Zenith

[workcrazed]

I've gone through my carbs w/rebuild kits, a year ago and of course left gas in them.
Let me go back car sat in garage for 17 years, I rebuilt carbs got her running then took a year getting her make-up finish.
I'm getting some popping back through cyl.1 mostly, and not running smooth at low RPM's.
Valves are adjusted, dwell set timing just a little advanced, 1 deg. can't help myself. So, pulled both carbs off last night again and found 2 accelerator balls gummed up on cyl. 4&5, but nothing I can see to make her lean.
Not exp. on these forums but reading what I can, sounds like I can take off the enricher stuff, off side of carbs and plug vac. ports.
And read about idle ciruit being plugged?

Can ya'll reassure me that I'm ok w/both these ideas?

Thanks 73 Targa, w/ stock 2.4, 60,000 original.

[kkinzli]

I am kind of in the same boat as you are. Currently rebuilding my Zeniths against the advice of everybody who said to scrap them and get Webers. What exactly do you mean by taking off enricher stuff and plugging vacuum ports?

[workcrazed]

On the side of the carbs. there are 3 vacuum lines that go together to a diaphragm and a small vacuum line pulls on the diaphragm to open all 3 lines to the center throat of the carb.
I've read on a different thread that this is smog emission stuff? not for sure what it's for really, that's why I'm asking.

[john walker's workshop]

just screw the big screw in all the way. then balance the stacks and adjust the carbs as normal.

[workcrazed]

Don't have the carbs rebuilt, it's easy to do yourself unless they're badly corroded or have badly worn throttle shaft bushings.

Here's the process:

1) Do only one carb at a time so as not to loss parts as well as to have a reference if you get confused.

2) Clean the outside of the carbs with carb cleaner and spray everything that unscrews with Kroil and let sit over night.

3) Remove the air cleaner and air horns, keep the air horns if they are the same bore as the carb (40mm) as they help HP. Some Zeniths have small air horns which will hurt performance on a larger engine.

4) Remove the screws that hold the top plate anf float assembly and then remove the top assembly.

5) Remove the needle valves from the top assembly as well as the fuel inlets, soak the fuel screens in carb cleaner.

6) Inspect the floats for damage, if they look good then leave them in place and thoroughly clean the top assembly. Do not remove the floats if you don't have to, it's easy to damage them.

7) Now for the base assembly, remove the idle jets, main jets, idle mixture screws, idle air correction screws, screw in plugs next to the idle mixture screws, accelerator pump actuator shaft assembly, accelerator pumps and springs.

8) With the carb facing up you'll see 3 accelerator pump squirters, these have hex head but do not unscrew and they are very fragile, give them a good soak with Kroil and CAREFULLY pull them straight up and out. DO NOT force them out, if you have trouble soak them longer. Sometimes the O-rings around them get stuck. Once they are out flip the carb over and shake out the accelerator pump check valves, they look like small nails.

9) Remove the boosters, these are retained by spring clips, jsut wiggle them back and forth while pulling up on them. You'll notice the boosters have a slotted hole on one side the lines up with the emulsion tubes and main air jets, remember to put them back in this way.

10) Remove the main air jets, flip the carb over and lightly tap on a wooden block so that the venturis and emulsion tubes drop out.

11) If the carbs still have the aux. enrichment circuit remove it and all its vacuum lines. You won't been needing this so either toos it or put it somewhere out of the way.

12) now you've got a basically bare carb with the throttle plates still in place. It's best to leave these alone if they are in good shape. Inspect the shafts for wear, especially the one on the linkage end. If worn you'll need a machine shop to install new bushings, I made my own and I'm considering offering this as a service if I ever get caught up. Any decent machine shop can press out the old bushing and install new ones. I've never check to see if there is a commecially available bushing as they are easily made on a lathe.

13) If the shafts look good check to see if the throttle plates are all equally closed, if not there are collars between the shafts to readjust them. It's critical they all line up for proper tuning.

14) Using a very flat surface check that the base of the carb is flat. if not you can draw file or lightly sand on a table sander to get them flat. I always give them a light touch up on the sander with fine grit to avoid vacuum leaks.

15) Using lead shot plug the tree large vacuum tubes on the mixture screw side and the small one near on the other side. On a pair of Zeniths the right side carb has a solenoid for the enrichment circuit, rather than make a plug I just reinstall it during reassembly, just leave it unhooked for the wire if present.

16) There is a hole near the top that was behind the enrichment valve, this will need to be plugged, I generally tap it for a standard bolt and loctite a bolt in there, a set screw would also work but use loctite to seal it.

17) Look down into the float bowls, there are small jets that are a pain to get out, I normally just clean these with carb cleaner, small wire and compressed air. Same goes for the idle air jets which are located on the base assembly top near each idle jet.

18) Thoroughly clean everything you've removed with carb cleaner as well as the top and bottom assemblies. Use compressed air to blow out any passages, especially the idle passages and the idle holes that where covered by the screw in plugs near the mixture screws.

19) give the top and bottom assemblies a good visual inspection, you want everything to be clean a free of varnish/residue. If there is any question soak them in a covered plastic container full of carb cleaner at least over night.

Reassembly and adjustment to follow.
__________________
Email me about 911 exhaust stud repair tools,rsr911@neo.rr.com
1966 912 converted to 3.0 and IROC body
1973 911T tub, will be stripped to the bone, G50, etc.
2003 Expedition XLT loaded with DVD for the kids. 9000lb towing capacity for daddy's toys!

[workcrazed]

Reassembly is essential the reverse of removal. Here's my method:

1) Thorougly dry the assemblies with compressed air.

2) With the bottom assembly sitting face up, install the venturis, the boosters, the emulsion tubes and the jets that cover them. Leave the pump squirters and check valves out for now.

3) Install the idle and main jets, install the screw in idle passage plugs, idle correction screws, idle adjustment screws (install new O-rings on these).

4) turn the carb around and install new accelerator pumps. Put the springs in first then put the pump diaphragm and cover on, don't over torque the covers. If they are warped sand them flat on a piece of glass.

5) Install the accelerator pump actuator bar, loosen the adjustment screws and adjust them all equally. You want the adjusters touching with the throttle shut. Now preadjust the roller bar that rides on the linkage cam and actuates the pump actuator bar. Ideally the pumps will move as soon as you crack the throttles open. At this point the pumps are setup for max flow which works well with larger engines. You can lessen the flow by adjusting the pump adjuster to compress the pumps more but do all three the same. I leave mine on max flow.

6) Flip the base upside down and adjust the idle speed screw so that the throttle plates are just barely open, this will be your baseline for later adjustment.

7) With the base right side up again install the gasket that goes between the assemblies, then drop in the accelerator pump check valves, the head faces up. Install new O-rings on the pump squirters, lightly oil them and gently press them in.

8) Install the top assembly to the base assembly and install the screws, don't forget the spring tab on the screw near then linkage.

9) Install the needle valves. These are adjusted for float level with gasket shims, I install only one shim at first. Install the screw on covers for the needle valves.

10) Install the inlet screens and fuel inlets. (If you have a high quality fuel filter in the engine bay you don't need the screens)

11) Optional, install vacuum caps over the vacuum tubes you plugged with lead shot, added insurance if the lead shot where to vibrate loose.

12) One down one to go, do the other carb the same way.

13) Install and properly torque the manifolds to the engine, if it was a CIS motor you definately need the phenolic isolators to prevent a vacuum leak due to the relief in the port for the CIS injectors. I learned this the hard way. With them manifolds installed check with a straight edge to make sure they are flat. A warped manifold that is not fixed will drive you crazy! If warped remove the studs and use a table sander to flatten it, if the heads aren't equal for some reason and they are causing it to not sit flat then your best bet is to double gasket under the manifold and use gasket adhesive.

14) Install the carbs, linkage bar and fuel lines.

Setup to follow
__________________
Email me about 911 exhaust stud repair tools,rsr911@neo.rr.com
1966 912 converted to 3.0 and IROC body
1973 911T tub, will be stripped to the bone, G50, etc.
2003 Expedition XLT loaded with DVD for the kids. 9000lb towing capacity for daddy's toys!

[workcrazed]

Ok now your carbs are on the engine, don't hook the linkage to the carbs just yet.

1) Using the float level tool available from our host install it in place of one of the float bowl plugs and turn the key to run to fill the bowls. Check and adjust float level as needed. The level is raised by adding shim gaskets under the needle valves. Repeat for all four float bowls. It's a good idea to install a pressure gauge and regulator, pressure should be 2-3 PSI.

2) Install the linkage, adjust the rod at each carb so it goes on without moving the crossbar or the throttle plates.

3) Adjust the correction screws all the way in and the mixture screws 2.5 turns out.

4) Have an assistant start the car, you'll likely have to blip the cross bar to keep it running at first, adjust the idle speed screws equally on both carbs until the car will idle and let it warm up.

5) Once fully warm use a carb sychronizer to balance the carbs side to side, this is done by adjusting the speed screws, you'll want and idle around 1000-1200 RPM at first.

6) Check each barrel to find the one with the highest reading, leave the correction screw closed on this one and adjust the other 5 to match, you may have to do this a few times to get it right.

7) Now go for a short test drive, if the car surges at light throttle or pops a lot on decel the mixture is too lean, adjust the screws out 1/2 turn and try again. if you need to adjust them more than 3.5 turns out your idle jets are too small. Check throttle response it should be crisp, if not adjust the accelerator pumps until it is. Start by adjusting the roller lever first followed by the individual pumps if need be. Be sure to adjust everythig equally.

8) Now that the car is running decent reduce the idle speed to 800-900 RPM, recheck the side to side balance and adjust accordingly.

9) Congratulations you've just rebuilt and setup your Zenith carbs. Some opt to use a gas tester to adjust the idle mixture, I like to leave mine on the rich side for a smooth transition circuit and zero decel popping. Check your plugs, if too black lean it out a touch, likewise if they are white its way too lean so richen it up. Ideal plugs are a light tan.

10) Adjusting main jets can be done by feel but is best done with an O2 sensor and dash mounted gauge. Better still would be a dyno run but bring spare jets!

11) Remember those air horns? If you're using watershields install them inside they smooth out the airflow through the carb and boosters and really help power and drivability. If your originals are too small I believe PMO sells them. PMO, Weber and Zenith all have the same bolt spacing for the air horns and air filters.

Lastly if the throttle response and drivability doesn't absolutely thrill you you've done something wrong. Go back and recheck the setup.

Enjoy!

[workcrazed]

A Quiet Boom THANKX!!!!

This has probably been repeated many times, took me 8 hours to find.

What awesome info.

73 911T RS Getting There.
78 928 Got there, Was FUN, Sold It.

[pcar9119]

If you buy the book " Porsche 911 Performance Handbook" He gives you all the formulas for figuering out what you need, it isn't as much guess workmas people make it sound.

[kkinzli]

workcrazed. I did rebuild both of mine myself. Wish I would have had your write up but I ended up doing the same thing just learning the hard way. I am still a little confused as to which holes need to be plugged up. Could you possibly post a picture? Thanks