2800cs Zeniths: Solution sought in the UK

dj_efk

dj_efk

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Hi all, it’s been a while!

My Coupe’s engine has been completely rebuilt and the time came to rebuild the original Zeniths, so they were stripped down to their component parts, cleaned up and gone right through with all parts from the more comprehensive of the two types of rebuild kits replaced with new.

During this process, it was noted that there was some minor pitting and scoring in the venturi but it was deemed minor enough to continue, this may or may not be relevant to the issue I know have:

The workshop performing the work cannot get the carbs to supply the correct amount of fuel, they have spent many hours checking and re-checking their work and are at a loss as to what the issue is. They are now suggesting we swap them out with a Weber conversion kit, which I am loathed to do, especially as I cannot recall ever having heard of such an issue (and that the carbs are a poor design, as they suggest - and cannot be made to work). So I’m running up a SOS here for advice.

In terms of credentials, the workshop is a well-known (in classic car racing circles) tuning firm who specialise in carb rebuilds and tuning - however they are not experienced with this exact type of carb: So I consulted a second carb specialist who is, based again here in the UK and came recommended- They said the same: That these carbs aren’t worth bothering with and can be impossible to setup even if following the official Zenith manual (which Jesus sent me some years ago).

I am astounded that I haven’t heard of such issues previously, hence I suspect I haven’t found the correct specialist to set the carbs up yet!

I suspect the problem could be warped mating surfaces on the carb bodies, but I’m not not confident I have the right people for the job who can work through the issue to my satisfaction - despite my having sent them the manual, I doubt they have read it properly for example - Who can recommend someone I could speak to in the UK to get this resolved?

Thanks
 
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I also have never heard that these carbs are 'unrestorable'.
Warped mating surfaces on the top 'hat' does occur (I had one that showed it) and it would cause false air being drawn in. If disassembled, then lay the parts on a glass surface and check for gap. Or use the blue paste to check clearance. 'Plasticauge'i think it's called.

You could check with BCPP in Gramsbergen, the Netherlands. They do know these carbs, and have been used by a few of the Dutch E9 club members with good results. We even had a tour of their facilities a few years back with the club, and they even had 2 sets of E9 carbs going through their repair process.
If I remember well, it was a 1000 euro's for a complete rebuild, and then additional costs if you want them to be installed on your car and dialed in on a rolling road.
Not easy to drive your car there, but you could talk to them, and explain the problem. a phone call isn't that expensive. They are internally oriented so I bet you they speak English.
 
I have done lots of these carbs and there are some tricks to them The different sections are prone to warping so I use 400 wet and dry paper on a piece of glass to sand them flat This is critical as vacuum is brought up from the base late through a couple of sections Also, watch the kits, some of the gaskets fit but only the right ones works for your carb, check the small holes in the gaskets that allow air passages to go between the sections The one gasket that goes between the base and first section is like a figure 8 ( a bit anyways ) there are good ones and bad ones, the good ones are usually the older bakelite material they work the best There is a small o ring in this gasket DO NOT LOSE IT this one of the biggest problem replace them if they are too flattened Really clean out all air passages follow the blue manual as far as setting it up Also make sure that the secondary throttle plate stop is set exactly correct good luck with your carbs check out an old pust of mine called " carb candy " Thanks, Rick
 
dj_efk said:
Thanks for your detailed input @eriknetherlands - I’m looking for a specialist based here who I could take my carbs / car to, rather than just a phone call however.
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I see the issue, it would be favorable if you learn about a shop nearby.
If you don't succeed locally, then just keep 'em in mind; sending your carbs there to check their internals/ working order could work if your phone call gives you confidence....
 
Thank you both.

I would be interested in any UK-based members with solid recommendations as to who I (well, the car) could go to. Also any further speculation as to the cause of the carbs not drawing sufficient / a stable amount of fuel are also welcome. The warpage theory is just one I suspect it could be based on the symptoms / common issues I’ve read about here.

@stphers the car is 100-odd miles from me in a workshop who are out of ideas other than replace with a Weber DGAV kit - plus having just relocated from Asia I do not have time, I just need to solve the issue so that the car can be auctioned once all done and set up.

Thanks all
 
What Rick said! Also when assembling the bodies wait a day or so and retighten the screws to allow for gasket compression. Same when mounting to the manifolds.

stphers said:
I have done lots of these carbs and there are some tricks to them The different sections are prone to warping so I use 400 wet and dry paper on a piece of glass to sand them flat This is critical as vacuum is brought up from the base late through a couple of sections Also, watch the kits, some of the gaskets fit but only the right ones works for your carb, check the small holes in the gaskets that allow air passages to go between the sections The one gasket that goes between the base and first section is like a figure 8 ( a bit anyways ) there are good ones and bad ones, the good ones are usually the older bakelite material they work the best There is a small o ring in this gasket DO NOT LOSE IT this one of the biggest problem replace them if they are too flattened Really clean out all air passages follow the blue manual as far as setting it up Also make sure that the secondary throttle plate stop is set exactly correct good luck with your carbs check out an old pust of mine called " carb candy " Thanks, Rick
Click to expand...
 
So if I hear you all correctly, the only things it is likely to be are:

1) Body warping, causing vacuum leaks
2) Insufficiently tightened fixings holding the carbs together / to the manifold (same result - leaks).
3) Poor quality gaskets in the rebuild kits

Are there ANY other likely possible causes that anyone can think of? I am loathed to replace with a Weber kit.
 
1) Body warping, causing vacuum leaks
i found one case of warped top pieces, just the thin top piece, the one that holds the top butterfly
easy to check just put a ruler against it

2) Insufficiently tightened fixings holding the carbs together / to the manifold (same result - leaks).
rare to see this, and easy to check and fix

3) Poor quality gaskets in the rebuild kits
meh, yes, there is real crap out there, but,...

i would say:
4) incorrect table settings

or 5) horrendously mistaken assembly

i agree shops dislike these carbs, and they do not even try to understand and follow the rules

they are mega easy to work with, but you must follow the rules
 
Hello Jesus, I wondered when (not if) you would join this thread as I know it’s a subject dear to your heart!

OK so I believe I’ve got my issue identified as lack of experience combined with one or more of the above points 1-3.

Has anyone else ever come across a set that continued to give problems such as I’ve described even after all of the above had been checked / corrected? Discounting throttle butterfly shaft wear too as that has been checked.

Thanks
 
Can't tell from your post if they won't idle...or won't run. Look down all 4 barrels at idle and see where there's visible gas and go from there. Make sure the secondaries are closed. Where the visible gas is is where the air/fuel leak is. The kits are mostly horrible. The gaskets are poor or incorrect, the needle/seats leak when new, and the carbs are a known PITA to redo and tune. Regardless of what the wizards say. At $100/hr for tuning with questionable results, you have to balance the cost of the Webers against tuning time . Most buyers will see the Webers as value-added, especially if the original Zeniths accompany the car in a box.
 
The car starts, runs and idles - it just doesn’t run particularly well and is impossible to tune.

I take your point re: Weber cost vs. Tuning time. I see there is a choice of two Weber kits and will start a thread on this in case it becomes necessary to go that way, however for now I’ve spent a load on getting the setup I have restored and rebuilt, so knowing that the original setup SHOULD be repairable, I’d like to exhaust this road first.
 
Are you totally sure it is a carb / air issue?
Fuel pump, fuel itself
Distributor
Coil
Spark plug leads.
Timing, both ignition and valve.
 
I’ve had an e3 with dual Zeniths. I say to adjust, and ran just fine for years. Seems to me the most essential and first step to trouble shooting any carb issue is to collect AFR data over a range of operating conditions so you know if the problem is in the idle/main/secondary or accel circuit.

My E9 was running poorly when I bought it. The PO said two expert shops had Tried to adjust the carbs, to no avail. Neither of those experts had bothered to gather Basic AFR vs throttle position vs rpm data. I did, which enabled a hack like me to find the specific problem in under 1 hour. The fix is just $45 worth of parts and a few more hours of labor.

I assume the expert shops you have employed has done the simple check I mentioned, and their issue is that of not knowing what carb changes to make. If so, ask them to share with you that diagnostic. Take that data (assuming it is accurate), and to someone familiar with the Zenith carbs. Thats should get you quickly to a diagnosis of specific faults and specific fixes.
 
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Cornishman said:
Are you totally sure it is a carb / air issue?
Fuel pump, fuel itself
Distributor
Coil
Spark plug leads.
Timing, both ignition and valve.
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sounds like sensible advice to go through the whole process, but i assume that the car has been recently recently restored and serviced

in any case the most classic car experts can sometimes be perfectly wrong (i experienced this too with the “best expert carb man in the area”, he set up iddle by touching the central screw that is only intended to be used to rise up rpms while synchro process)

yes, first is valve gaps at 0,25mm
then distributor, points gap at 0,40mm
then go for ignition setting with an strobo lamp, and check 22º BTDC, or the ball in the mark at 1700rpms advance port capped
and finally carburation at 900 and 1700, and if possible 3000rpms using flow meters and a gas meter to set correct mixture at iddle

first of all the table settings for the zeniths, the three of them

you can not miss a point, or take nothing for granted
all in all is a simple procedure but very laborious
 
bfeng said:
I’ve had an e3 with dual Zeniths. I say to adjust, and ran just fine for years. Seems to me the most essential and first step to trouble shooting any carb issue is to collect AFR data over a range of operating conditions so you know if the problem is in the idle/main/secondary or accel circuit.

My E9 was running poorly when I bought it. The PO said two expert shops had Tried to adjust the carbs, to no avail. Neither of those experts had bothered to gather Basic AFR vs throttle position vs rpm data. I did, which enabled a hack like me to find the specific problem in under 1 hour. The fix is just $45 worth of parts and a few more hours of labor.

I assume the expert shops you have employed has done the simple check I mentioned, and their issue is that of not knowing what carb changes to make. If so, ask them to share with you that diagnostic. Take that data (assuming it is accurate), and to someone familiar with the Zenith carbs. Thats should get you quickly to a diagnosis of specific faults and specific fixes.
Click to expand...


never saw a shop working with afr data in classic cars here
manual says nothing about using afr, or how to proceed with it
i will be lost if someone gives me that info

i can use %CO
 
The AFR reading is a derived (inferred) value based on measure residual oxygen content in the exhaust (using a common production oxygen sensor, typically Bosch).

You would not be lost. You and I know that 14.7 is stochiometeic, leaner is hotter richer is cooler and too far to either extreme is bad. A quick internet search will yield suggestions for reasonable AFR operating range for different driving. The rear is just the same in terms of jets, air correctors and throttle plates.

It is common to see these used in tuning classic cars here in the USA. They are cheap and have enough accuracy for even some racing applications. And most importantly, they help less good mechanics become better and good mechanics become even more good.

I am a strong proponent of using smarter/better tools to help us maintain our classic cars.

This discussion has gotten me interested I. Restoring my zenith carbs. It would be fun to get them working as new and them put them on display in my garage.
 
When I rebuilt my Zeniths I kept the original float needle valves, the replacements were unacceptable. The float can also get hung on the gasket if not trimmed. There is an old thread describing the procedure of covering the top cover vent hole to see if idle changes, if so there is a leak.
 
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