Zenith carburetor gasket question?? - PeachParts Mercedes-Benz Forum

rgnprof · #1 07-28-2007, 11:53 PM

I finally got my car started but it won't idle and it isn't running right. I adjusted the timing and with my wife keeping it running I was able to get the timing light on it and make some adjustments, which helped with the backfiring.

I did notice serious gasket leaks around both the front AND rear zeniths - spraying carb cleaner indicated leaks at just about all of the mating surfaces, especially between the intake manifold and the carb base. I reused all of the gaskets - they looked in good shape but I'm sure that was a mistake. I posted earlier about the flange gaskets at the manifold and I think I figured out what I did wrong.

Question: Are there paper gaskets that are supposed to go on those thick, phenloic gaskets? I noticed that 3 came in each of my rebuild kits and I found some spare phenolic plates ones that still had the thin layer of paper stuck to them. If so, where do I install just 3? 4 would make sense - one on each side of the 2 phenolic gaskets. Maybe you just use 2 - one that sits directly on the intake manifold and the other on the carburetor?? And the third is just a spare?

Ryan

nhdoc · #2 07-29-2007, 10:37 AM

Mine had no gaskets and none is shown on the EPC. It simply shows the heat shield sandwiched by 2 insualting flanges and no gaskets. I am thinking I'll use some high-temp gasket goo the next time I assemble mine to ensure there are no leaks though.

cth350 · #3 07-29-2007, 11:22 AM

My personal position, take it for what it's worth, is that those little paper gaskets for the base are useless.

You can and should replace the phenolic parts with the real thing. Especially the kidney shaped one that connects the bowl to the base, as I don't trust that thick piece of cardboard that comes with the kits to survive as long as the original.

You can recycle the phenolic parts. Note that the surface isn't smooth. That's why new ones come with a paper mating surface. It's quite thin, rather than the gasket that comes in the kit. Almost like a sheet of writing paper.

The few times I've recycled the plastic part, I've used a good high heat tolerant sealant. However, I've never followed up on those. When I wanted a zenith job to last forever, I've replaced the parts.

-CTH

rgnprof · #4 07-29-2007, 04:10 PM

None of my schematics show any gaskets either, but on my old phenolic, insulating plates there is clearly a thin layer of 'paper' that you can scrape off with a razor blade, very brittle. I was not planning on replacing the phenolic plates with the kit gaskets - rather I was going to use those gaskets, one on each side of the old phenolic plates.

CTH - I'm a little confused - can I reuse the base phenolic plates or not? They are clearly leaking right now, so should I try the gaskets that come with the kits? They are thicker than the layer of paper that is on the old phenolic base plates??? I did find an online supplier for the carb base plates, about $11 each.

I also reused the kidney shaped one, but I do have the kit ones (thick, cardboard - that is also why I reused the old ones). Are the dealer ones much different - although I haven't been able to find these anywhere except in the kits??

Ryan

Mike D · #5 07-30-2007, 09:16 AM

The Solex's I have on my wife's car are different from your Zenith's but they have the same basic set-up. You MUST use the phenolic spacers. They provide themal protection for the carbs.

I traced the outline of the gasket onto a sheet of gasket material, cut 4 of them , applied a thin coat of gasket tack, stuck them on both sides of the spacer and re-installed.

If the kit has 4 of them then you can use those.

If the kit only has 2 then they were for beneath the original metal heat shields which are probably long gone, tossed by a previous rebuilder.

rgnprof · #6 07-30-2007, 10:19 AM

Thanks, Mike. My question was not about whether or not I needed to use the pheloic insulators - I really want to know if the old ones are reuseable? Or do I have to get new ones? The old ones seem intact, but the thin paper gasket is breaking off.

I have 6 gaskets the same shape as the phenlic spacers - 3 come in each rebuild kit. And I still have the heat shields - I might try and track down 2 more gaskets.

Also, the kidney shaped gasket that comes with the rebuild kits is not quite the same size as mine. My Zenith is a 32/40 and the replacement gasketes are for a 35/40 - I'm not sure if they would fit right. My old ones look good though, but they were leaking some??? Maybe some sealer would help?

ryan

Mike D · #7 07-30-2007, 10:49 AM

The spacers, unless they are obviously cracked through or crumbling from age and excessive heat, are just fine.

On my spacers I scraped off the old thin paper with a razor blade and gave them a quick "surfacing" on some 800 grit wet/dry paper on a piece of glass. I applied some gasket tack and then placed the gaskets on each side of the spacer.

Three gaskets are the right amount. One between the manifold and the heat shield (hah!) and the other two on each side of the spacer.

If you are going to attempt to seal the old internal gaskets do NOT use silicone gasket maker stuff. It is not designed for constant contact/immersion in gasoline. It will swell up and break apart. Small pieces will migrate into your carburetor internally and clog some vital passage at three AM in the morning , on a Sunday, on a rainy day in Waredahellarwe, Nebraska.

Use a "high tack" type of sealer designed for contact with petroleum products.

rgnprof · #8 07-30-2007, 11:46 AM

This car actually has 2 phenolic spacers per carburetor - sequence is intake manifold, spacer, heat shield, spacer, and carburetor. That's why I was having trouble figuring out how to make 3 gaskets work - it seems that I need 4 gaskets per carb, one on each side of the 2 phenolic spacers. Right?

ryan

Mike D · #9 07-30-2007, 12:31 PM

Yeah, you probably should use four in that scenario. Most likely, when everything was new, the thin heat shield itself acted as a gasket.

230/8 · #10 07-30-2007, 12:32 PM

Yes...a gasket each side of the spacer.

230/8

rgnprof · #11 07-31-2007, 04:10 PM

Thanks for the replies - I'm making some progress. I think I got all of the gasket vacuum leaks repaired and I can get the car started and as long as I keep my foot on the gas, it runs great!

I can't get it to idle and now I've got gas dribbling from both carbs. I know I'm way out of balance, I just don't know how to get back on track if I can't keep the thing idling.

ryan

Mike D · #12 07-31-2007, 04:30 PM

Here's a beginning step.

Disconnect and plug all vacuum lines and the acc. linkages from both carbs at the throttle plates. Turn the idle mixture screws all the way in until snug, not tight but snug, back the mixture screws out 1 and 1/2 turns.

Look down the throat of each carb and use the idle adjustment (not mixture screws) screws to slightly open both butterflies to the same position. I use a small drill bit as a gauge on my Solex'es. A long small screwdriver would probably work as well.

Attempt to start the engine. It might fire right off. If it does, slip the Unisync onto each carb and fine tune your idle speed setting. Don't worry if the idle is too high, you will be able to adjust it. You will find yourself going back and forth between idle mixture and idle speed settings. I use a vacuum gauge on each carb AND a pair of Unisyncs for this step. Patience, a gentle touch and a good bar tab is needed for this phase. Double check your final readings by switching the vacuum gauges and Unisync. Go for the best average readings (closest matches between the gauges).

Once you have the carbs sync'ed you are ready to piss about with the linkages. ANY adjustment you make with the idle speed settings must be duplicated on the other carb once you have it sync'ed!

230/8 · #13 07-31-2007, 04:46 PM

Ryan:

You can get your carbs to a basic run condition like this:

The basic setting for starting and running: Disconnect the connecting link between the carbs. Each carb has another link, about 2 inches long with ball connections at each end and an adjustment in the middle. This small link connects each primary throttle with the main carb linkage bell crank so you can convert front-back motion into up-down motion. Set the length of these small links so the primary throttle is fully closed and just about to open. Then open each one-half turn. Then, set idle mixture screws evenly at 2 turns open. This is the basic setting so you can start and run the car.

Once you have made this setting, you can use the carb bonnet and Unisyn tool to set the balance for the pair of carbs. Then you can connect the link between them and move on to setting the dashpot for proper curb idle etc.

If, after balancing, etc., the fuel still dribbles from the carbs, you have a fault...like a leaking float valve or float setting too high.

You should search this site for "balancing Zeniths" to find a mother lode of solid data on the care and feeding of these old carbs.

230/8

Mike D · #14 07-31-2007, 04:55 PM

Ryan,

Try 230/8's way first. He's got a lot more experience with the Zenith's than I have.

rgnprof · #15 08-01-2007, 09:04 AM

230/8,

So the primary throttle plates should be open just a crack? And, should I also disconnect the linkage at the front carb to the accelerator linkage? (BTW, I am thinking I have a problem with the whole linkage set-up - I have the bar type, not the rod, and I can't find specs, measurements etc. anywhere for this).

ryan