454 backfire (pops) in exhaust

grewvin1

Petty Officer 2nd Class
Joined
Apr 2, 2012
Messages
189
1987 454 new points set dwell, timing,cap, rotor and plugs. Tried new coil. Get it up to 2200rpm under load and pops in exhaust no power. Timing light can see variance in light will float from 8 to 10 degrees.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
48,175
its not the coil - it almost is never the coil

poping in the exhaust is most likely really late timing.

poping in the intake is advanced timing or running lean

are you sure you set the timing to 8 degrees BTDC and not 8 ATDC?

also, you may need to verify the outer ring of the damper hasnt moved. pick up a cylinder stop tool. rotate engine manual until #1 cylinder stops against tool and mark damper at 0 degree timing mark. rotate engine backwards until #1 cylinder stops again and mark the damper at 0 degree timing mark. directly between these two marks is TDC. if your balancer has not moved, this middle mark will be on the scribed line. if it has moved, buy a new damper.
 

grewvin1

Petty Officer 2nd Class
Joined
Apr 2, 2012
Messages
189
Yes sure timing is 8deg. BTDC but light will fluctuate between 8 & 10 in a constant rate like a dead miss. Wondering if sticky valve or such?
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
41,162
Double check your firing order 1,8,4,3,6,5,7,2 and if correct, do a compression test
 

harleyman1975

Ensign
Joined
May 12, 2003
Messages
959
Agree check compression My initial thought is burned exhaust valve. or possible blown head gasket between cylinders cross firing.
 
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