Zenith carb question - 71 911T 2.2

[Mat 71]

Hi, haven't had much questions to post up until this point, but love the forum and information available.

First time owner of a '71 911T 2.2L with Zeniths. Should be a picture. I bought the car with the engine out on the word of the older gentlemen that the car was running when engine was pulled (I know what a lot of you are saying, but I like to live life on the edge sometimes and needed a project). Turns out he was right as after getting the electrical figured out over the winter, and some fuel down the carbs it started. Lots of smoke as one would expect, but after running for awhile and drained fuel tank a couple more times, it started better everytime. Did take some time and cranking though.

Brought it from one shop to my garage on the trailer and and it won't start now...hmmmm. It hadn't been started for about 3 weeks prior to this. That was 5 weeks ago. Since then I have pulled the carbs and re-cleaned them, put them back on. Taken the tops off to re-clean the injection tubes and re-set the plungers on the pumps. Had very good flow from all 6 tubes at that point. I re-installed the tops and cranked it over. By manually pumping the throttle and putting fuel through the carbs I would get it to want to start. Closest I got was a very weak idle for about 20 seconds. I went back and noticed one of the fuel lines was leaking to the driver side carb. I replaced them this morning and in my infinite wisdom decided to re-adjust the idle mixture screws to 2 1/2 turns out each. NOTE: I have not had much experience with carbs. I then took out the air by-pass screws to re-clean and blow some carb cleaner and air into the passage and found something odd. Driver side screws were intact, but the passenger side screws were all "sheared" off? After closer inspection I noticed that their appears to be a removable pin 3/4 of the way down the screw from the top?? Anybody seen this before? I think the other 1/4 of the screw is still in the hole. I assume that this is not the way this should be? If anyone has any thoughts about all of this I would greatly appreciate your help!.

Thanks in advance.

Mat

[FrayAdjacent911]

Not much help, but get some techron through the fuel system. Seems to have helped a little with my Zeniths. You might need a couple tanks with a couple bottles through to clean 'em up.

Otherwise, you might need to rebuild them.

[tswaney]

If I remember correctly, the air bypass control screws have a nylon(?) insert that holds them where you set them. Seems odd that all 3 on one carb would get sheared off, unless they got cranked down with some very high torque.
I offer no advice on how to get the broken tips out.

Could you rev it up beyond the idle range so that the main circuit kicked in? Would it keep running with a few thousand RPM? The idle circuit isn't too complex and you may try taking out the idle jets from each carb and shooting some cleaner into that passage and making sure the jets are clean and open.

When I rebuilt my Zeniths last year, the o-rings on the idle mixture control screws were shredded junk, which I feel led to some of my idle problems.

It may be time for a full rebuild.

[Mat 71]

I will take a picture of the air by-pass screw so you can see it. My picture is not that good, but you can see the groove on the end. When I inspected the intact ones, I noticed that there was a 'dowel' on each of them. I placed one beside the other and noticed that the dowel is out, and the other half is probably still in the hole. One bank of carbs I can spray cleaner through, the other is blocked where the half screws came from. Seemed weird to me as well that one side (3 screws) would be like that.

I forgot to mention that the enrichment valves have been taken off the carbs and I assume that was done right. Should the enrichment solenoid still be hooked up? Would I have a vacuum problem if those holes are not closed properly?

I did not take the idle mixture screws out all the way to notice that there was a washer on them. I will look, but I am tending to think that a complete re-build is in order too. I will order the kits today.

Any tips or hints on the rebuild as I would like to do this right. I have asked AllenK if he could email me the information that he has on these carbs which I think will be useful.

Mat.

[tswaney]

The information that Allen has is excellent, particularly for parts identification and getting the carbs tuned once the carbs are installed after rebuild.

My aux. enrichment system is hooked up and it's purpose is to cut down on emissions when you let off the throttle above certain RPM. I never adjusted it after my rebuild, however. I would plug the 3 nipples on each carb.

The rebuild itself isn't too painful. I took lots of pictures and kept every part in marked Ziploc baggies.

Keep asking questions as you go, and you will certainly find help here.

[Mat 71]

Thanks guys,

Ordered the rebuild kits for the carbs and am going to try and start fresh. I know where to go if I get stuck!

Thanks,
Mat

[sammygon1]

I have Zenith schematics. If you want them send me your email.
-Sam