Zenith Carburettors On Jupiter

[Mike Allfrey]

Coming on here is one of my New Year Resolutions - to join in more often.

I have installed a pair of Javelin Zenith carburettors in place of the Solex pair I fitted before. The reason for this action was, firstly, to try and fix a black exhaust smoke situation and, secondly, to sort of get back to original appearance. In addition, the coolant plumbing to the heated throttle bodies could be removed. All of this went quite well.

I opted for a pair of Javelin Zeniths just for the sake of having throttle levers that swing in a clockwise direction when viewed from the driver's seat. The 32 VMs that came originally with the car, have the levers swinging in the opposite direction and the Bowden cable (outer) has to push the throttles open, in the same way as a Standard 10. With our State (Victoria) being obsessed with nannyism and the consequent lower speed limits, there is not a great deal of need for performance any more. I say, bring back the man with his red flag!
I purchased a second hand set and they, along with their new cable set up fitted OK. The petrol tank was drained and some fresh BP was poured in. I also installed a Petrol King Fuel Saver pressure regulator, of Italian make.

Then, on trying to start the engine, it was found to be very difficult to start. Once started and carefully warmed up, it was impossible to get the engine to idle below 2,000 engine rpm. I then screwed in the LHS throttle stop by two-and-a-half turns, gradually until it would run long enough for me to have a look at what was happening. Another point, when opening the throttles to keep the engine from stalling, there were shrill whistle sounds at the air intakes. Quite alarming!

Once it was running, I decided to remove the oil filler cap. This was interesting, there was sufficient vacuum to hold the unscrewed cap in place and it took a fair bit of lifting away. Placing my finger over the breather hole, there was a vacuum there and, with my finger in place, there was not much change to the way the engine was running.

Tomorrow I will be having a look at the felts in the tappet chests, and fitting a new AC breathe valve that sits in it box on a shelf somewhere in my workshop. I know that bunged up felts can affect the mechanical pump on a Javelin, but that is usually fuel starvation.

Another interesting point, after switching off the engine, petrol drips from the throttle shafts for quite a while. Makes me wonder if the pressure regulator causes that.

Will advise what, if anything develops tomorrow.

On another topic, my Technical Notes Series are now up to Number 38, with the latest being about securing a loose starter ring-gear. That will be E-mailed after proof reading.

All the best,

Mike A.

[Keith Clements]

Thanks Mike, good to see you back , and what a great NYR.

Seems like you have a plethora of problems which often beset the Zenith. The drippy carb body is often caused by the needle valve, but could be a hole in the float, missing spacer washer or the high pressure. 1 metre of plastic tubing is the best way to test. If it happens when the engine is running, suspect a poorly sealing gasket between float chamber and body. I have found many distorted chambers/bodies which need flattening with fine file or grinding paste. It can be a pain to remove the rivets holding the gasket in as it is difficult getting a grip on their dome head to twist anti-clockwise.

Always a good idea to use a short length of 15mm tube to listen around the head/carb body interface for hissing noises. Once again distortion of the faces may need to be rectified. A carb is easily distorted when dropped or poorly stored. Also check under the oil filter for a hissing noise. Once I found the pipe had worn away where it touched the block.

Breather valves can rust up as water condensate likes that area.

[Mike Allfrey]

Sorry to have been away for a while now. Been bogged down repairing the radiator and water pump on my Rover P6B (V-8). Usual stuff, someone really bodged the radiator's core and the water pump took some detaching from the crankcase. Just like the Javelin/Jupiter, bolts break through into the water jacket to rear of front timing cover. However, doing the job myself, I found that Loctite 243 is a suitable thread locker and sealant which could apply to the Jowett engine too!

The carburettors will be taken to have their throttle spindles renewed and the housings bushed and straightened to bring matters back to original. I forgot to mention that my Jupiter will be running Javelin spec. carburettors from now on.

I will advise progress.

Mike A.

[Mike Allfrey]

Further to this saga.
The engine is running nicely now, but it took a great amount of work to get it that way. In addition to drips of petrol, I also experienced a total blockage in the pipe from the tank to the pump.
Then the Scorcher coil (China), horizontally mounted, leaked some of its cooling oil into the high tension lead's rubber boot. The boot did not leak, but was large enough to accommodate a fair volume of oil. Thus the coil primary winding inside overheated locally and the result was no more go. All fixed now with a Bosch coil, made in Brazil.
Still requires a fair amount of cranking after standing idle for a week or more. but once run for a spell, it starts instantly every time.
Regards,
Mike Allfrey.

[Forumadmin]

Mike. When your Zeniths are refurbished do you fit new jets, throttle butterflies and needle valves?

[Mike Allfrey]

Thanks Keith,
The throttle shaft bores were machined ready for new spindles in new bushes. New butterfly plates were made and very carefully set to match the drilling for the vacuum pipe to the distributor. Also, the choke butterfly spindles were reset in new bushes. Reference the jets, I cannot remember at present, but I have a tub in the workshop with all the parts that were replaced, so will confirm that tomorrow. I did get a very nice throttle return spring which is ideal.
Took my Jupiter to our local library yesterday, it was one of those days why we live down here!, and came out to a large group of interested people. I fielded questions for a fair amount of time.
Saw Michael Portillo on a railway journey in Scotland this evening. He spent a fair amount of time in Glasgow, but I didn't spot Drummond there!
Regards,
Mike A.

[Keith Clements]

Luckily here we can still get most parts including new butterflies. Jets however can be difficult to find. Last time I did a Zenith I found the new butterflies did not seat properly so I reverted to the old ones. Impressive you made new ones!

[Mike Allfrey]

Hello Keith,
My carburettors were overhauled by a carburettor specialist, close to Tullamarine airport a fair drive from here. They skim bored the throttle bodies, made new butterflies to suit and installed them into new spindles, which in turn were assembled in new bushes in the throttle bodies.
It is amazing how distorted the carburettor bodies can become, hence the refacing of the flanges and truing-up of the throttle body bores. It seems that every used Jowett part I now come involved with, has been mutilated by some previous visitor!
All the best,
Mike A.

[Forumadmin]

Yes they do distort. Even the floats may not work as the reservoir is distorted.