Backfire through the carburetor....help!
Thread Starter
Racer
Joined: Feb 2012
Posts: 462
Likes: 0
From: Virginia
Backfire through the carburetor....help!
Hi everyone, Im new to this forum and Im hoping to get some enlightenment from you guys. 
My 1973 Corvette has a Chevy 402 BBC(not original) with about 140K miles...and lately it started back firing through the Carburetor when I first start the engine....I have two mechanics and both have done a compression test. One says it's a burnt valve#1 and the other says it has bad rings because when he put oil into the spark plugs sockets the pressure changed and all valves had pressure....
....It's hard enough finding old school mechanics who know what they're doing..never the less working on C3 Corvettes.
Any suggestions?
My 1973 Corvette has a Chevy 402 BBC(not original) with about 140K miles...and lately it started back firing through the Carburetor when I first start the engine....I have two mechanics and both have done a compression test. One says it's a burnt valve#1 and the other says it has bad rings because when he put oil into the spark plugs sockets the pressure changed and all valves had pressure....
....It's hard enough finding old school mechanics who know what they're doing..never the less working on C3 Corvettes.
Any suggestions?
Burning Brakes
Joined: Sep 2012
Posts: 818
Likes: 0
From: coon rapids mn
what are the numbers from the compression check ?do a leak down test.if you hear air leaking from the carb ,its a bad intake valve.if you hear air from the oil filler hole in the valve cover ,its bad rings.if you hear air from the exhaust pipe ,its a bad exhaust valve.whats your timing at ?check for any bad wires or a bad distributor gear.check and test your power valve if its a holley carb.
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
If it does it on starting then make sure all your vacuum hoses are connected. 150K on a Gen1 motor is quite a bit, it is probably ready for an overhaul regardless, the motors didn't last that long that many years ago. 
Racer
Joined: Jan 2007
Posts: 427
Likes: 1
I am just throwing it out there... Timing chain jumped?
The cause of the back fire maybe the carb sucking air or maybe too lean on a plugged shooter?
I support that Holley powervalve. It maybe blown now with the recent back fire.
The cause of the back fire maybe the carb sucking air or maybe too lean on a plugged shooter?
I support that Holley powervalve. It maybe blown now with the recent back fire.
