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Betsy

Zenith 361V Problems

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I am having repeated problems with brand new Zenith carburettors. I am wondering if anyone else is suffering the same issue. Each time I have repaced the carb, it has run fine for a few thousand miles, then it has started to leak, and flood. I have then found it impossible to get it to seal properly.

I am now on the 3rd unit and its just started cutting out and idling roughly when the car is parked pointing uphill. If the car is pointed down hill it idles smoothly. If I look down the carb venturi when its pointed down the drive, there is no fuel coming out of the main jet emulsion tube, and a nice steady hiss from the carb. If I turn the car around to point up the drive, the idle is rough, and looking down the carb shows fuel dripping from the emulsion tube, accompanied by a lot of sizzling/spitting noises.

I think I am correct in thinking that there should be no fuel dripping from the emulsion tube at idle? I have checked the float and its 32 mm from the top cover face ala' Haynes manual spec. The float needle seems to be sealing perfectly (can't blow any air through the inlet when its turned over). My only other theory says that the fuel must be leaking internally and getting into the main jet circuit somehow.

I am well aware of the heat-warp problem, and have read loads of documents about blanking off redundant airways, refacing the surfaces, new o'rings gaskets etc, but have never suceeded in getting the carb to perform as well as it did when it was new.

Anyone got any experiences or tips that they can share? I am seriously thinking about an SU conversion, where can I get one from?

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It may sound a bit of a bodge, but I fixed rough running by smearing the big o-ring in the middle of the card with a bit of silicone sealant and re-assembled, it hasn't packed up yet... :)

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This a well-known problem with Zenith carbs. The two halves of the casting distort with heat and it has the effect of the engine running on choke all the time. I have a file I can send to you showing the problem and how to cure it. PM me your e-mail address and I'll send it.

Les.

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I too had this problem a couple of years ago, I posted on the old forum, don’t know if it was copied over, I tried all of the fixes and in the end could rebuild the carb in my sleep, Paddock’s are doing the Weber carb for £75 plus VAT which will probably be a more cost effective fix at the end of the day

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I would go for the SU much better in the long run , fitted one to a 2.25 donkeys ago, there was a conversion kit about since then, I made my own manifold adapter ( not hard ) and used a carb of a 2 litre Ital o series. better fuel consumption, and seemed to pull better. I think ACR automotive do a kit HTSH :):)

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Righty ho! all fixed now. Many thanks to Les for the interesting article, I had seen it before but it was very useful in deciding what to do.

I decided that I wanted to keep the car as near to standard as possible, so decided to strip and rebuild one of the Zeniths that I had bought and put on the shelf when it started running badly.

When I closely examined things, it was obvious that the main area of distortion is the emulsion block which attaches to the bottom of the carb top. This lets fuel into the airways that feed the economy valve, and also lets fuel spill into the main jet passage when it sloshes back in the float chamber. This would explain the failure to idle when parked facing uphill.

I used the method described in the document to flatten the mating surfaces of the emulsion, the top and the main body of the carb. Then it was thoroughly cleaned and reassembled with a new gasket set. (got the gasket set off EBAY for a couple of quid).

Swapped the rebuilt carb onto the car this evening, and she runs sweetly again.

Now I will rebuild the Zenith I've just removed, and keep it on the shelf as a spare for the next time it happens.

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I would go for the SU much better in the long run , fitted one to a 2.25 donkeys ago, there was a conversion kit about since then, I made my own manifold adapter ( not hard ) and used a carb of a 2 litre Ital o series. better fuel consumption, and seemed to pull better. :):)

How did you make your own manifold?

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Thanks about the link! I have tried two different old Zeniths and both had the same problem. Engine stalled every time when I braked to stop or turn. Otherwise the carbs were working fine. After fixing the carb everything seems to work fine :)

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I have read somewhere (possibly even on here) that the problem is caused by the carb body not being properly stress relieved during manufacture and that a method of fixing it (after cleaning the carb and sending the missus out shopping) is to put it in the oven and heat it as hot as the oven will go, then cool it down in stages. of about 100 degress, spending about 4 hours at each stage before finally bringing it back to ambient

obviously the carburetter needs stripping to remove all the rubber bits first and the only bits that need to be annealed are the major castings

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