring I guess the next thing to do would be a leakdown test to make sure I didn't bend a valve, although I'm almost 100% certain that didn't happen. Pushrods were all fine and this thing just turned over too easily by hand to have any valve / piston interference.