Popoff valve facing wrong direction. Need some Help.

[Rodek]

My '78 SC airbox popoff valve is getting stuck on the air filter and causing a starting issue. I've done some research and have found the reason to be the popoff valve being installed incorrectly. The valve hinge is supposed to be at the rear of the airbox instead of the front of the airbox. Mine is installed in the wrong orientation. Here's where I need some help.

How do I remove the epoxied in popoff valve to re-orient it?

[David Inc.]

The popoff should only be opening when there's a backfire, and if it's constantly happening then something else is wrong.

[panama911]

I had the same... It would hang on the air filter and let the car die.. However, mine is still mounted the wrong way.
My solution was to get my cis sorted so it just does'nt pop anymore ;-)

(Last time it did was at startup after sitting in freezing cold winter for some weeks.. but normally it just doesnt pop.)

[pmax]

The toilet seat itself could be leaking.

Good info in this thread, an oldie but goodie.
https://forums.pelicanparts.com/porsche-911-technical-forum/976754-pop-off-not-pop-off.html

[boyt911sc]

Originally Posted by Rodek

My '78 SC airbox popoff valve is getting stuck on the air filter and causing a starting issue. I've done some research and have found the reason to be the popoff valve being installed incorrectly. The valve hinge is supposed to be at the rear of the airbox instead of the front of the airbox. Mine is installed in the wrong orientation. Here's where I need some help.

How do I remove the epoxied in popoff valve to re-orient it?

Rodek,

Could you post a picture of the POV? To remove your POV you could use a heat gun to break the adhesion between the POV and the air box. The glass transition temperature of the epoxy or adhesive is well below the Tg of the air box and POV materials. Distribute the heat evenly around the POV and once the adhesive starts to soften, start prying the POV until it separates from the air box.

Tony

[john walker's workshop]

Pop it out with a screwdriver and reglue.

[Marc Bixen]

Tune the car properly, and get rid of the pop-off valve. In the 80's I worked at a shop called "The Factory". We had the patent on the valve, manufactured them, and sold them to all the venders. Every car that came in got one installed. Then I went to work at Red Line in 1995. Pete Zimmermann explained that they caused more problems than they cured. I took over Red Line in 1999 and in the last 28 years i've repaired approximately 5 or 6 blown airboxes total. Usually because the airboxes were very old, and or the cars had a running issue. Not necessary! In your case, if a replacement box is out of the question, I agree with John Walker, Pop it out and reinstall. Just make sure your using a 2 part epoxy that is correct for the airbox material.

[Rodek]

I am very thankful to be a part of this forum. The knowledge, comradery and experience here never ceases to amaze me!

A little more background:

The car doesn't seem to be backfiring however, once in a while it will have a warm start problem. When the warm start issue once occurred, on a whim I went to check the airbox. I undid the straps and as soon as I started to pull the cover (car not running) I heard the popoff valve snap back into place. A few weeks later it did it again. This led me to discovering the valve to be installed with the "toilet seat" opening in the wrong direction.

Plan of attack:

My plan is to follow your suggestions. I'm going to ensure my CIS is properly set up and most likely pop the valve out per your suggested methods and re-install correctly. I'm not currently able to be without the popoff valve installed because I don't have a spare airbox.

[75 911s]

Originally Posted by Marc Bixen

Tune the car properly, and get rid of the pop-off valve. In the 80's I worked at a shop called "The Factory". We had the patent on the valve, manufactured them, and sold them to all the venders. Every car that came in got one installed. Then I went to work at Red Line in 1995. Pete Zimmermann explained that they caused more problems than they cured. I took over Red Line in 1999 and in the last 28 years i've repaired approximately 5 or 6 blown airboxes total. Usually because the airboxes were very old, and or the cars had a running issue. Not necessary! In your case, if a replacement box is out of the question, I agree with John Walker, Pop it out and reinstall. Just make sure your using a 2 part epoxy that is correct for the airbox material.

This 100% The popoff valve is responsible for more tuning issues than it solves.

[PeteKz]

Bah. I've had a POV on my engine for 30 years. No problems.

[997at]

Originally Posted by Marc Bixen

Tune the car properly, and get rid of the pop-off valve. In the 80's I worked at a shop called "The Factory". We had the patent on the valve, manufactured them, and sold them to all the venders. Every car that came in got one installed. Then I went to work at Red Line in 1995. Pete Zimmermann explained that they caused more problems than they cured. I took over Red Line in 1999 and in the last 28 years i've repaired approximately 5 or 6 blown airboxes total. Usually because the airboxes were very old, and or the cars had a running issue. Not necessary! In your case, if a replacement box is out of the question, I agree with John Walker, Pop it out and reinstall. Just make sure you’re using a 2 part epoxy that is correct for the airbox material.

Couldn’t agree more with this. If the car is tuned and maintained I would not put in a pop off valve. However, unless you are installing a new air box then you have no choice but to remove, clean, and reinstall.

[HarryD]

Properly installed Popoff Valve.

[pmax]

Originally Posted by HarryD

Properly installed Popoff Valve.

Yes, if you decide to install the toilet seat, make sure it opens away from you ... or something like that.