FS: Zenith 35/40 carburettors
- Thread starter IS3FIFTY
- Start date
What is the rectangular device on the side of the carbs? Mine does not have that item, just wondering, thanks.
Zenith - rectagular box?
Thermo electric starting valve? The part with the aluminum cover with four screws; unless I misunderstood.
The carbs have the newer choke/ diaphram caps.
I don't see the shutoff valves or holes blanked so possibly euro/ early with an upgrade on the caps.
The carbs were used on several models/ makes and the jets are all pretty close except for automatic cars.
Has anyone ever rejetted for modern fuels? It's not been a problem for me looking at the plugs. But with modern mixes with gasahol/ additives cars like Porsches can see an increase in HP by jetting up two sizes. ( More fuel/ better burn with modern fuels.)
Thermo electric starting valve? The part with the aluminum cover with four screws; unless I misunderstood.
The carbs have the newer choke/ diaphram caps.
I don't see the shutoff valves or holes blanked so possibly euro/ early with an upgrade on the caps.
The carbs were used on several models/ makes and the jets are all pretty close except for automatic cars.
Has anyone ever rejetted for modern fuels? It's not been a problem for me looking at the plugs. But with modern mixes with gasahol/ additives cars like Porsches can see an increase in HP by jetting up two sizes. ( More fuel/ better burn with modern fuels.)
IS3FIFTY
Well-Known Member
I think that 61porsche might be right... Or are these the shut off valves? They have the 20 ohms symbol stamped on them. I will check tonight and provide more details.
Carb ID
The idle shut off valves would be shown in the second photo. Round electric cylinder solenoid that screws into the base, below the fuel inlet fitting and towards the center, and angled. Don't see them. But a couple others have reported the same carb. early 2800s?
The 20 OHMS ( Different spec cars had a different resistor- in the bluebooks) marking is for a resistor under the cover which lifts a valve/ port opening and supplements the choke circuit in very cold conditions. It's likely that this part causes rough idles. If backfiring occurs ( too much advance/ loose chain, etc.), it goes here too and the small valve becomes dislodged. Easy fix though once you know that's what happened. The gasket on the banjo bolt can leak here also.
The carbs are good. But it's these little things that people talk about warped bodies/ plates that can cause similar conditions and misdiagnosis.
As the cars become more valuable and scarce, there will be a faction of owners/ buyers that want originality. Some here have converted back to Zeniths from Webers.
It's always great to have a spare set around when you need them!
The idle shut off valves would be shown in the second photo. Round electric cylinder solenoid that screws into the base, below the fuel inlet fitting and towards the center, and angled. Don't see them. But a couple others have reported the same carb. early 2800s?
The 20 OHMS ( Different spec cars had a different resistor- in the bluebooks) marking is for a resistor under the cover which lifts a valve/ port opening and supplements the choke circuit in very cold conditions. It's likely that this part causes rough idles. If backfiring occurs ( too much advance/ loose chain, etc.), it goes here too and the small valve becomes dislodged. Easy fix though once you know that's what happened. The gasket on the banjo bolt can leak here also.
The carbs are good. But it's these little things that people talk about warped bodies/ plates that can cause similar conditions and misdiagnosis.
As the cars become more valuable and scarce, there will be a faction of owners/ buyers that want originality. Some here have converted back to Zeniths from Webers.
It's always great to have a spare set around when you need them!
Thanks 61,
I have a spare set for my `73 for that very reason but none of them have that 20ohm box for the chokes. Perhaps on very early or very late cars?
I have a spare set for my `73 for that very reason but none of them have that 20ohm box for the chokes. Perhaps on very early or very late cars?
Answered my own question with RealOEM: introduced during `74 non-U.S. VIN production.
THERMO STARTING-VALVE
Fg -> 4300416 / 3.0 Cs
Fg -> 4320528 / 3.0 Csa
THERMO STARTING-VALVE
Fg -> 4300416 / 3.0 Cs
Fg -> 4320528 / 3.0 Csa
Carb ID
Wow! That's interesting. I just chaulked it up to dealers/ mechanics changing carbs over the years and not really paying attention.
Both my sets have the valves. 1 set definately came from a Baravia ( E3); but when I disassembled them, only one of the set had the jets for an auto trans. ( Idle air jet =100). Go figure!
Since then I've had to use a few parts chasing the sometimes elusive smooth idle on the set in the car and resisting just turning them up.
Wow! That's interesting. I just chaulked it up to dealers/ mechanics changing carbs over the years and not really paying attention.
Both my sets have the valves. 1 set definately came from a Baravia ( E3); but when I disassembled them, only one of the set had the jets for an auto trans. ( Idle air jet =100). Go figure!
Since then I've had to use a few parts chasing the sometimes elusive smooth idle on the set in the car and resisting just turning them up.
gjm
Member
I've been looking at a '72 CSA that's for sale here in the UK. Some rust :shock: ;-) but not so much that it's unacceptable (to me), seized brakes, and lumpy running because "the carbs are out of balance", according to the seller. Of course he could be right. Or one of the bodies may have warped. Or...
What is the most likely reason? I appreciate that it's not easy to tell without seeing/hearing the problem.
And, IS3FIFTY, would you consider shipping to the UK? I'm not quite ready to manufacture manifold adapters for alternative carbs, or fit a FI system just yet!
IS3FIFTY
Well-Known Member
It could well be. I can't talk to the warping being a common problem on E9s (but others on this board may have more details on this). However, I've heard that this is a frequent problem on early (65-on) Mercedes-Benz (they used the same Zenith carbs) because the carbs are sitting right on top of the exhaust manifold...
Well, I may have a solution for you. I have some visitors who are heading back to the UK next week... You'd just have to meet them at Heathrow :-D.
If this doesn't work I'd be glad to look at shipping options for you.
Carbs, Etc.
Sounds like you have a buyer!
E9's exhaust is on the opposite side, so warping from heat generally isn't an issue. Over/ uneven tightening is though.
A rough or lumpy idle can be many things, including intentional as in a camshaft change or worn parts non related such as motor mounts that have long since given up but look normal.
A quick check is to cover the small idle air bleed hole next to the top jets/ vent while running. What you're doing is seeing if the mixture changes and the engine does nothing, increases speed, or decreases speed and in this case smooths out. If it smooths out appreciably, air is getting in somewhere it shouldn't and the hunt begins. The average mechanic would spray carb cleaner on it and pronounce AHA, warped! as the Weber legend goes.
But the guy who takes his time usually finds it something else like the secondary vacumn diaphram, choke body gasket, cold start valve we're discussing earlier, or simply a linkage adjustment; all very close to one another and act just like worn throttle shafts and warped bodies/ plates.
Balance- easy check with a vacumn guage first; if you don't have a fancy motometer/ manometer handy. Plug it in to each manifold, in turn. Are they pretty even? Believe it or not you can tune pretty close to the best burn ( (fuel/air ratio) with a simple guage. Tune for the best vacumn on each bank/ carb, then do the small adjustments together ( at the same time like the manual.)
Good vacumn means healthy engine and better fuel economy. Mo power too!. Then go find the fancy meter and smile because you just outsmarted the factory.
Sounds like you have a buyer!
E9's exhaust is on the opposite side, so warping from heat generally isn't an issue. Over/ uneven tightening is though.
A rough or lumpy idle can be many things, including intentional as in a camshaft change or worn parts non related such as motor mounts that have long since given up but look normal.
A quick check is to cover the small idle air bleed hole next to the top jets/ vent while running. What you're doing is seeing if the mixture changes and the engine does nothing, increases speed, or decreases speed and in this case smooths out. If it smooths out appreciably, air is getting in somewhere it shouldn't and the hunt begins. The average mechanic would spray carb cleaner on it and pronounce AHA, warped! as the Weber legend goes.
But the guy who takes his time usually finds it something else like the secondary vacumn diaphram, choke body gasket, cold start valve we're discussing earlier, or simply a linkage adjustment; all very close to one another and act just like worn throttle shafts and warped bodies/ plates.
Balance- easy check with a vacumn guage first; if you don't have a fancy motometer/ manometer handy. Plug it in to each manifold, in turn. Are they pretty even? Believe it or not you can tune pretty close to the best burn ( (fuel/air ratio) with a simple guage. Tune for the best vacumn on each bank/ carb, then do the small adjustments together ( at the same time like the manual.)
Good vacumn means healthy engine and better fuel economy. Mo power too!. Then go find the fancy meter and smile because you just outsmarted the factory.
IS3FIFTY
Well-Known Member
So, I checked my BMW factory repair manual and it shows that the thermal starter valves were only available on US models 1969-74. So yours have to be non-US ones.
Other bits from the manual, this carb on the 2800CS/CSA used the 20 ohms thermal valve and on the 3.0CS/CSA it used a 13 +2 ohms thermal valve.
gjm
Member
I like that kind of shipping! A very good friend did something similar for me with 'some' parts for a Porsche 928, including a many-volume workshop manual. How he and his wife carried it all I don't know.
Heathrow is exactly the wrong side of London to me, and a near-400 mile round trip. In itself not a problem, but more difficult is that I will be in Turkey from Tuesday evening.
Where (roughly) in the UK do your visitors live? The transatlantic shipping is the expensive bit!
Thanks, to all for their insight.
Graham
Well, the parts book says those are `74 and on non-US parts which makes sense if it's for colder climates. The Blue Books weren't written for the U.S. market but for all markets. I have never noticed where they specify US vs. non-US but I could be wrong, I don't have them in front of me.
IS3FIFTY
Well-Known Member
gjm
Member
IS3FIFTY
Well-Known Member
Carbs are sold!
Thanks lip277. It was a pleasure dealing with you.
Thanks lip277. It was a pleasure dealing with you.