Zenith 175 CD-2 carburettor

Technical questions and answers
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datsta
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Joined: Thu Nov 24, 2011 2:33 am
Location: Whitianga, New Zealand

Zenith 175 CD-2 carburettor

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I've been having starting problems when the engine has been stopped hot for 20-30 minutes. Usually, hot or cold, it starts first pop but it takes 15 seconds or more of cranking with about 1/3 throttle depressed if it has been stopped for a while.

I picked up a 3.5L V8 manifold with carbs on TradeMe, and it seems to be a Range Rover manifold as it has had no restrictors and has 175 CD-2 carbs. These 175 CD-2 have the mixture adjustment at the bottom of the bowl, like an SU. The adjustment nut raises or lowers the jet, instead of raising and lowering the needle as in the 175-CD. The carbs look the same otherwise.

I dismantled the left hand carb and cleaned out all the white oxide corrosion by soaking in vinegar for a few hours followed by brushing and rubbing. I freed and cleaned up the piston and the choke unit. From a 175-CD overhaul kit I fitted a new diaphragm, needle valve, gaskets and O-rings for the jet in the float bowl. The float was checked to be giving the right clearance for the needle valve to maintain float level.

I then removed the LH 175-CD carb and fitted the 175 CD-2. It's very hard to access the bottom rear carb to manifold nut, you need a 1/2" AF open-end spanner about 2 inches long. I see the choke actually feeds both carbs, so even though the cable only operates on one carb, both get the enrichment via a small fuel pipe. It needed some increased idle adjustment before I could set the mixture and idle speed. One of those air flow balance devices would be good, or a CO analyser!

Once all settled down with smooth idle and the mixture set right when lifting the piston we went out for a 150km run. No hard starting issues with several hot starts and the fuel economy appears to be the same.

I wonder why Zenith changed the design? Hopefully the CD-2 might give more fuel economy with petrol now at $NZ 2.12!
Stage 1 V8 hardtop s/w.

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