Carb help

[e-richard]

Hi all,
Newbie here. Learning fast.

Lots of problems with carb leaking fuel. Travels 4-5 miles then floods.
Checked previous forum and I have:
 
1. Inspected float. Its perfect. No leaks.
2. Replaced inlet needle valve. Both old and new ones working perfectly.
3. Thoroughly cleaned all jets multiple times.

Travel a few miles - sounds good, then engine floods. Stop and petrol dripping from carb.
I have done this about 10 times. Clean carb by roadside and all works again. I'm quite adept at this now 

Latest thought:

Seems to be something missing from this hole (see pic below). In one technical note that I found online it seems to say that there should be a "Screw over Capacity Well". In another explosion of all the parts, there seems to be 2 bits called "Progression jet and plug".

I don't seem to have anything in there and from experimentation when I drip petrol into that hole it seeps up through the main jet and fills bowl, which all concurs with the diagnosis above.

So my question to the experts here is what do I need to do, get, buy, steal ? 

Many thanks,

Richard



  carbtop.jpg (Size: 81.1 KB / Downloads: 539)

[Dave Prior]

It's definitely missing something, and I'm sure that's the cause of your problems. There should be a brass insert in the "compensating well". I've only taken them out once in a blue moon but If memory serves it's a long brass tube, from the top it looks similar to the rest of the jets. There are a couple of suppliers for parts, but I don't know how easy it'll be to track down. I just googled "zenith carb jets" and came up with a few suggestions, including "zenithcarb.co.uk".
If it were me I'd find another whole carb, as a spare is often useful anyway. May sound like overkill, but probably easier to source.

[Mike Costigan]

Richard, you are, indeed, missing the capacity tube, see below:



(item 3 on the left hand page, item 20 on the right).

["Slack Alice" Simon]

I am sticking my head above the parapet again.....

but I think some do have a removable capacity tube, but most don't.

Emerging still further - is the capacity tube a fitting on the downdraft bowl, and not on the side draft?

My tourer has excess fuels occasionally emerging from the carb, so I would like to see the replies to this.

I may try putting an extra washer under the needle valve to lower the fuel level a bit.   Maybe, if the level is a little high and the engine mounta a little flexible, a bit of fues could be vibrated out to where it should't be?

Simon

[Steve Jones]

I don't think it's quite that simple. I've just been through a box of around a dozen Zenith float chambers and whilst some do have the tube covered with a cap, most do not. The clue is if the well has an internal screw thread to take the cap. If yours does have the internal thread then yes, you've got some bits missing. If it doesn't have the thread then, like the majority I've just looked at, it appears it's just a drilling in the float chamber casting.

However, if your float chamber does have the internal thread for the cap that's not the end of it as I've identified two sizes of tube in my little stock! One has a smaller diameter drilling through it but no markings I can see to indicate size. The second has a larger diameter drilling and is stamped '2' on the bottom. 

It's a long time since I had any involvement with these Zenith carbs (so heaven knows why I've still got a box of spares) but if your carb does have the internal drilling in the well, email me your address and I'll put the smaller diameter tube and the cap in the post to you so you can try it and see what happens. I have to say though that your problem seems more like the fuel level in the float chamber is a touch to high than anything else though. 

Steve

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Edited: Simon beat me to it with his reply but we're saying the same thing. I have to admit I've a mixture of side draft and down draft Zenith carbs  and more float chambers than carbs so I'm not sure which float chamber relates to which carb in most cases.

A not particularly good photo of the tubes and caps. 

   

[Derek Simmons]

Hi Richard, What car have you got? Model & year would help!

[e-richard]

Many thanks for the wealth of replies. Looks like its getting even more complicated, but a solution feels imminent...

@Dave: Yes a new carb sounds like a good idea, but hard to source and looking further there seem to be many minor variations (see below), but I think you have given us a very good clue to the bit needed.

@Mike Costigan: I have a document with the identical diagram with parts 1-5 marked and annotated in the same font, but my picture call item 3 a "Screw over Capacity Well". However, I have just noticed that our identical diagrams do not actually match my carb. Not sure what thats telling us though? 

@Simon: When I bought a new needle valve, it came with 3 different thickness washers and no instructions. I've tried the thinnest, I've tried the thickest, I've tried putting two washers on - but I haven't tried none - yet !

@Steve: I'll send you a PM with my address etc. The hole does not have any thread. Its about 8mm in diameter, but then about 11mm down into the hole there is a step to a narrower diameter (guess about 5mm). So I wonder if your two part tubes and caps will work ? Judging by the markings inside the hole, it looks like it could have been in two parts. About 3mm down, there is a very slight indentation as if the tube or cap had a very thin O-ring but with the cap simply jammed/wedged in ?  Looking at my rough diagram, does it feel as if the bits you have will fit ?

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@Derek: Ooops, yes, I guess my Avatar is not that clear. Its a 1937 Opal Tourer.

[Derek Simmons]

Hi Richard, thanks for clarifying the model & year of your car. I believe your model has the same engine spec as my 1937 Ruby. I don't know if you have an inline paper fuel filter fitter? My suspicion is that it's tiny bits of debris getting to the needle and seating as you said you temporary cured the problem by cleaning the carb each time.  Flooding is often caused by poor needle seating because even a tiny bit of debris could cause the needle & seating to fail.  When I got my 1937 Ruby I had all sorts of problems to sort out & the carb was one so I'm offering this information in hope it might help you with your carb flooding. I undertook a fair amount of work on my Ruby's fuel system including cleaning out the petrol tank, purging the fuel lines, cleaning the fuel pump and striping down & cleaning the carb. While most debris from the 80 year old fuel tank was removed it is very difficult to ensure it was totally clear. While I had no further flooding problems, I regularly checked the fuel pump filter and found tiny bits of debris in it as the pump mesh filter still stopped them getting to the carb. I also checked the banjo filter so both became regular 'servicing points'! I've had no more flooding since but recently after discussion with a fellow A7OC member I decided to fit an inline paper fuel filter before the pump and only yesterday I checked the pump filter and found it spotless for the first time and I noticed a very fine discolour on the paper of the inline filter so it confirmed very fine bits of debris are still present in the tank and there was risk it could reach the carb at some stage! Why not try fitting an inline paper fuel filter and see if it makes any difference? They only cost around £1.50 from Euro Car Parts and are very easy to fit! One other point, my carb has the capacity well but no plug or tube in it but it runs well. The hole is as per your sketch & description to Steve. I didn't have a clue if it should have the capacity tube in it until I read the enclosed Austinsevenfriends document http://www.austinsevenfriends.com/Austin...20Carb.pdf . Scroll down to 'The slow running jet' and the next paragraph says it all! Hope you cure the flooding soon!

[Ian Williams]

I think Derek is on the money here, a local club member had the same issue, he told me it suddenly started doing this for no apparent reason. We went through all the obvious, even changed carb over, after much quizzing he eventually told me he had changed the petrol tank, one inline fuel filter later problem solved!

[Derek Sheldon]

Check out Sales and Wants. Self promotion at its worse.