recently brought '72 911T to life again but need help

[traderdan]

Just recently unseized a '72 T motor and got her running again and was assessing how far into a rebuild I wanted to get into. The car takes quite a bit of cranking to get started and backfires and misses a lot to get started. once it's ran for a bit it smoothes out but starts bucking wildly and missing when hitting 3000 rpm. Seems to run fine at steady rpm in between with an occassional miss, then the whole engine seems to cut out (about 1000 rpm) and then goes back up 1000 rpm - this pattern continues again and only stops when the car is shut off and then goes away when restarted but still bucks at 3000 rpm and backfires. Also won't idle most of the time, changing distributor position while running I was able to get a 3-400 rpm idle for about 1 minute or so but thats it. The mfi was cleaned out and the velocity stacks were seized and I got them moving again when I took the motor out the first time however they looked pretty darn worn in my opinion, however my first concern is the distributor which I replaced. The one on the engine was shot to heck and I found one on eBay on the cheap that supposed to be off another '72 T but not 100% sure, it looks identical at least. My instincts tell me that the disturbutor and/or advance is wrong ---- timing or spark related problems and MFI problems second. ---- I also noticed some pretty hard tapping sound from one of the valves compared to the other 5 when I put a large pipe to the motor with my ear on it but it's not noticable otherwise. I'll probably rebuild this motor anyway but this is the first porsche I've ever worked on and I'm still a newbie when it comes to auto repair but I love the cars and always wanted to know how they worked. Just thought I'd work on this idle problem for some practice and learning and might even help assess what points to take care of in the rebuild. Any advice would be greatly appreciated as always. again sorry for the long post ^_^

[Early_S_Man]

Dan,

Any '72 thru '77 distributor will work fine in your engine ... all have the same advance curve ... which is posted in the following thread:

distributor lube...

An 'advance-type' timing light is a big help to check the advance curve, and the curve is shown both in graphical form and chart form at specific rpm steps in the above thread.

[traderdan]

That thread was very helpful, thanks Warren - I'll add it to my favorites list.

Aside from checking the distributor and the ignition timing any other places I should start?

[jim72911t]

Dan,

I've got a '72T and my car displayed some of the same symtoms as you describe, although it's tough to know exactly what it's doing by your description alone.

I would recommend a full tuneup and downloading a copy of Check, Measure and Adjust so you can troubleshoot and adjust your MFI.

I'd also check the compression. I was getting no power above 3-4000 rpm and it turned out that my P/C's were shot, among other things
)

This board is a great resource and can guide you through just about anything you need to do.

Good Luck,
Jim

[Zeke]

Originally posted by traderdan
I'll probably rebuild this motor anyway but this is the first porsche I've ever worked on and I'm still a newbie when it comes to auto repair but I love the cars and always wanted to know how they worked. Just thought I'd work on this idle problem for some practice and learning and might even help assess what points to take care of in the rebuild. Any advice would be greatly appreciated as always. again sorry for the long post ^_^

"...and I'm still a newbie when it comes to auto reapir...." I had to quote that twice, once in context and once out. Before you rush off to rebuld the motor, I suggest taking some time to see what you have there. Do or get a compression check and a leak down test. Get the thing on a scope and get the timing in spec. If you want to work on the car yourself, then download the CM&A suggested above.

I've been working on cars for 40 years as a hobby. I'm not a pro, but I have tools and good skills. Porsche MFI motors are a challange even for the well initiated.

I too, brought a has been back to life and it also had the same frozen butterflys. I have gotten the thing to run fairly decent with some time and effort. Some of the problems you descrbed appear to be MFI related as I faced the same ones. Work with it or get some work done before tearing the motor apart. Remember, after you have spent $1000's on a rebuild, you still have the same distributor and fuel injection to reinstall on that engine. Might as well get them taken care of first.

One more thing, many of us have had super results just changing out old spark plug wires and spark plugs. Especially on a car that has sat long enough for the butterflys to freeze. I don't have to tell you about fuel filters and fuel lines (I hope).

[traderdan]

Okay thanks guys you're a great help I don't think I would have gotten even this far without the tech board or pelican parts. Umm what does jim mean by P/C's?

I do take it that the check measure and adjust FAQ can be found on the pelican site?

[Zeke]

P/C's = pistons and cylinders.