Exhaust backfire (BIG BOOM)

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gumper

gumper

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Washed my car tonight so I could load it on the trailer and just head out to the races right after work. Went to start it after it was dry, and it kicked but wouldn't fire. So I pumped the throttle once, cranked it but nothing, pumped it, cranked, pumped once more and BOOM! Sounded like a cannon from a backfire in the exhaust. After I checked to make sure I didn't have an accidental movement that ruined my seat, I cranked it over again and it fired right up. I was concerned I had a major issue, but warmed it up just fine. Checked the timing and adjusted the idle a bit, and it seems OK when revving it up to moderate RPMs before I tucked the car in for the night. Do you think anything is damaged? Some fuel was probably hanging out in the exhaust, and then ignited with authority in my headers when it finally fired.
 
inertia said:
Check for "expanded" mufflers, if they are of any age. lol.
Click to expand...
Roger that! You got some raw gas in the exhaust and it lit off. I was thinking my '62's ignition switch was getting worn so I reached down to jiggle it to see while cruising at 35 mph; the engine cut out for a moment, and when it made contact again... KAPOW!
 

So you used to have 2.5 inch pipes and now you have 3 inch? :D
Sounds like the distributor might have gotten wet during the wash.
 
I had an intermittent ignition thing going on once about 30 years ago and it happened once at 55 on a busy interstate, blew one of the mufflers completely open when ignition came back about 1 second later.
Not the kind of thing that one forgets.
Scared my date for that night, and she was the nervous type already.
 
We used to drive around and scare old ladies on purpose. That was the early 70s. I don't do that anymore.I used to apply the brakes at 30ish and set the line loc. Then drive along with the front tires screaming, er squealing.
Now I just light up the tires, and people freak.Sheesh!People are so jumpy.....
 
It had 3" pipes with single chamber flowmasters. Now it's got stretch marks and no chambers :rofl: I kid, I kid. Everything is fine it looks like. I try to be very careful not to get my distributor wet while washing, and it's covered by my scoop tray. However, I did accidentally squirt my coil while rinsing the dust from the inner fenders. Figured it was dry when I went to move the car, but maybe some water was hanging around. Surprised my neighbors didn't call the cops thinking I shot someone.
 
Sounds like you may need to prime the engine more than one throttle pump. And make sure your choke is working. You likely had a very lean mix that stays lit so long, the exhaust valve opened and lit off the other unburned cylinders.
 
T56MaxTorq said:
Sounds like you may need to prime the engine more than one throttle pump. And make sure your choke is working. You likely had a very lean mix that stays lit so long, the exhaust valve opened and lit off the other unburned cylinders.
Click to expand...
It doesn't have a choke because race car. Usually two will fire it up. Four will wake the neighbors half a mile away.
 
On hot summer days, I have turned the key the first time in the morning, without setting the choke, and not only does the very first cylinder to get spark fire, but I hear one ping,
if I have 87 octane in there.
Still a good mixture in a cylinder, ready to fire. No detonation on highway, either, so it's not timing that's too advanced.
 
We used to turn the key off for a couple of seconds while the car was coasting, then turn it back on. BOOOOOM!
 
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