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Poor running with a zenith carburettor

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Simon Hyslop
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Joined: Wed May 04, 2016 3:30 pm

Poor running with a zenith carburettor

Post by Simon Hyslop » Tue May 14, 2019 6:13 pm

I have been somewhat puzzled for a little while with poor running on two of the fleet.They aren't, on the face of it, that similar - the LD10 and my wife's Triumph Herald 13/60. Both were displaying similar symptoms, running ok for a while then refusing to rev up or dying when the accelerator was opened. Petrol at the pump and petrol at the pipe to the carburettor both suggested an electrical problem due to a failing warming up component and the Triumph has had three coils, condensers, rotor arms, points etc. However, the trouble has proved to be none of these.

The common feature with the LD10 and the Herald is that their carburettors share the same float valve, a 1.5 (number on the side) valve Zenith used back to at least 1932 as I have several examples off Austin 10 carbs back to then. On closer examination they are all showing the same symptoms, namely a stickiness in their movement and two new ones (part no. B19052) are on their way from Burlen Fuel Systems. I had one new one in the box of carb bits and today have completed the first trouble free journey in the Herald for quite some time. I am hoping that the LD10 will respond in a similar fashion, the same routine having been gone through with its electrics.

I should have diagnosed it sooner but everything else I have at present is fitted with SU carbs and the new Viton tipped valves from Burlen. These seem to have pretty much eliminated needle valve troubles from the SUs and I had sort of forgotten what bother they can give. Around 1970 I remember a journey with my mother and father from Dumfries to Annan where we stopped every couple of miles for the float chamber to be given a dunt on its side until we reached the BMC garage and a new one was bought.

I thought this might be of use at some future time to a similarly puzzled person who wished to make some progress on the road.

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Re: Poor running with a zenith carburettor

Post by John-B » Tue May 14, 2019 8:19 pm

Interesting. I read the first few lines and thought "dirty fuel" as you probably fill up both cars at the same petrol station. Do you remember the Tesco fiasco a few years ago when hundreds of people got contaminated fuel?

Simon Hyslop
Posts: 261
Joined: Wed May 04, 2016 3:30 pm

Re: Poor running with a zenith carburettor

Post by Simon Hyslop » Wed May 15, 2019 12:31 am

Old fuel, yes, dirty -no. I drained the tank on the LD10 and there wasn't a speck in the eight gallons. The petrol comes in dribs and drabs from various sources. Having examined about half a dozen other old Zenith valves, I have to conclude that there is something about them which is prone to either some form of corrosion or deposit, probably not surprising considering their age. I looked tonight at the valve on my 1947 Rover, a Solex one, and it was absolutely as new with the same petrol sources so the SU and Solex valves seem relatively unaffected.

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Re: Poor running with a zenith carburettor

Post by classiclife » Wed May 15, 2019 9:29 am

Hello Simon,

Thanks for posting this and very interesting topic.

I run a Triumph Vitesse Mk2 along side the Daimler; being a member of the TSSC I have never heard your problem previously reported via their Forum or other members I have spoken with over the years - hence the interest in your topic.

You mention corrosion deposit and I guess probably some very minor gumming.

I would be interested to know what and whose fuel you use.

Of note, old modern fuel does degrade very quickly left over a period of time and the by-product of this degrading is highly likely to have an adverse reaction to the carb(s) - fuel does not have to be dirty to be problematic.

Out of interest do you use any additive such as Redex or especially Flexolite Ethanolmate - if not this may be of use and specifically the Ethanolmate.

One of my other clubs sells this extensively and the feedback has been very positive; especially with fuel issues and carb tarnishing.

If you think it may be of assistance and worth trying, I will be happy to send you a bottle at wholesale cost + postage, which works out at £12 in total. Certainly far cheaper than buying direct from the company as a retail customer !!

Purely a suggestion.

Best wishes.

1968 Daimler V8-250 Saloon
DLOC East Sussex Area Representative.

Southern Classics Society Events Co-ordinator.

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