Zenith 36 VI 2

[welleyes]

We continue to have problems getting a reliable idle with 36 VI 2 carburettor. It is jetted as recommended but dies very readily at idling speed. When the engine is completely hot the problem ceases, but it takes a very very long time to get that hot. The first few miles necessitate juggling with the hand throttle or the starting device every time a junction, a roundabout or a traffic holdup looms ahead. Does anyone have any suggestions?

Stuart

PS Amals, Skinner Unions and Minnow Fishes seem so easy in comparison!

[jus]

Maybe a larger slow running jet is needed?
Not the same carb - but I've just had to fit a larger main jet to my S2a Land Rover's Zenith 36IV carb in order to get any life out of it. I had several 125 jets that came with refurb kits, and I just drilled one out to 150 or 1.5mm. The change seems to have woken the engine up. This pdf was quite handy for my situation.
https://zenithcarb.co.uk/zenseriesiv/?___store=zenith

[Raahauge]

The symptoms you describe are consistent with a worn throttle spindle, they can let in enough air to cause an idle problem.

[welleyes]

Thank you for your comments and suggestions. We had already considered the slow running jet, but not a worn spindle. We need the car for the next couple of weeks but will, after that, take off the carb for another look.

Mucking about with engines and sorting out problems used to be fun. It is less enjoyable when one is old; consequently, I do things less logically and carefully than I used to in the hope that faults will cure themselves. They never do, of course. Again, thanks.

Stuart

[chriswgawne]

There have been several comments in various posts (including this one) over the last few years about modern fuels containing ethylene needing carburettor main jets to be increased in size by typically 10 to 20% to allow the engine to run smoothly.
Is this actually the case or is it one of those tales like Aurelia juddering front brakes which are oft repeated but which I have never experienced in over 45 years of Aurelias with multiple vehicles?
Chris                   

[welleyes]

A few years ago, just out of idle curiosity,  I looked for more information on prewar and just postwar fuels with either ethanol or benzol added.  L G Callingham was the expert of the day and, concerning ethanol, he wrote, “Consumption owing to the low calorific value of the fuel, must necessarily be very high compared with petrol. While the correct air-fuel ratio by weight for petrol is 14:1 to 15:1, it is but 7:1 to 9:1 for alcohol - jet sizes have at least to be doubled with fuels containing 70% or more alcohol … ”  With E5 or E10, presumably one might predict a proportionately smaller increase.  Callingham warned that ethanol had a scouring effect on fuel lines and was a solvent on shellac varnish (as used on cork floats). He also warns of the problem of alcohols great affinity for water and  that it would probably “cause the components of the fuel to separate” He advises draining the fuel tank if the car is not to be used for several days and putting the fuel back in after filtering the water out with a chamois lined funnel!

Warnings about benzole (or benzol) went on into the sixties. It was considered inadvisable to use petrol with benzol added if you rode or drove a two stroke as it would damage the crankcase seals. In a postwar dealer's hints on running prewar Morgan three wheelers, it is advised not to hold high revs for more than a short time if fuel contained benzole. It was possible to add benzole to ethylised petrol; in September 1935 Motor Sport warned that “In large proportions, say 50 per cent of the fuel, benzol mixtures tend to make the car run rather hot while alcohol has the opposite effect and also calls for larger jets.”

I don’t know if all that very old expertise helps, but it does seem to suggest that a small increase in jet size might be worth trying. I ought to own up to being a retired English teacher, so can claim no relevant technical knowledge. I also ought to say that prewar vee twin engines seem happy on E5 or E10, though many owners expect their vintage or PVT cars to dissolve if left for a few days with the feared fuel in the tank.

[davidwheeler]

My Fulvia definitely benefited from larger "slow running" jets.

[welleyes]

Does anyone running a Zenith 36 VI-2 know what jets they are running? Ours may not all be correct.

Thanks

Stuart