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serious2a

Zenith 361V "non-atomisation of fuel"

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Steve, I've long ago blocked off the hole in the carb body to absolutely no avail, (as I said sometime ago).

I think this thread has run its course and I'm not going to get an answer ( or the necessary 361V flow diagram or even somebody to check and report back on their own properly functioning 361V).

I was going to re- MOT this Landrover, but I have parked it back in its garage where it has sat since last summer - defeated!

I am NOT going down the road of throwing cheque books at new carburettors but I might, in time, if the mood takes me, set to and make up an S.U. conversion using a carb which I already have "in stock".

Meantime , thanks to all who took the time and trouble to contribute to this thread.

I intend to start up a new enquiry re the Perkins Prima I have fitted to my other Diesel Landrover - let's hope I have more luck on that one !

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I hear wat u saying - time to take a 'reprieve' from this problem. Sometimes you end up going round in cirlcles so best to quit - for the moment.

Perkins Prima? sounds even more challenging!

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Yes - but having been searching I don't think one exists. :(

The closest i have found is for an acient Zenith fitted to a model T Ford! It may be in principle representative as it links various jets to ambient air pressure and refers to the same types of jets fitted to later Zenith carbs.

What did you think of that article i posted - Page 6 refers to blanking off a hole in the carb body etc. and references to internal distortions causing air leaks etc.

It might be time to try some radical mods to see if they have any affect.

If I ever find the solution I will let you know.

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Hopefully Serious2A will see this Sven as i'm sure it will help with some fresh new ideas to explore,

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Sven - you have hit the jackpot! Absolutely wonderful - 8 pages of service bulletin - what I've been dreaming about from the start! I'm so excited, I'm replying before even having read the lengthy bulletin but surely the answer must be resolvable now, after detailed examination of the diagrams, etc.

SteveRK - notification of this entry by Sven came through on my e-mail from your posting, so thanks to you for drawing it to my attention otherwise I might never have seen it, having more or less given up on the thread!

I'm a bit busy at present with other matters, but I will be posting again once I have digested the 8 pages!

The petrol Landrover may be brought back out of its enforced hibernation yet!

Must go - Thanks again, guys.

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Excellant - your more than welcome - but Heh - it aint over till the fat lady sings! or in this case till the landy purrs

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One thing I'd like to add is that the so-called "redundant port blocking" is not good. Using this diagram and a bottle of compressed air, I verified that this port is the air output for the economy device. The economy device is supposed to open up an air circuit to help emulsify the mixture (lean it out) during idle and part throttle conditions. If you block the port, the economy device never gets activated. Therefor you get terrible fuel mileage but increased power. I took a 400 mile trip last weekend and I could literally watch the fuel gauge drop every couple of minutes. I got 9 MPG at 60 MPH on the highway. The misture was so rich that I could smell gas in my oil :o

After the trip, I unblocked the port and now I'm getting the normal 15 MPG. But the top end power has decreased a little.

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One thing I'd like to add is that the so-called "redundant port blocking" is not good. Using this diagram and a bottle of compressed air, I verified that this port is the air output for the economy device. The economy device is supposed to open up an air circuit to help emulsify the mixture (lean it out) during idle and part throttle conditions. If you block the port, the economy device never gets activated. Therefor you get terrible fuel mileage but increased power. I took a 400 mile trip last weekend and I could literally watch the fuel gauge drop every couple of minutes. I got 9 MPG at 60 MPH on the highway. The misture was so rich that I could smell gas in my oil :o

After the trip, I unblocked the port and now I'm getting the normal 15 MPG. But the top end power has decreased a little.

A big thank you to all concerned in the above thread - two (or many more) heads are better than one ! I have just finished sorting a friends Series 2A 2.25 petrol that was running like a pig and doing 10 MPG all down to warped mating surfaces on the Zenith and unblocking the "redundant" oriface that some bright spark had filled with RTV in the past. If it wasnt for the experiences quoted in this thread and the intelligent advice from members I would still be scratching the grey matter !

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Well being as its a bank holiday weekend i'll have a drink to that! :lol:

Good to hear that the 'Zenith malody' is being overcome by members!!

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I never got my 361V to atomise to my satisfaction and eventually capitulated.

This is the ONLY certain way of remedying this damned problem - fairly simple and 100% effective!

post-6985-1246560370_thumb.jpg

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Guest otchie1
I never got my 361V to atomise to my satisfaction and eventually capitulated.

This is the ONLY certain way of remedying this damned problem - fairly simple and 100% effective!

not really. Carbs can just wear out you know. Most of the rebuild kits available are completely useless often marking your carb run worse that it did before. Shocking lack of quality.

London Carburettor Exchange will rebuild it properly and it'll even come back shiny :-)

I just changed mine for a a modern copy from the Landrover Orphanage for about £80 and it's been working perfectly ever since.

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O.K. otchie1, point taken. What I should have said was: "This is the ONLY certain way of remedying this damned problem short of replacing with a new Zenith". You seem to have done the next best thing but spending that sort of money was simply not an option so I never contemplated it. I didn't consider my carb body to be worn, let alone worn out, this being judged mainly by the butterfly spindle - the only significant moving part, (the accelerator pump can be disregarded).

I'd like to know what in particular in the kit is shockingly bad - There's not much beyond a couple of gaskets, fibre washers, a diaphragm, and a few jets . What can be so bad? Handy to know if I'm ever faced with tackling the problem again.

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Guest otchie1
O.K. otchie1, point taken. What I should have said was: "This is the ONLY certain way of remedying this damned problem short of replacing with a new Zenith". You seem to have done the next best thing but spending that sort of money was simply not an option so I never contemplated it. I didn't consider my carb body to be worn, let alone worn out, this being judged mainly by the butterfly spindle - the only significant moving part, (the accelerator pump can be disregarded).

I'd like to know what in particular in the kit is shockingly bad - There's not much beyond a couple of gaskets, fibre washers, a diaphragm, and a few jets . What can be so bad? Handy to know if I'm ever faced with tackling the problem again.

gaskets didn't seal properly, had holes in nearly the right places, mixture screw had poor threads so suffered from bleeding, O ring was to tight so deformed on fitting, jets looked okay but judging by the rest of the kit were probably off true with all sorts of sharp edges causing eddies and allowing droplets to form. The butterfly wasn't the same size as the original - nearly but not quite. Carbs really are precision instruments, even small variations can cause havoc. It's not just the moving parts that wear - fuel air travelling at those speeds does a fine job of scouring away brass & aluminium. Then there's the thermal capacity of the thing - you should be able to see frost form on the outside on a chilly day. but at the same time it's sat right above the exhaust manifold. 50 years of that sort of thermal stress can easily cause cracks and warping beyond that which a bit of wet&dry on a sheet of glass is going to cure.

The killer Zenith test is whether it still runs with the mixture screw wound all the way in - if it does then fuel is leaking internally from which you may or may not be able to recover.

Glad you got on with the SU - lovely carb and very well plumbed in from your photos. I always fancied a twin choke webber but I needed a quick fix so went with the Zenith - Mr Ebay gave me a discount voucher so it wasn't as bad as all that. :rolleyes:

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Thanks Otchie1 - I never expected such a detailed and in-depth description, but's it's certainly more than enough to put me off buying 'pattern' service kits! When taken into account all that you rightly day about heat/cold, internal abrasion, etc., the only sure answer has to be a new carb! A re-furbed one would still have the same old Mazak castings which could never be brought back to 'as new' condition, as all that could be done would be ultra-sonic cleaning internally and nicely vapour blasting the outside to give a suitably impressive finish! As you imply, heat stresses and worn air/fuel passageways could never really be contended with.

Unfortunately I didn't think of trying your tip about screwing the idle screw full in to see what happened and it's now too late for that so I'm left wondering.....

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Just to add to the conclusion of this thread, my 'good' 361v which did all the miles, including Morocco and France has now started exhibiting the same bad idling characteristics, and MPG is in the low teens.

I cannot be bothered to go through all the hassle again, and need a new challenge. SO, what is the best SU carburettor to use, which vehicle did it come off, and what jetting changes are necessary. The manifold looks neat, what materials are used?

Any other advice, as this is the way to go.

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The S.U. (1 1/4") came off an old mini (probably 60's 0r 70's). The jet and needle, etc were left as they were and operate just fine. I did a plug check after a 30 mile run recently (hitting 55 on the m/way and more pedal to go!) and they were a lovely mid brown so it can't be too far out!).

The manifold was made up using a 90 degree 1 1/4" bore GF fitting (cut at 30 degrees to suit carb angle), welded into two labouriously cut, bored & profiled 8mm steel flanges (that's where the only real work is), and trued up after welding, on a belt linisher.

The adaption for the air cleaner was made up from a Rover 414i exhaust manifold,(welding two bends together), the tapered section was rolled up specially, and welded to the top of an old damper top cover which just happened to fit the existing rubber flexi tube spot on! The attachment flange to the carb was again hand made but of only about 4mm this time, as it doesn't need to be any thicker. It IS an engineering job, no doubt, but if you have the wherewithall it is definitely worth doing. Any other questions just ask.......

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Cheers for the info, I might give it a go over the winter. Whats a 90 degree GF fitting?

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It's a malleable iron pipe bend, (GF = George Fisher) in this case with a male 1 1/4" thread on one end and ditto female on the other. Available in any mechants dealing with steam/water pipes. (You can also get sharp bends, 90 degree elbows, tee-pieces, the lot). A plumber could probably put you wise to a supplier in your area.

p.s: The threaded ends are removed of course before welding.

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Having had problems with my Series 2A/Zenith 361v I read with interest the exchanges in this forum and think I may have something to contribute. Firstly, I must stress that I'm a rank amateur as far as vehicle engineering is concerned so I'll apologise in advance to those of you who are specialists, and issue a word of caution to the others.

My problem began with the engine stopping when it should have been idling. This strange behaviour persisted for 20 odd miles but then developed into something more disabling. The engine, when under power, would begin spluttering and after a minute or two of this it would stop completely. After a rest it would start again but very quickly spluttered and expired. The RAC confirmed fuel starvation; their engineer saying that he could see the main jet in the carburetter functioning but couldn't see the idling jet working at all. He managed to get things going enough to see me home with a "crafty trick" that he "hadn't used for years", he said. Having got the engine running, he then revved it and whilst it was revving sealed the mouth of the carburetter with his hand until the engine almost stalled, at which point he released his hand. Clouds of black smoke were expelled from the exhaust and the engine recovered. He claimed that this technique creates high vacuum levels in the carburetter which can often remove blockages from jets and air/fuel passageways. It seemed to have worked as I was then able to drive the 2 miles back to base but sadly, by the time I got back the problem was returning.

OK. So having read all this stuff about distorting joint surfaces in 361v, I followed the advice, dismantled the carburetter and lapped all three surfaces; the float chamber, the carburetter top and the emulsion block. I should mention that when I started, I could see no evidence of distortion, however after a few rubs on the wet and dry it was evident that were quite significant high spots (low spots depending on your perspective). It took a good half an hour of continuous rubbing to get all three components perfectly flat and smooth. A carburetter overhaul kit was obtained from Brookwells at Newton Abbott (great firm) and all of the jets and gaskets were replaced with new from this kit, except the slow running jet which was strangely absent from the kit. I checked that I had the complete set and this was confirmed. I checked with other suppliers and their kits didn't include this item either. How peculiar! I soldiered on and re-installed the rejuvinated carburetter (except that it had the original slow-running jet).

The engine started at first try after priming the fuel system with the priming lever on the fuel pump but very quickly it would stop if I tried to let it idle. No amount of cajoling and adjustment of the volume control screw would persuade it to idle. I then thought of the slow-running jet, so I dismantled the carb and removed it. Imagine my surprise when, on close examination I found that it was also a non-return valve with a tiny spring and steel ball inside. Maybe it was this that was sticking? It was certainly impossible to move the ball against the spring by blowing into it. I obtained another slow-running jet from a redundant 361v, this also was a non return valve, however I could move the ball against the spring by blowing on this one. So this was installed in the rejuvinated carb. After re-uniting the carb with the engine, hey presto, problem solved!

What has this got to do with neat fuel dribbling from the emulsion block? Well. it seems to me, that whilst my problem was mainly the result of this non return valve sticking shut, what might happen if it stuck open or the spring failed to hold the ball against its seat?

Finally, a quote from the Zenith documentation pointed to in this forum (wish I had had it in the beginning)"...In certain applications of the 'IV' carburetter the slow-running jet 22 has incorporated a ball valve. The purpose of this valve is to eliminate back bleeding of air into the main carburetter jet circuit." Could it be that if the pneumatics and hydraulics of the carb have been compromised by the distorted gasket surface problem then back bleeding of air might suddenly become bleeding of fuel?

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I understand that in the interest of originality, some series owners wish to persist with the Zenith Carb.

My S1 is fitted with a S3 engine and the ex army engine came with a Webber Carburettor which had been mangled by the wrong idle screw being fitted. I bought a Webber copy for around £70 and it ran straight out of the box, decent fuel economy and 5 years later still performs well, except for running on occasionally when the engine is hot, not helped by 95 octane leadfree petrol. I am beginning to get compression loss on one cylinder so the spare hard seated head will have to be fitted soon.

Because the S3 petrol engine sits high in my engine bay the bonnet interferes with the air cleaner plumbing. I have a pancake filter at the moment but this is suffering from foam fatigue and a replacement cannot be sourced.

To overcome the height problem I have been contemplating an SU replacement a bit like the beautiful solution installation shown in the photo post. But I need to cut down the height a bit or the SU will make dents in my Bonnet, is there an SU with a Horizontal intake? Can the float chamber body be indexed around to do this?

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Rubyeddevon - you have brought this thread back to life after I thought it had run its course ! You describe yourself as a 'rank amateur' but your detailed description and 'handle' on the workings of the carb are very far from amateurish. It's interesting that the slow running non-return jet turned out to be the cause of your problem. I removed this jet and as far as I could tell, no air would pass the ball when 'blown' against its seat but I did not try blowing the other way, simply depressing the ball off its seat to check for spring action, dirt, etc. Everything seemed fine and I just replaced the jet as it was. Of course there was no improvement in the dribbling problem and it was very soon after that that I capitulated and made up the S.U. conversion described earlier in this thread. This now means that although I would like to check this jet again, based on your experiences, I'm not in a position to do so. Although happily I can report that my S.U. conversion continues to give great service - easy starting, good mpg,(a relative term !),& total reliabilty.

Your theorising about the 'flow reversal' in your last paragraph, is definitely worth investigating for others here suffering with the 'non-atomisiation' problem who are sticking with the 361V.

There's good news for you, Reg, as you'll be pleased to know that the float chamber on this particular type of S.U. can be altered to cater for a horizontal installation. (There were older types of S.U. carbs fitted to cars of the 1950's which were horizontal but availability (or the lack of) would probably rule them out).

All you have to do is remove the 1/2" A/F bolt that attaches the float chamber to the main carb body, whereupon you will see a 'timing lug' cast into the body of the carb to locate the float chamber at the standard 30 degrees. Simply grind away this lug using a Dremel-type tool or suchlike and then the float chamber can be rotated to any desired angle - simple ! The tapered joint is not a petrol or airway so accuracy is not of prime importance although naturally you'd want to have the two parts mating nicely. I reckon there's no likelyhood whatsoever of the float chamber rotating in service

Now the bonnet clearance worry is sorted out it's time for action ! If (or when?) you do this mod, I'd be very interested to see and hear about the results. To that end would you put a post to that effect on this thread so that I (and other interested parties) do not miss it if it's under a new heading? Good luck.

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Serious2a - I would be much happier with the SU option even though my problem with the Zenith 361v is now resolved. I am an amateur; the fabrication of the tubular adapter described earlier in this topic is way outside my abilities. So your news about the SU carb modification allowing the float chamber to be positioned horizontally is of interest to me. Does the flange on the SU match the induction manifold or does an adapter still have to be used to match the two disparate items?

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If I get you right, rubyreddevon, you are talking about bolting the carb flange directly onto the manifold ? I thought when you mentioned this in your prievious post you were talking about setting the carb horizontally instead of it being 30 degrees up from horizontal as standard and rotating the float chamber to line up with the body of the carb. The horizontal option is very feasible but the vertical is definitely NOT ! In any case the two attacment studs are in the wrong orientation and the the stud/bolt centres on the manifold and flange are disparate, and if set vertically the oil would run out of the dashpot !

My set-up clears the bonnet comfortably, but getting a 90 degree (as opposed to my 60 degree) flanged adaptor made up, will of course increase the clearance between the dashpot and the underside of the bonnet. It's the only realistic way to go in my opinion, if you're sure you really need this extra clearance.

Here's a thumbnail pic to refresh your memory:-

post-6985-069473300 1282500449_thumb.jpg

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