[Chevelle 1969]

Started my chevelle today it´s been stored for the winter. If I adjust the timing were it should be 35 degree total and 24 initial it backfires in driver side exhaust. If adjust timing to 60 degree total it stops backfiring. What can cause this? 100% sure balancer hasn´t spun, since I timing was fine when stored and distributor pointed at same direction.

Only mods is new headers.

Have a spare carb that I tried just to verify it´s not the carb. Steady vacum and shows same value as it uses

Engine is a 454 with 10:1 in comp, Brodix Race Rite rec heads, hyd roller 242 248 .600 .610 in lift, HEI with MSD al 6, Pro System 1000 hp carb.

 

[dreis454]

Were the spark plug wires off when the headers were installed?
sounds like some crossed wires.
check the firing order.

 

[Chevelle 1969]

Were the spark plug wires off when the headers were installed?
sounds like some crossed wires.
check the firing order.

Yes they were off when I made the change, almost sure they are were they supposed to be, will check again to be 100% sure.


Can I make a piston stop from an old sparkplug and rotate the engine to check so the balancer hasn´t spun cause thats the only thing that makes sense now? What else shall I verify?

 

[Cameano]

You might be able to see the piston at tdc with the plug out to check the balancer. It should be close enough that you'd notice the 35° discrepancy.

 

[Mike]

Can I make a piston stop from an old sparkplug and rotate the engine to check so the balancer hasn´t spun cause thats the only thing that makes sense now? What else shall I verify?

BBC's arn't like SBC's ,the crank key lines up with the TDC mark so it's easy to see if it's moved.

Forgot to add that an exhaust leak will cause a backfire too ,so check your driver side header for loose/bent/etc flange connections.