Zenith questions

[BD55]

Hi to all
I have decided to take the Zeniths on my C coupe off for a rebuild due to various leaks....

I have stripped the carbs down today and have a couple of question:

I first thought that the main leak I have is from the throttle body shaft (Left hand carb) but after reading all the threads on here and Registry, I am now doubting this. And as the leak is at the front of the carb (front of car) it's difficult to see where it originated, so the question I have is how much play in the shaft is acceptable? I have yet to do any tests but when the throttle is closed I can see daylight past the butterflies, the shaft moves slightly in all directions, front to back and 'around'

Also I have noticed that the main venturi's are sitting slightly proud of the carb body about 0.5mm and I can see daylight between the carb body and venturi, this is on both carbs, I'm guessing that is not normal.

Any help, advise or observations would be appreciated
Cheers
Simon

[Ashley James]

I've got a couple of spare Zeniths here, so I'll have a look and report back. Funny thing is that Rich (son) has a forties Silver Wraith in his workshop at the moment with a very similar looking Zenith on it.

[BD55]

Thank you Ashley
I have since done a test on the throttle bodies as per Ron La Dow's instructions. Attaching the throttle bodies to the carb bodies and with the butterflies held closed, filled the venturies with water and timed how long it took to leak out from the top of the throttle body casting to top of closed butterfly takes between 35 and 40 seconds, not brilliant but according to Ron acceptable.....

Regarding the venturi's I think I will make a tool to take them out, clean everything and attempt to refit them flush with the body.
Hard to see in this pic but it is sitting proud....

[Ashley James]

The trouble with worn butterflies is that tickover is all over the place. I'm not used to Zeniths compared to SUs, but sometimes new spindles are enough. Can you get some. If the bodies have to be rebushed, I'd get someone very good to do it or not bother.

[marc500]

Every old car I've had has had a warped carb top from overtightening. Worth flattening 'em down while apart... I use a piece of glass laid flat on the floor for a totally flat surface to work from, then work through some grades of emery paper, laying the paper on the glass and rubbing the carb top and then carb body on the paper. A circular motion seems best and you'll soon see where the high/low spots spots are. Keep going until both surfaces are flat. That made my zeniths a bit less leaky!

[BD55]

Thanks for the replies. Marc I have checked for flatness on all the mating surfaces and they are pretty good, but will tidy them up when I reassemble....
I'm going to try to adjust the butterflies, if that doesn't work I will look into getting the throttle bodies refurbished and will go from there.
Thanks again.
Simon

[Ashley James]

There's a very clever chap in Cirencester who did my SUs for the Healey, he's ex Ashton Keynes, so I'll dig out his contact details if you decide to rebush. It is worth it.

[roy mawbey]

Simon,

A long time ago I was convinced the petrol leak on one of my Zeniths was from the throttle body shaft. I thought for sure that was the problem. Not so in my case. I eventually found the jet cover with the 10mm bolt was the culprit. The gasket had failed at the bottom of the cover. Petrol then leaked down to the bottom of the carb and along to where the shaft is.

I tell you, I wiped the carb so many times trying to see the leak but because it was at the bottom of the square cover you could not see it. Worth just checking that, as my Zeniths have over 130 K on them and the shafts so far touch wood seem fine and have never been changed just serviced by me.

Roy

[BD55]

Thanks Roy.
I am beginning to think the same thing, the seal on the LH carb was split and I also found that one of the jets was not fully tightened. The carbs are now fully stripped down and I have rebuild kits so planning to try them with the throttle bodies as they are.

Ashley, thanks that may be useful. If I still have problems after I try the above I will contact you.

[Ashley James]

Throttle spindles don't cause leaks, but they do make tickover difficult to adjust and speed vary all over the place. Cars run far better with no wear.

[neilbardsley]

Unfortunately Charlie has just passed away but his last book may help you

http://forum.porsche356registry.org/vie ... 19&t=43264

[BD55]

Thanks Neil that could be useful, very sad news about Charlie.

[Ashley James]

Funnily enough there's and early Silver Wraith in the workshop with a Zenith on it which I know is almost a Cadillac carburettor, but now I can see it's almost a Porsche too. It's beautifully made.

[mycar]

When you have the carbs back together and before you fit them back onto the engine you could try this.



Tracing the source of the leaks in a Zenith ndix carburetor can be tricky. Modern unleaded fuel is far more volatile than the 4* of old and will migrate like mad around the carb body making it appear that a leak does spring from one spot when in fact it may actually be springing from another spot entirely.

You will need to assemble your own test rig, I use 8mm clear tube, a spare banjo, a fuel tap to stem the flow when necessary and a white spirit/turps bottle with the bottom cut off as a reservoir. This sort of fuel tap is what I use.



You will need to use unleaded fuel and not white spirit so please take the precautions necessary when open handling highly flammable liquids.

Tip:- latex gloves last less than one minute when handling petrol.

Remove the throttle body from the bottom of the carb, fuel leaks do not originate here, and set the carb level over a piece of paper on a couple of small pieces of wood in a metal roasting tray from the Asda. Attach your fuel rig banjo to the carb and fill the reservoir with about 1/2 pint of fuel.

As the float bowls fill watch your carburetor closely. Zeniths can leak on the inside..... down into the cylinders... and outside..... all over the tinware, engine compartment and ground.

Some leaks are obvious....



Others a little more confusing....



Sometimes a carburetor will oblige by leaking almost straight away..... othertimes it may take 20 hours before the fuel will wick past a needle valve seat and down the throat.

That's the one that hydro locks your engine.

Diagnosing the symptoms..... that's where it's at.

[BD55]

Mike
Thanks for taking the time to post, I've been reading your posts on the Registry and here, very helpful indeed.
Just gathering all the parts and equipment I need to carry out the tests...looks like I need a float level gauge of some sort to set the float valves. And I snapped a accelerator pump linkage, so I will have to make another.

So were you fully successful in the end?