Engine backfire
Thread Starter
Burning Brakes
Joined: Jul 2008
Posts: 914
Likes: 10
From: Brooklet Ga.
Engine backfire
I have built many many engines and have never had this problem. I built a 383 for my 73. I built it up with a Comp Cams 270 magnum cam with roller rockers, an Edelbrock Performer intake and 600 Holly and Pertronix ignition module in place of points. The car has a 4 speed transmission. The engine starts and idles just fine holds good oil pressure and dosent run hot. When I take it out and get down on it the engine will backfire the first few seconds and then seem like it gets it`s breath and takes off like it should. Going down the road I can feel the engine missing really slightly every now and then and it will softly backfire and it happens on both sides at random times. I have checked everything from timing to rocker arm settings, carb adjustments and everything and I can`t find it Does anyone have any ideas?
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
I have built many many engines and have never had this problem. I built a 383 for my 73. I built it up with a Comp Cams 270 magnum cam with roller rockers, an Edelbrock Performer intake and 600 Holly and Pertronix ignition module in place of points. The car has a 4 speed transmission. The engine starts and idles just fine holds good oil pressure and dosent run hot. When I take it out and get down on it the engine will backfire the first few seconds and then seem like it gets it`s breath and takes off like it should. Going down the road I can feel the engine missing really slightly every now and then and it will softly backfire and it happens on both sides at random times. I have checked everything from timing to rocker arm settings, carb adjustments and everything and I can`t find it Does anyone have any ideas?
Any time an engine backfires it means the spark is occurring too early or an intake valve isn't seating well enough to seal combustion pressure or an exhaust valve isn't opening (such as when a push rod breaks). Its very possible you have an egg-shaped intake valve guide that is allowing the valve to seat sometimes and not seat sometimes and is the cause of the intermittent backfiring. Its also possible you have a broken intake valve spring that is barely enough to hold the valve against the seat. I suggest you take a compression test and suspect any cylinder that reads exceptionally low.
Thread Starter
Burning Brakes
Joined: Jul 2008
Posts: 914
Likes: 10
From: Brooklet Ga.
Any time an engine backfires it means the spark is occurring too early or an intake valve isn't seating well enough to seal combustion pressure or an exhaust valve isn't opening (such as when a push rod breaks). Its very possible you have an egg-shaped intake valve guide that is allowing the valve to seat sometimes and not seat sometimes and is the cause of the intermittent backfiring. Its also possible you have a broken intake valve spring that is barely enough to hold the valve against the seat. I suggest you take a compression test and suspect any cylinder that reads exceptionally low.
