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Zenith updraft brass carb info needed.

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i am in the process of trying to get a 1913 Vulcan 20 HP (English) running properly. The engine and most of the anciliaries have been rebuilt but the carb is showing signs of running too lean .Back firing through the carb at mid to high revs and leaking a lot of fuel when turned off.

Digging through my memory, i understand the float level should be below the main jet to prevent fuel siphoning by 3mm.

I have struck a problem in that in the dim distant past ,someone has removed the washers under the needle seat so the float level is all over the place. But i have sneaking suspicion someone has sharpened the needle to remove a wear mark and thus shortened the needles length.

So the float has to be too high to work the needle and seat.

Does anyone have any idea of the correct length required? or is there another way of working around this,with a spacer?


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I am totally unfamiliar with this European Zenith, however:

Most carburetors produced in the USA during this period have a "bowl drain" (often just a plug) in the bottom of the bowl. A number of companies manufactured a special tool often called a "J-tube" that could be screwed into the bowl drain hole with the drain or plug removed. The J-tube had a vertical glass column that was open at the top and extended above the top of the float bowl. Gasoline would flow through the drain into the J-tube and obtain the same level in the tube as in the bowl. One could then compare this level to the height of the main discharge nozzle as you stated in your first post.


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Hi Jon,thnaks for the reply. Thats a pretty good idea ( and something i can make with a tube ) although this float is fed from the bottom and the needle seat is therefore in the bottom of the float bowl. it would appear all these types of Zenith use the same principle of the main jet utilizing an air bleed from the tube beside the float chamber. A close look yesterday revealed a small hole near the top of this tube (or well ) which someone has drilled for a grub screw . The air bleed jet is adjustable (the grub screw is possibly to lock the jet ) but this small hole is ,maybe, leaking too much air thus leaning out the mixture at full throttle. After 50 odd years of working on engines i find anything is possible ...ha ha .

Cheers! Ron B.

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  • 2 weeks later...

Whwn i had it running,it would idle beautifully but at medium to full res it would back fire was if it were indeed too lean but also backfire out thev exhaust occaisonaly.. To my old grey haired mind,that indicated a plug lead on the wrong plug >it has a MEA mag with a 1243 firing order . So i will have to observe the intake valves and determiine the firing order as dictated by the cam.

But in the meantime i have discovered that burlen fuel services in the UK had the Zenith handbook on line!. The info in the Dykes book as almost the same but doesn't actaully cover the European versions .

Zenith Caburetters Zenith Service Guide

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  • 3 months later...

Finally I have it worked out,and it was something which had put the car off the road in 1950.... I went as far as running a 75 drill through the main jet and surprise surprise ,it wouldn't go through, although I could see through the jet it had in fact been soldered up inside. I ran a 95 jewelers drill through to clean it out and the car now runs great! .In fact it has a lot more power than anyone suspected it would have...


And yes it is an electric start!. A Rushmore moving armature starter provides the effort.A rushmore generator set keeps the battery charged and it has Rushmore lights .

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