POW!...goes the pop-off

[JP911]

As the subject line clearly states: I've had a backfire. Fortunately, the pop-off appears to have saved the airbox. Unfortunately the pop-off blew clean out of the hole! I actually ducked when I heard the backfire, thought somebody was shooting at me. I suppose it's just reflexes from my days in Philly

So what's next? Should I clean all the old epoxy of the pop-off and reinstall? Buy a new pop-off? The hinge seems fine and the spring is intact. Not sure what to do. Any advice? Also, the car has never backfired before, what could be the cause? Many questions...

Oh, and the beauty of all of this is that I was about to take it to get aligned and corner balanced so that I could finally drive it after having completed the suspension in early January. I tried to take it in January, but I had a fueling problem. Then I decided it would be a great time to replace the dash pad and rebuild the transmission. I think I'm cursed.

[Bill Verburg]

Congratulations, you just saved yourself ~$1000. I don't understand how the whole unit could have blown out. Did it take part of the air box with it? If the epoxy just let go sand all of the remains off and reinstall.

[JP911]

There is a clean hole where the pop-off used to be. There isn't even any epoxy residue on the airbox itself, it's all stuck to the sides of the pop-off. As I think about it, I seem to remember that the valve was installed backward (installed by PO) so that the hinge was facing the front of the car rather than the back. So the valve probably couldn't open all the way and it just let go to relieve the rest of the pressure?

[vash]

haha, welcome to my club! i managed to clean the epoxy with a tiny pair of angle needle nose pliers. watch out, that dried up glue is sharp! i cut the crap outta my hand when i was popping the old glue off the box, so gloves would be my next suggestion. most of the glue stayed on the airbox huh? well if that happens to me again, i think i may leave the old glue on the airbox. it forms sorta a chairlike seal right? i think a tiny bit of new epoxy on the valve will stick it there good. just rough up the valve with some sandpaper. if you decide to break the glue off, be prepared to use needlenose pliers to fish the pieces out of the box.

when did it backfire? from acceleration, decel, just driving along? that was the incident that made me take my car to a mechanic to have the mixture checked, i was way lean, and that is why i blew!

[autobonrun]

I understand that the most common time for a backfire like you experienced is during seasonal changes. I know mine let go in November during a cold snap when I lived in Houston. This happened in 1984 and I did not have a pop off valve. The airbox was destroyed. I've had maybe two more backfires since then, also when the weather turned from warm to cold. The popoff valve saved me.

I'd check the mechanism and the sealing surface. If it is still good, I'd just reinstall it in the correct direction and with some stronger epoxy.

[JP911]

The epoxy is actually stuck to the valve and not the airbox. The airbox is actually pretty much free of debris. The car was sitting in my garage at the time, which is a good thing. I was starting it up so that I could drive it to the P-car shop to finally get it aligned and corner balanced. It just doesn't seem to want to get back on the road.

[vash]

betcha your car is running lean. you described my starting procedure a few month ago. it usually started with a prayer. wonder what your plugs look like?

[brawlins]

I blew off my popoff valve twice. Not the lid. The whole thing.

I probably should have taken "unfixed"'s advice and just roughed up both surfaces with sandpaper and re-epoxyed it.
I had my popoff valve plastic-welded to the airbox. I guarantee it ain't comin' off again.
By the way, we both saved money by avoiding a cracked airbox.

- Bill

[on-ramp]

shouldn't the valve just open instead of the whole thing flying off like that?

i thought that was the whole point of installing a "pop-off valve".

unless it wasn't glued properly to begin with