Popoff valve problems

[brawlins]

I probably should have asked this forum for their opinion before I got my wrench to do this, but...

My popoff valve blew out from it's hole in the airbox (I mean the whole valve, not just the lid) when I had a bad backfire (which is another issue).

I had the valve epoxyed in, so I'm not sure how it could have blown out.

Anyhow, I'm going to have it WELDED IN with a plastic weld. Am I nuts to do this?

Once I get the valve sealed in good, I hope to diagnose the backfire problem (unless it is all popoff valve-related).

- Bill

[74-911]

Mine did the same thing after about 15 years. I just removed the old epoxy from the popoff valve and the airbox, cleaned up then roughed up both surfaces and re-expoxied it.

From what I understand (and that's not much), it is virtually impossible to totally eliminate backfires on CIS engines.

[brawlins]

Do you see any downside to a plastic weld?

[brawlins]

Last time I'll ask the question, but perhaps no-one here has done it:

Has anyone done a plastic weld of their popoff valve instead of epoxy?
Any comments?

[stormcrow]

If you have a plastic welding unit, then go for it. Mine blew out once or twice within the last two years from backfire. Solved the backfire problem by enrichment of the mixture. Re-epoxied the collar back into the housing after cleaning with acetone. Havn't had a problem since.

You need to try and correct the backfiring problem - with that much pressure in the box, even with the pop-off valve, you could crack the box.

Steve

"A Porsche does more then just go fast in a straight line"

[vash]

i think plastic weld is overkill. plus what 74-911 said makes sense, when his blew off, he just fixed it with more epoxy. if you weld it, can you do the same repair if need be?

[brawlins]

Thanks for the advice, guys. I wonder how a backfire can blow off the whole valve instead of the valve opening like it's supposed to?

[makaio]

Originally posted by brawlins
Thanks for the advice, guys. I wonder how a backfire can blow off the whole valve instead of the valve opening like it's supposed to?

Well if your backfire was anything like the one I had in my SC, then it has a lot of force. It's really quite simple, if the force of the backfire can not escape through the pop-off valve fast enough, the force will overcome the next weakess link and go out that way. Hence blowing your pop-off valve out of it's epoxy. I would check your air box very carefully, becasue you could have a crack in it you don't know about, and it will be very hard to get it to run right like that.

[brawlins]

Thanks. I will post the results of what is found.

[Hladun]

Take out your AAV and you'll eliminate startup backfires.

[brawlins]

Here's what my wrench found out:
1) The backfiring and awful performance was caused by a corroded wire (malfunctioning) in the CIS system. It was replaced.
2) The blown pop-off valve was turned around backward (to give it more clearance from the air filter) and plastic-welded in.

She runs great!!!

By the way (see previous poster), what is an AAV? Sorry I do not know.

[cab83_750]

STAY with epoxy! I first pop-off valve disintegrated. I mean it broke apart. The toilet cover piece was in 3 pieces barely together. The epoxy was also barely there. Welding it might cause it tear the unit you are trying to protect.

[brawlins]

Did a bad backfire blow apart the toilet cover piece? Did the spring not work?

[vash]

wait a second. the hinge from the POV needs to face the rear of the car, right? if you initially had it backwards, the filter would stop it from opening and POW! off it comes.

[brawlins]

The open mouth of the valve now faces the back. It was facing the front.