Trouble in Zenith-land, now wot?

Honolulu

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Longish and sad.

Synched the carbs last weekend using my UniSyn and a homemade adaptor. Idle and about 2000 rpm okay. Tried out a bit of 1/8 inch tubing connected to the vacuum ports, with some ATF. Noticed the rear carb secondary drawing quite a bit of air at 2500, and that the synch previously set goes all to heck around 2500.

The car has been running hideous rich, exhaust reeks, so something's wrong.

I have been researching Benz Kjet (as used in BMW 320i also) and knew various 70's Benzes also used Zeniths. I came on the comment that the Zenith castings warp if tightened too much. I suspect that's what I've done. I have a "spare" pair of carbs from a 2800 sedan that have warped castings.

Now what to do?

1. Disassemble, try to straighten/sand the castings flat, then reinstall? Dunno if the warp can be ground out or if it's worth it.

2. Use that 528i Ljet head and injection system I've had sitting around for five-plus years? Injectors may be gummed up.

3. Strip the '87 735i which has a cracked windshield, a bit of rust, and failed AC, that I can't sell now and would be hard pressed to repair and break even on? Nice car when I drive it but no registration or insurance on it nowadays. Transfer injected motor and auto trans? Maybe better to keep the 5-speed and speedo connected.

4. Suck it in and buy 32/36s from somewhere, or if lucky, 38/38s, and linkage? I surely distrust used 32/36s since they wear badly at the throttle shafts - won't hold steady idle then. New seem about $250 per.

How say the multitude?
Anyone got some straight carbies laying about?
 
Decisions decisions: miscellaneous ramblings

If I were in your shoes or flip flops, I would take the course of least resistance.

If I understand your post, you suspect only one of the carbs to be worthy of davy jone's locker. If you know that to be the case, you have nothing to lose but time if you take it apart. I have not dealt with Zeniths in quite a while, but for easy warpage, try the Solex didta 2bbl downdrafts. Some warpage is not that difficult to remedy. I seem to remember having a leak on a Zenith below the throttle shaft where the bottom mates with the phenolic resin spacer/gasket. Use of a fine file took care of the situation. Internal warpage - due to heat or poor casting is practically hopeless. I used to know a few old timers/pseudo watchmakers who would solder orifices and re drill them, but at least they claimed to know what they were doing.

If you look at one of the expanded diagrams of the Zenith, you may note there are a number of tiny "o" rings that seat between many parts - including dashpots for the secondary. I would not be surprised if, after so many eons, these little rubber donuts have ossified. But I doubt all of that richness could be attributed to leaky o rings. On the other hand, there is a first time for everything.

Another consideration is crap in the carb. Despite all of the filters in the world, I used to find all kinds of debris in my fuel bowls. It may be that a liberal use of gumout or a dunk tank followed by compressed air may be all that is required. Considering your climate, I would expect the carbs develops a fair bit of internal corrosion. Pot metal corrodes doesn't it? At least mine used to shed a nice bit of white-ish oxide. If you have few problems though 2000 rpm, sounds like either a progression issue, the secondary is goofy or - the accelerator pump is leaking (hence the richness). If there were vacuum leaks, one might expect the mixture to be ultra lean.

Respecting the use of a carb synchronizer, the device you describe and/or a vacuum gauge can be useful, but I am more inclined to use a length of fuel line and try to match pitch with my ear.

I will not suggest getting your rotors turned, although making sure your brakes are in order is always prudent when driving near volcanoes or grass skirts. ;)

To compound the equation, have you considered getting yourself a spare Zenith?

Good luck and please post your ultimate successful outcome!
 
And if mptivated to re-build Zeniths--the large re-build kit

for the Zenith INAT 35/40 Is available from:

www.royze.com 800-421-2011 Garden Grove, CA at around $45-50 per kit last time I checked.
 
I am more inclined to use a length of fuel line and try to match pitch with my ea
Spoken like a true multi-carb master. IMHO this is definitely the best way to sync the carbs. I used to play with meters, vac tubes, and the like but I met a master Alpha Romeo mechanic who taught me the hose technique with side draft Webers and I have been a hose-in-ear man ever since!

I once had the problem you described with my E3. I rather doubt that anything is warped or cracked. The "crap in the carbs" theory is worthy of exploration. My problem stemmed from high fuel pressure (prior electronic pump conversion) and bad float valves (basically my float level was simply too high). Have you looked at your float level? One of the telltale signs is that when looking straight down the barrels of the carbs at idle you may see fuel dripping from the venturis (primary and/or secondary). If you do you can pop the carb tops of pretty easily and have a look inside (where you may also be able to see junk and even water). To fix my problem, rather than actually buying a new needle valve (being a starving student), I simply bent the float a bit until it maintained the proper level; this took a few iterations. This may actually be the proper procedure too as I don't recall an adjustment screw. Later on I added a fuel regulator.

Another quick thing worth doing is to pull your plugs. If you have a "bad" carb then the you should see 1-2-3 or 4-5-6, but not both banks, carbon fouled. If they are all fouled it is not one bad carb and two simultaneously failing carbs (cracks, warps, etc) is very unlikely).

This winder I'm planning to swap out my Weber 32/36's and put Zeniths back on. I have purchased two pair of used Zeniths and rebuilt kits figuring I can make at least one good pair. If you find yourself in need of a specific carb part send me a PM and we can arrange a deal... mac nuts, kona coffee, pictures of girls in grass skirts, etc. for various carb parts. :D
 
Grass skirts and coconuts

Thoughts of Grass skirts and coconuts caused me to revisit this post. Now all I can think of is crab cakes.

THe more I think about it, a stuck float , a leaky float, or a maladjusted float will cause flooding and/or the very rich running you seem to be complaining about. Why it wouldn't affect the idle, I am not sure. But before you do the hula to the carbs and sacrifice one or both to the Kilauea, pull the top of the offending carb and examine the float drop. I am pretty certain the float specs are available via Haynes or the Blue books and bending the adjusting tang requires two specialized tools: thumb and index finger or needle nose pliers.

BTW, not that anyone cares, but I am partial to the console I saw in someone's 02 that was wearing Koa wood. Parked at industrial park near Pearl. Very nice. Damn, now I can't stop thinking about Jack Lord's hair.

Good luck.
 
Thanks for the info/advise...

...more details of travails: One of the carbs starts to whistle loudly, somewhere around 1500 rpm. I’ve been into both carbs, though it was some time ago, and the innards were pretty clean. There was only a tiny bit of dust when the bowls dried out, and the internals (having been filled with gas) were not corroded. External leaks result in reddish gas stains, not white corrosion. I’ve not seen white corrosion on either of these carbies.

Since the car runs way rich, I don’t believe it’s a vacuum leak causing the problem.

I tried the hose to the ear, it wasn’t working for me. I know the manometer is accurate, I believe the Uni-Syn is accurate. I once borrowed the factory synchronizer, but it does not work at other than idle speed. Extremely sensitive, though. I am confident of both my Uni and tubing manometer. My approach was per the book; I did not use the screw on the linkage near the front carb to hold 2500 rpm though that’s what it’s there for as far as I can tell.

As noted I have not one but two “spare” Zeniths from a 2800. I think the only difference is in the main jets.

Bad float or needle valve is worth investigating. My 10th grade daughter is in Chemistry, and they have an analytical balance. I can trim the floats to a whisker off a gnat’s behind, if I want to. Believe this is my next step - pull the tops and check the floats for leaks and needles for crap.

All six plugs looked much the same, or not different enough to point to one carb or other. They were not black and greasy though they were darker than I would like to have seen. This teaches nothing, I knew it was running rich. Could I have two bent carbs? Time and elbow grease will be spent before the answer is known. I can also visit a retired master bimmerman who ran the local dealer’s shop for a bit. Just have to be sure to bring the correct brand of this-n-that...
 
If my memory serves well the floats are a composite material and they can't leak. The main reason for a change in float level is a worn (or moderately failing) needle valve.

The simplest way to detect a high float level is to look for fuel droplets coming from the venturis at idle.

Since both banks of plugs are about the same it really doesn't seem like a carb problem; carb will almost always fail one at a time. The only common fuel sourcing problem I can think of would be fuel pressure that it too high. Are you running the original mechanical pump?

I'm starting to think you may have a fuel burn problem rather than oversupply. Your issue with erratic air flow at 2500 is suspicious. This could be almost anything. Valve gap, weak coil, bad cap / rotor, dwell, timing, or even cam timing (mine was off 1 tooth when I got car). I also had a partially shorted condenser on the distributor. It gave all the classic symptom of carb problems even though the carbs were fine.
 
Another possibility is that the carb top cover is warped. This can be checked by removing the cover and using a GOOD straight edge and checking for daylight. If it is warped the venturies can suck air and fuel directly from the float chamber.
The way it gets warped is by overtightening the nuts that hold down the air cleaner. Because they are large nylon insert nuts (you don't want them coming loose and going down the venturi), you can't feel when the nut is getting snug. I always tightened them very slowly while jiggling the air cleaner up and down. When the free play ceases, STOP.
The top cover surface can be dressed flat with a large flat file.
 
This is just a long shot, but.......two years ago my coupe would not accelerate, it stumbled with any kind of load, but it idled fine. My mechanic could not figure it out. He took the rear zenith apart twice, it was not drawing very much vacuum. Out of shear luck, when the carb was apart, he found a small piece of metal in the bowl. When the carbs are made, there are two vertical tubes that are siameezed together when cast, then a small opening is drilled between the two at the very top to connect them. They then close the entry hole with a small metal swage, not much bigger than a very thick pencil lead. He fastened it back in place and the problem was gone. To think that if he had turned the bowl over and not noticed this tiny piece of metal that could have dropped to the floor, you get the picture.
 
Then came the flood

My 2800 has been sitting for several months waiting for it's turn in the garage. I just got two new Pebra keys cut by keys4classics.com in OZ and wanted to try them out. I started up the car, which as is usual for it after sitting, took a fair amount of cranking to get fuel to the carbs. Usually it starts right up after the first cough, but this time it took several more tries. The idle was lower than I remember.
She smelled a bit gassy and I was thinking how much cleaner cars with catalytic converters are. I let it idle and opened the hood to survey the scenery. As I went around to the right side I was greeted by gas pouring out of the air cleaner intake at a steady rate. I raced to the open door and shut off the ignition. I'm thankful I put on new spark wires when I got the car, or things might have gotten quite hot.
Pulling the cover from the air cleaner, it's obvious the front carb was where the action was. Gas was pooled in the air cleaner, the new gaskets below keeping it from running down the outside of the carbs.
I had not read about the dangers of over tightening the nut on top of the carb until after I had reinstalled the carbs after cleaning them and putting in new gaskets. I suppose it's possible that the top as warped and thus the leak was from the float bowl. Odd that it wasn't flooding the engine since it was flowing freely.

I'm letting the gas evaporate and I'll investigate further in a bit.
Any other suggestions?
I'll have to look and see if the OEM nuts are still available too.

Ian

Video of the moment of realization.
https://youtu.be/ApjfLwwS1ls
 

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FWIW Might be worth calling Mike at Peirce Manifolds in Gilroy, CA... Big time weber expert but a carb is a carb.....Also they have a series of videos on youtube that might be worth watching.. again for the weber DGV series but I learned some new things from watching. (like the cost of getting my old carbs right would be money wasted in the long run. https://www.youtube.com/watch?v=A44-xG3pKlY

I put on some 38/38s a couple of weeks ago and wow what a difference from the tired 32/36s that were on the car.... I was able to just get by with just the carbs since the 32/36s use the same linkage...$239 each on ebay plus $16 for shipping. Pierce sells them on ebay here http://www.ebay.com/itm/361513296752?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT
 
Sounds like your float needle valve either is hanging up or has dirt in it preventing it from closing properly
 
Yes, maybe, perhaps.

Sounds like your float needle valve either is hanging up or has dirt in it preventing it from closing properly

I'm hoping it's the needle valve. I kept the originals installed when I opened and cleaned the carbs, the ones in the kit seemed inferior.

Starcruiser, Thanks for the links, I haven't seen that information on the Zeniths before.

Ian
 
Well

you opened up the carb to clean and the gaskets were inferior .IIRC.

What that means is that the gasket over the float is probably slightly larger not letting the float come down. The tolerance is close even on a proper gasket.

Just pop the top and trim the gasket is my recommendation. Easy fix to prevent happening again.

You could take the vent off and force it gently down. But that's a temp fix.
 
you opened up the carb to clean and the gaskets were inferior .IIRC.

What that means is that the gasket over the float is probably slightly larger not letting the float come down. The tolerance is close even on a proper gasket.

Just pop the top and trim the gasket is my recommendation. Easy fix to prevent happening again.

You could take the vent off and force it gently down. But that's a temp fix.

+1

i found this fault when this happened to me, i trimmed the gasket just like i do in this video.
http://youtu.be/EmGxdiCYYYI

this is a nine video collection of how to reassembly the carbs, number 2 and number 3 shows how to trim the gasket to avoid the floater get trapped

hope it helps
 
And there lies the answer, I hope

Excellent advice from the forum! Thanks to all for the input.

The leading suspect is a too large gasket hanging up the float. Spanish isn't one of the languages I even come close to fluency in, but DeQuincey's video made it quite clear where the issue might lie.

I'll get the top off the carbs in a bit to check it out but other projects have priority.

Ian

Zenith-carb-gasket-catching-bowl-float.jpg
 
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