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Replacing Zenith Carb Top Cover Gasket

September 27, 2010 | Troubleshooting & Repair

A Newbie Pulls a Carb — and a few other things

By Steve Dempsey, with a lot of help from Ron LaDow and Tom Farnam


I live in south central Missouri where 356 expertise basically doesn't exist. The nearest shop recommended by fellow 356ers is in St. Louis, about 160 miles away. Recently I discovered the top cover gasket on my driver side Zenith 32NDIX carburetor leaking. Since I couldn't just drive over to a shop and drop the car off, I sent an e-mail to 356Talk to find out if I could replace this gasket without removing the carburetor, something I really wasn't confident in my ability to complete successfully. Although I was assured by several on the list that this indeed could be done, the consensus was that the job was easier if I removed the carburetor. I decided to give it a shot, and as it turns out, this job is really something anyone with basic skills (and a little muscle) can handle. No magic!

Tools Needed

  • "Wide" screwdriver or 14 mm socket and long extension
  • 17 mm box/open end wrench
  • 10 mm box/open end wrench
  • 12 mm "stubby" box/open end wrench (mine is 4 inches long) – unless you just happen to have Porsche tool P23 handy
  • Paper Towels

The Procedure

BE SURE TO EXTINGUISH ANY OPEN FLAME IN YOUR GARAGE - WATER HEATER, FURNACE, GAS CLOTHES DRYER, INCLUDING THE PILOT LIGHTS FOR ALL OF THESE, AND SHUT OFF ANY ELECTRONIC IGNITERS USED ON SIMILAR APPLIANCES IN LIEU OF A PILOT LIGHT. YOU WILL HAVE SOME GAS FUMES, AND THEY CAN BE EXPLOSIVE.

  1. Close the fuel cock — all the way to the left in the "Z" position. This is the same position in all 356 cars, but this handle can be accidentally be installed 180 degrees out of phase — it can point to "Z" and actually be in the reserve position. The handle must be rotated counter-clockwise until it stops.
  2. Remove the air cleaner. My car has the Knecht "black cans". Under the bottom of the can you should find a 14 mm nut to loosen with either a wide screwdriver or the 14 mm socket. Lift the cleaner straight up and off. I found that twisting the air cleaner a little side to side helped. If you have a 356C you may have an 11 mm hex bolt.
    CHECK AGAIN TO BE SURE THERE ARE NO OPEN FLAMES IN THE GARAGE!
  3. Next you need to disconnect the fuel line that runs between the fuel pump and the carburetor. Find this line and you will see that it ends in a 17 mm connection. Use the 17 mm box/open end wrench. There should be two red washers when you pull it loose from the carburetor. Don't lose these! There will likely be some gas leakage as the top of the fuel line drains. Catch it with paper towels (like I did), or with aluminum tins.
    Note: Do NOT put a lot of strain on these bolts with that big 17mm wrench. These are hollow bolts going through a "banjo" housing at the end of the fuel line, and the carburetor is a "pot metal" casting, not very strong. Remember, righty-tighty, lefty-loosey (as you are facing these bolts).
  4. Using the open end of the 10mm wrench, "pickle fork" (I'm stealing this description from Ron LaDow) the links off the ball-ends.
  5. OK, now we are getting serious. Grab the 12 mm wrench and remove — carefully to avoid damaging or breaking the idle adjustment screws — the four nuts holding the carburetor to the intake manifold. There will be four washers as well. Believe it or not, there is plenty of room with a short 12 mm wrench to get behind the carburetor and remove these nuts. Save all the parts!
  6. Now the muscle part begins. The carburetor should lift straight up and off the studs. If it doesn't, it is probably stuck to the gasket. Try tapping the beast with the palm of your hand a few times. If that doesn't work, you can get a small piece of 2 x 4, place it against the carburetor at the large open area between the top and bottom portions and tap it a few times with a small plastic or rubber hammer. It will break loose.
  7. Congratulations! Your carburetor is now off and you can proceed with whatever task you have in mind. Take some paper towels and jam them in the intake manifold. Don't wait — fully cover the intake manifold right away — it's amazing how quickly a washer or nut can fall into that hole.

Top Cover Gasket Replacement


Photo courtesy PrecisionMatters
As mentioned above, my particular reason for removing the carburetor was to replace the leaking top cover gasket. However, I didn't want to mess up the synchronization of my carburetors because I'm happy with them like they are and I've haven't tried yet to do that job. After asking the experts if what I wanted to do was possible, I made sure when I was disconnecting the links in step 4 above to leave everything exactly as it was.
  1. Before taking the top cover off I cleaned up the exterior of the carburetor as best I could. I used WD-40 to do this (is there anything this stuff won't do?). Another suggestion is to use lighter fluid to keep the WD-40 from going places you might not want it to.
    Note: I cleaned the bottom as well, removing the old manifold gasket and making sure to get rid of all remains of it in the process.
  2. Remove the clip, washer, and spring from the pump linkage (pay attention and don't lose these — they are hard to find when they go flying across the room, trust me) and unhook the linkage. I used a pair of needle nose pliers for this.
  3. Remove the screws/washers holding the top cover down. An 8mm socket or driver is best (since it won't bugger up the screw slot), or, in an emergency, a regular slotted screwdriver will suffice. Don't use long-handled drivers. Do this gently — this is pot metal, and not easy to repair.
    Note: Make sure to check the position of your throttle return spring. It needs to go back on the same way.
  4. Remove the cover. Mine was stuck, of course, and I had to use a small rubber hammer to tap the underside of the fuel line boss (the area that protrudes from the carburetor where the fuel line attaches) gently a few times to get it off. A better thing to do this with is a small plastic "dead blow" hammer from your FLAPS. I didn't have one so I used rubber.
  5. Remove the old top cover gasket and clean off all remains on the top cover and the float bowl of the carburetor. Be careful as you are doing this. You don't want to get flakes of junk into the internal passages of the carburetor. Work towards the outside edge and be conscious of where any debris is going.
    Note: I'm told that this gasket, in some cases, might be held down by a couple of rivets. If so, I'm also told they are easy to remove and replace. In my case, the carburetor did not have these rivets.
  6. Place the new gasket in position, refit the top cover, and replace the screws/washers. GENTLY — get them tight, but don't lean into them as they are threading into pot metal.
  7. Reattach the pump linkage.

Reinstalling the Carburetor

  1. One more cleaning job. If you haven't done this already, clean the area on the intake manifold where the new gasket goes. It is also a good idea to clean the studs and nuts/washers while you are at it.
    Be VERY sure the manifold is plugged before you do this.
  2. Remove the paper towels you jammed into the intake manifold. Place a new intake manifold gasket into position.
  3. Gently place the carburetor over the studs. Spring is facing you!
  4. Replace and tighten the nuts and washers. A little reminder here to once again be very careful tightening these with your 12 mm wrench to avoid breaking or bending the idle adjustment screws. In my case, I just made 100% certain that the wrench never touched either of these screws and got things tight by using lots of very short pushes on the wrench. My 4 inch wrench gave me plenty of leverage, but I had to pay attention.
  5. Snap the links back onto the ball-ends. In my case (thank goodness), no adjustment was needed, and that is good because as mentioned before I wanted to preserve my existing tune.
  6. Reattach the fuel line running from the fuel pump to the carburetor — don't forget the washers! One washer goes on each side of the banjo fitting — and once again, take it easy with that big old 17 mm wrench. These need to be tight, but not broken.
  7. Reinstall the air cleaner. You might have to twist it again to get it on.
  8. Turn on fuel cock.
  9. Start the engine! In my case, I was thrilled to find that the engine fired up immediately and ran exactly as it did before I started — minus the leaky top cover gasket, of course.

2 Comments

Aa493c9f9299cdb0d51a6d201e2b655c 3805
Richard Viren
December 30, 2010 at 7:51 PM
Steve, I too live in south central Missouri and know the lack of anything 356 you speak of. Thanks for the article.<br />Richard Viren<br />60 coupe 1600 super<br />Waynesville, MO
Aa493c9f9299cdb0d51a6d201e2b655c 3805
Richard Viren
December 30, 2010 at 7:51 PM
Steve, I too live in south central Missouri and know the lack of anything 356 you speak of. Thanks for the article.<br />Richard Viren<br />60 coupe 1600 super<br />Waynesville, MO