Rwest, thought I would give you the benefit of my two cents....Had similar symptoms of bucking under load...out of the blue a few weeks ago. 76 Targa (also choc brown BTW)...No, it wasn't too much chocolate....

What it proved to be however, was a simple fix. After checking all systems, (this is a thoroughly updated and functional, 56K mile original motor) I noticed I had wet plugs. Rich. A fellow Pelicaner on one of the various threads talked about airbox leaks, the perpetual debate re pop-off valves, etc., all of which caused me to think systematically... Pulled airbox cover and noticed my cover straps were stretched, cracked, and when ultimately measured against new, approx. 2.5 in. longer than new... Cover was loose. Too much air supplied to meter arm/disc. Strapped down tight with bungees awaiting delivery of new straps...world of difference. New straps installed yesterday, and taken on test drive. Like new. Good power, no bucking. For a $10 fix, it ranks right up there. Give them a look. My fee is a picture of your look alike. Here's mine.

BTW, the red 924S is for sale in the classifieds....

robfleming1@juno.comhttp://forums.pelicanparts.com/uploa...1502881012.jpghttp://forums.pelicanparts.com/uploa...1502881112.jpg

CIS troubleshooting........
 

Rob,

Glad to hear you fixed your running problem. But to seriously believe that the air filter cover strap/s is the culprit is preposterous. Assuming you are correct, excessive air will not cause the system to go RICH and instead go the other way (LEAN).

Sorry for not agreeing with your post. I just find it ridiculous and hope people are not gullible.

Tony

As you may have read, I decided to go with the Bitz kit and have a thread on that, but am still curious why I suddenly went lean, so as I have a chance and particularly if it is needed on the Bitz conversion, I am testing parts.

I dunked the pressurized airbox with intake boots in water and found no leaks.

I hooked up power to the AAR and after it closed up, I blew through it, or rather tried to, it passed zero air when closed.

I'll test the AAV sometime soon too.

Since I was going to be working in the area of the vacuum line to the brake booster, I decided to replace it just in case it was a source of vacuum leak- nope, plugged one end and pulled vac on the other and it held.

Boy, was that a bugger to get out; guess it is good to replace as it is forty years old. Should be fun to thread the new one in too!

Just to update this thread as we all hate when people don't post outcomes.

After putting in the Bitz kit, the backfiring was still occurring, so after trying some tuning, I became convinced that it was mechanical or ignition related.

I pulled all the plugs and #5 was almost completely closed! My fears where confirmed when a boroscope showed a beat up piston top and what appears to be a small screw. Leakdown test was poor and lots of air out the tailpipe.

Looks like some rebuilding in my future.

Rutager

Drivability Issues '77 CIS
 

Sorry to hear Rutager, been following the thread since the beginning... please keep us posted on what you decide to do next.


Thanks,
Saadi

Thanks, I'll be posting updates on my Bitz thread as this one was about my CIS, which is now in boxes!

http://forums.pelicanparts.com/porsche-911-technical-forum/967150-bitz-kit-install-stock-77-911s.html