77 454 Backfire & tick

I am working on a 77 Custom Deluxe 30 w/ HEI ignition. It has a backfire through the carb. Happens when I crack the throttle, and is worse when the truck is on the road. Does not like over about 1600 RPM. Replaced the fuel filter w/o a difference. Put a timing light to it and found the timing mark to be "jumping around" at idle. I have checked the RV forumns and the thought is to replace spark plug wires, next cap, next rotor. Also, possibly replace timing set. Any thoughts???? Anyone know what initial timing is for this engine???

Also, engine has tick that seems to come from right side. Put a screwdriver to engine and found the noise more pronounced at where #4 and #6 intake meets head. What's the story with a flapper valve possibly creating this noise?? Man, I hate to think I have VALVE trouble. If so, what is the best way to isolate it.

Sorry a truck dude is on this forumn. But, I have run out of ideas on where to look. Thanks in advance for your help.

Check the advance weights, sounds like they are advancing too early.

The symptons you describe sound like you have a weak or broken valve spring (on the stock double wound springs, the inner dampner will often hold the valve closed enough to still give a decent idle but will not hold at any type of RPM).

I would pull the valve cover and check the valve train. The good new is the spring can be changed in vehicle without pulling the head.

I once had exactly what you mentioned going on in a 454 powered jet boat. It ran great until I brought up the rpms a bit above idle or placed the engine under load then it would pop through the carb. A number of people told me to look for a flat lobe on the cam but I just couldn't beleive it since it ran so well at low rpms. I fiddled with the timing and carb and gave up and pulled the valve cover.
It took me two seconds to see while turning over the engine with the starter to see that the No.8 exhaust wasn't opening as far as the others. Pulled it apart and sure enough, a flattened lobe.
Since then I've found others with the same problem and all have discribed what you are dealing with.

Just a thought........

I have had this problem on 2 of my chevy motors.
Both with diffrent solutions the first was a wore out spring causing the valve to float at any rpm above idle

The other was on a big block and yes it had worn cam lobe the ticking was from the push rod droping to far and ticking when i hit the rocker at higher rpms and causing a top side back fire

First i would check that side valve springs and hope that is what it is

good luck with the problem