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Title: Aprilia "big Zenith" carburettor Post by: Tony Stephens on 03 July, 2013, 07:37:59 PM I have unearthed what I expect will turn out to be a "big Zenith" conversion, as we used to call them in the 1970's when my Aprilia ARX 560 had one. Unable to get it to run properly on the carburettor, I dropped it in at Zenith in Honeypot Lane London NW, and they rebuilt it completely, jetted it appropriately for the Aprilia from their records, and gave me a bill for just over £3, after which the car functioned perfectly. From my researches/recollection, the model no is 36 VI9, a downdraught version of the sidedraught 36 VI2 which was fitted as standard to prewar Riley 1 1/2 litre cars if you didn't have SU's.
Firstly:are my part numbers correct - can anyone provide a web link to information? Secondly, what should I pay for such a carburettor if in good condition? Thanks for the help Tony Stephens Title: Re: Aprilia "big Zenith" carburettor Post by: DavidLaver on 03 July, 2013, 09:19:06 PM What to pay? A problem that is often resolved with a swap... David Title: Re: Aprilia "big Zenith" carburettor Post by: BlueSky on 03 July, 2013, 10:20:30 PM Tony,
36-VI2 (that's vee eye two) is the downdraught version, I have a copy of a manual that covers it on my web site http://www.narrywoolan.com.au/home/Aprilia_Publications.html My Aprilia had one fitted when I bought it so don't know what you should pay for one. You'll also need an adaptor for it to fit the inlet manifold. Noel Title: Re: Aprilia "big Zenith" carburettor Post by: Tony Stephens on 04 July, 2013, 07:33:38 PM This is really helpful (and the website added to my collection of Aprilia literature - websites didn't exist when I was last around Aprilias).
Keep coming with the information! Thanks Tony Title: Re: Aprilia "big Zenith" carburettor Post by: welleyes on 10 July, 2013, 07:54:12 AM VI2..... and we are still having trouble getting ours to idle consistently. Tried everything we can think of but it is still inclined to stall. It is 'correctly' jetted. It hunts as though too rich but seems correct above idling revs. It is especially prone to cutting out when making a stop in traffic; at a roundabout , for example. Frustrating!
Andy and Stuart Tallack Title: Re: Aprilia "big Zenith" carburettor Post by: lancialulu on 10 July, 2013, 09:35:42 AM VI2..... and we are still having trouble getting ours to idle consistently. Tried everything we can think of but it is still inclined to stall. It is 'correctly' jetted. It hunts as though too rich but seems correct above idling revs. It is especially prone to cutting out when making a stop in traffic; at a roundabout , for example. Frustrating! Andy and Stuart Tallack Just a thought but check ignition timing as if too advanced it will have tendancy to stall. Title: Re: Aprilia "big Zenith" carburettor Post by: BlueSky on 10 July, 2013, 11:09:59 PM Andy & Stuart
A few things to check if you haven’t already. Make sure there aren’t any leaks in the float, a recent problem I discovered that was causing the carby to flood. Take it off any see if it has any fuel in it and put it hot water to see if any air escapes. Along with that the needle & seat could be sticking or worn. Make sure there are no air leaks in the manifold connections and double check the float bowl gasket isn’t blocking anything. The jets fitted to my VI2 are: Main 115 Compensating 85 Starting 120 Economy 150 Slow running 65 Noel Title: Re: Aprilia "big Zenith" carburettor Post by: welleyes on 12 July, 2013, 02:40:00 PM Thank you, chaps!
Jetting is the same as you gave us, Noel; except that main jet on ours is 110. We have just re-checked ignition timeing and it probably was a bit advanced. It now needs a road test but we are ony a few miles from Goodwood and the FoS is on. I gather there are holdup on all the roads heading in the Goodwood direction and it is difficult for us to find a road that isn't being used as a cunning (but ineffectual) short cut. It will have to wait till Monday. Andy and Stuart Tallack |