New member, question (long winded!) about carburettors

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Jonson
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New member, question (long winded!) about carburettors

Hi. Really enjoying reading this forum, so much info & knowledge here! I've been involved with some lawnmower renovations over the years and have had a go myself a couple of times but I'm far from an expert. My query is regarding the viability of retro-fitting the older Zenith tca carburettor to an a114 Suffolk/Atco engine. The current carb is the Dellorto, and whilst the engine does start and run, in a mostly usable manner, I'm far more familiar with the Zenith unit, which provided they are clean are easy to tune properly.

The engine starts ok, I've cleaned out the Dellorto carb, if it runs rich there's more power but then it doesn't idle well, & whenever the throttle is opened fully quickly it tends to cough & splutter. Admittedly I am being fussy as I've always found that a good Zenith carb will tune easily, rev & idle well, even on a tired engine.

I understand that the governor assembly would be the biggest issue, with the Zenith's using the tried & trusted vane type & the Dellorto the mechanical type, which I've tried adjusting but with next to zero effect. As I have 3 or 4 spare Zenith carbs including the governor vane assembly, linkage & springs etc I'm wondering if this conversion is possible/has been done before? Can I just disconnect all the Dellorto associated mechanical governor assembly? Would the jet sizes in the Zenith tca carb be ok for the 114cc engine? Would a tca13-3 be any better than a tca13-2?

All this is presuming there is a spigot for the vane governor to attach to on the a114 block (same as the a98?) which I've not checked yet!

Apologies for the long-winded question and many thanks for your help.

 

wristpin
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Welcome to OLC

Welcome to OLC

In no particular order. I'm not sure that some of the plus points that you attribute to the Zenith carb  belonged to the instrument itself  but to the design of the engines that they were attached to - slower revving with heavy flywheels. I remember the early A98 engines with the air vane Zenith and they were horrible (my opinion!). In some cases we were removing the A98s and fitting cast iron 75 and 98 cc SIF engines from scrapped machines.

Now fast forward to your issues with the Dellorto carb. I know that you say that you have thoroughly cleaned your example but has this cleaning extended to the gallery behind the welch plug covering the slow running and progression jet orifices. I have experienced Dellortos (not all on Suffolks) that have failed to perform after two sessions in an ultra-sonic cleaner, yet recovered after a manual clean behind that plug. 

I've  scanned some service bulletins relating to issues and modifications to the A98 and A114 engines that may be of interest - particularly the fact that Suffolk themselves issued an adjustable main jet kit to deal with problems that were current back in the day. A similar variable main jet kit was also available under an Aspera / Tecumseh part number to deal with issues that they were experiencing.

EDIT. I forgot that this site wont accept PDF files so I will Dropbox them and add them in a moment .

https://www.dropbox.com/s/eyz0u89k7g6r50f/Suffolk%20A98%20and%20A114%20e...

Jonson
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Hi and many thanks for your

Hi and many thanks for your speedy response.

You are probably correct about the Zenith carbs, my bias towards them is likely just down to my familiarity with them!

You are also right about not cleaning the Dellorto thoroughly enough as I don't recall cleaning the gallery you mention, so I'll be tackling that soon. Mine hasn't got the variable main jet so presumably what I've been adjusting is just the slow running jet, which explains why it only makes any difference....with the slow running...!

I do have an A98 with the Zenith & air vane setup on a 1980 Atco deluxe 17 which believe it or not runs ok. Admittedly not as well as the cast iron engines but light years ahead of my A114.

Once again many thanks for your help.

Jonson
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Edit: Many thanks for the pdf

Edit: Many thanks for the pdf, very interesting. Notably it looks like the A98 acquired the Dellorto carb in 1983 but not the mechanical governor until 1987 so this carb must have been used with the air vane setup for a short time. Also interesting is the change of jets, emulsion tube etc, so as you say the manufacturer was still kind of experimenting with this carb, which doesn't fill me with confidence lol

 

Clive1962
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Hello,   I'm another new

Hello, I'm another new member here :)

Yes, the Dellorto was used with the air vane for a short while.  It made for a carb that stuck a long way out horizontally rather than the neat set up with Zenith...

 

I recall that the governor spring had a rubber "bung" within it, to act as a damper.?  They did not operate nice at all.   The mechanical governor would have come in with change to the A114.

 I also recall that changing the spark plug gap to the larger gap as listed on the posted documents made quite an improvement on some machines  (Only though applies to first type of electronic ignition)   Another thing I recall being advised once by the local travelling service rep, who in our case would have come out of Eckington branch, was in an effort to get things to some sort of operating compromise was to set idle mixture to optimum and then set 1/4 turn richer to allow clean pick up to running speed. Not perfect but they were obviously trying to make the best of what they had at the time.  Clearly things were not good and after I left the mower world there was a change of ignition type and carb type on A114, which I have not seen or worked with.

The batch of A98 with poor machined cam followers was an interesting one too..

 All rather problematical engines...but rather fascinating all the same :)

 

Clive. 

Jonson
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Hi and many thanks for your

Hi and many thanks for your response. It is interesting learning about these engines. It's a shame they were problematical when the cast iron units with the Zenith setup were much better. Thanks for the tips in setting up the low speed mixture, with some trial and error I managed to set it up so the revs pick up cleanly from idle, & it even idles generally ok. It's just when you quickly open the throttle wide it splutters badly. Probably too weak a mixture. Therefore I plan to thoroughly clean the carb and see where we go from there.

These A114/dellorto setups do get bad reviews, I'd actually be interested in hearing of any real world experience of them operating perfectly throughout the full rev range & idling well?

Regards,

Jon

wristpin
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Yes, the Dellorto can work

Yes, the Dellorto can work satisfactorily on the A114  - except, of course, the one that defies all known cures and gets replaced.  Seriously, the adj main jet kit saved a lot of messing around and was 99% effective.

I was interested, nay, surprised to read of an A98 with an air vane governor and a Dellorto. In nearly 30 years in the trade and a few more years at either end I cannot remember seeing one and as yet, a skim through 1980 and 90 parts books has failed to show the elusive beast! Still looking though!

 

 

 

 

 

 

Clive1962
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The carb and then the

The carb and then the "manifold" for Dellorto/air vane for A98 is shown on pages 40a and 40b in the July 1985 spares documentation that left the mower world with me. It still used the ignition cut out governor arm as per the last of the Zenith.

 

Clive. 

wristpin
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Clive 1962, Please post a

Clive 1962, Please post a scan or link, it would be useful to have it on file.

Clive1962
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Here's the "manifold"

Here's the "manifold" ....Not sure about how its going to view on the forum page

wristpin
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Thanks, Views fine. Presume

Thanks, Views fine. Presume that the air vane  pivot pin is exactly the same as used with the Zenith.

Clive1962
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Yes, on the A98 it was the

Yes, on the A98 it was the plastic air  vane on the pressed in pin with the circlip retainer as per Zenith use.  I seem to recall seeing at least one where the inlet had broken  maybe a grassbox put over mower in shed calamity... 

Why was the switch made from Zenith.?  Did they cease to exist at that time and hence this quick Dellorto fix was made.?   I remember a van appearing out side my work one day with a guy selling spares and it was loaded down with brand new last type Zenith...wished I had bought a few but whilst cheap they were still a price relative to my take home then.

C.

wristpin
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The demise of the Zenith.

The demise of the Zenith. Things happen and reasons ( rumours?)  abound; was the tooling worn out and it was deemed uneconomic to re- tool, was it the beginning of emission regs and the Zenith wouldn’t comply or did Dellorto just offer a better deal? Who knows?

Interestingly the last version of the Villiers Sloper gained a Dellorto too. I had never seen one until another OLC member acquired one last year and then I was asked to sort out an old Auto Certes for a local cricket club and that had one as well.

It is said that the demise of the cast iron SIF engines was brought about by the Health and Safety Executive  condemning Suffolk’s foundry and it being uneconomic for them to re-equip to comply.

 

 

Chris G
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The A114's with Dellorto

The A114's with Dellorto carbs and mechanical governors that I've got back operational have idled and picked up OK after a good carb strip. Never had a A98/Zenith which may have been crisper? The late Sloper engine with the Dellorto is on my Marquis

Jonson
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Many thanks for replies, it's

Many thanks for replies, it's all interesting stuff. It's good to know the Dellorto's can work well, it's not so good that mine still doesn't...! I believe I've thoroughly cleaned it, but obvoliously not as it seems to run even worse now! In my experience a Zenith has never been this troublesome. If the adjustable jet kit is no longer available then I may have to consider my original plan - bin the whole setup & retrofit a Zenith & air vane gonernor!

Another possibility might be fitting one of those Tecumseh carbs available on ebay for about £10, they look similar to the dellorto?

Regards,

Jon