911T Zenith carb help !

[blackbird225]

For those who don't know yet. I just got my very first Porsche today. A 70 911t. It does indeed have the Zeniths. The car was recently tuned , however it was tuned in Alberta Canada. I am at sea level. I have a book on Webers and Zeniths coming in the mail, but I was hoping one or some of you could shed some liget on what to do.
It is sputtering and idling rough. It smells rich, as I can smell a little unburnt gas in the exhaust. No white or blue smoke .. whew! A fully rebuilt engine\transmission.
I have the Hayes manual (which I head sux) and there is a very short essay on enriching the carbs.
PLEASE PLEASE advise,

TIA
Michael

Also, there is not a single oil drip, but the the oil tank looks wet with oil leak, is this natural?

[Tyson Schmidt]

What's the elevation in Alberta? Were any jets changed?

If it was set up for altitude, and you are now at sea-level, then the carbs will be too lean, not too rich.

As a quick fix, you could back out the idle mixture screws on all 6 throats in 1/4 turn increments until it gets better. Then pull out the idle jets and compare the number on the jets to what the Haynes manual states as the stock jet. There is a section in the fuel system chapter that gives all the venturi and jet sizes for each model year. The Haynes manual is actually pretty darn good for carbs.

[901/05]

too me. I am familiar with jetting lean for high above sea level, but not at all familiar with the zenith carbs and thier jet stages.

I am quite impressed with Tyson's expertise and accomplishments regarding early 911 tuning (mostly due to this bboard and Jack Olsen's postings).

I am jumping on your thread here because I am presently negotiating the purchase of a 70T with zeniths as well.

I would love to hear Tyson's thoughts on the zeniths. Most 70T owners upgrade to webers carbs or spend the big $$ for MFI. I am wondering if the zeniths are really so bad after all.

Hopefully, I haven't hijacked your thread and Tyson will give us all his tuning information and experience for free. Most of his customers are required to contribute to his paycheck via his shop. Just which shop is that BTW?

Shawn.

[Allenk]

I also have the Zeniths and it took quite a while to learn and pick up on their behavior. Once right, I think they are very good. There are several posts related to tuning and it would be worth checking before going through it all again. There are some very detailed tech articles that almost "hand-hold" you though the process an if you carbs are in good sape with no other mechanical issues, you'll be running in no time.

[steveW]

My theory.

Zeniths are now 32 years old. Butterflys, shafts etc are all worn beyond economical repair. Feel the play in all the linkages and you'll see what I mean.

The same also applies to Webers.

I've written to Santa for some PMOs.......do you think he'll get my letter?

[Allenk]

Although that may be true, I would not give up yet. The Zeniths on my car where as SteveW described, but only 1( don't ask me). I got a donor set and replaced the shafts and good to go. Personnally from my experience, I would take them off and as a minimum, line up all the "butterflies" and set the carbs to factory specs and check for slop. If they are sloppy, then your sucking air and can spend the rest of you life never getting them right. A PO could have monkey with things and Zeniths can go bad fast if the proper tuning steps are not followed.

[blackbird225]

Yes, but the PO didnt do any of the work himself. A classic Import shop in Canada did all the work, and the PO stated that the car ran and purred like a kitten. There is very little slop in the linkage or none. You can see new gaskets at all of the matings. He WAS at a very high altitude. I plan on richening up the carbs a little tonight, but what might I expect to pay for a local shop to do the work?

TIA

Michael

[Allenk]

Just do as Tyson suggested and remember your starting point. Popping thru the carbs is usually lean, thru the exhaust is rich. I think the fuel smell may be from the carbs popping and putting the smell in the air. If Tyson' s idea doesn't work, I may have some spare jets you can work with. An easy exchange. No idea on shop cost.

[si2t3m]

Well basically, say that the carbs are in sync and all and still runs like crap once the car is warmed up (when the engine is cold and with carbs, it's kinda normal that it runs like crap till it's warmed up a bit).

So if it's running like crap at idle when it's warmed up, stop the car and get a pen and paper and turn in each idle mixture screw (the one that is spring loaded) counting the number of turns till it closes. This way, you will be able to go back to the initial setup. Back them all to where the were initially and back them out again 3/4 of a turn.

Take the car out warm it up a bit (just don't let it idle to warm it up). Let the car run and start turning in the idle mixture screw for #1 cylinder by 1/8 increments waiting at least 10 seconds to see if the rpm drops. Keep on turning it in like this the rpm drops. As soon as the rpm drops, back out the idle mixture screw 1/2 turn. (If for some reason you completely turned in the idle mixture screw and nothing happened, something is fishy in the idle circuit or ignition or something else) Repeat the procedure for each cylinder. This should do the trick.

HTH

Marc-André

[blackbird225]

Sounds like Tyson is the man, so I will do as he suggests. Also, The E brake is shot, is it fairly easy to adjust?
TIA

Michael

[Allenk]

si2t3m makes a good point, if turning the mixture screws yeilds no result(meaning change in idle), something else is wrong, either with the idle circuit or ??. I had this problem and it turned out that the P.O. compensated for poor idle by adjusting the idle screws. This caused fuel to be drawn thru the transition circuit basically by-passig the idle circuit. I could turn the idle screws completely in w/o any change in the way the car ran. What a mess.

[nigel911]

Emergency brake is an easy fix, one of 3 things: shoes worn, adjuster by handbrake out of balance (does the brake work on only one side?) or the shoes needs adjusting at the hubs to compensate for wear.