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Daimler Carburetors

Technical issues not related to a DLOC car marque, eg tyres, ethanol, other car makes, etc. and legal, political and insurance
Stan Thomas
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Daimler Carburetors

Post by Stan Thomas »

Would anyone with an early (sleevevalve) car fitted with Daimler's own carburetor care to exchange notes regarding their set-up and tuning, given there does not appear to be any published information available, other than a brief description in the drivers' handbook. Those with such a carb will know they are a constant vacuum device similar in principle to an S.U. but with quite an an elaborate arrangements of multi-jets and interchangable venturi plates etc.

That said, the particular problem I have is that whilst the car can return a reasonable mpg, it runs so exessively rich at tick-over it soots up the plugs, and which I have measured to be two-and-a-half pints of petrol in ten minutes!!

I can see from the design that when the cold-start primer is operated, the air passage to the slow running jet is shut off (as shown in the drivers' handbook diagram) - that is until the shoulder of the needle valve which activates the primer circuit wears, which means the carb could now be drawing in fuel though both the slow running jet and the primer jet. Could I be correct on this?

What leads me to suspect my thoughts are on the right track is the manifold vacuum reading is only about 12Hg, given of the amount by which the throttle butterfly has to be open to provide sufficient air in trying to compensate for the exessively rich mixture. I also have a rythmetic "hunting" in the exhaust which is symtomatic of a rich mixture and the slow-running air screw adjustment seems inafective.

Belive me, I've tried all the "usual things" (thus quoting Claude Raines at the end of "Casablanca"), so any feedback would be most appreciated.

Regards to all,

Stan.

P.S.
Yes! I know fitting an easy-tuneable S.U. would solve the problem, but that defeats the objective of preseving the car for posterity in an original condition.

qantasqf1
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Joined: Mon Mar 07, 2016 10:13 pm

Re: Daimler Carburetors

Post by qantasqf1 »

Stan, volume 3 of H. Thornton Rutter’s Motors of Today (beautiful series of books BTW) deals with these beasts. I can only download 4 of 7 attachments at a time (bloody nuisance) so I’ll have to do it in 2 replies.
Cheers
Steve
Attachments
365C1773-82AB-4B60-88C4-3D7681AECBBE.jpeg
95744600-6F62-4073-B750-B30EA67F1CCB.jpeg
F57459EA-1EC0-4A65-B8D3-8DE16EB0D401.jpeg
2C587797-B7E9-415B-B8D0-4750368A351A.jpeg

qantasqf1
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Re: Daimler Carburetors

Post by qantasqf1 »

Part 2:
Attachments
02A65AE9-3177-493B-94B7-CE36421D3A39.jpeg
EAC57F00-5853-4F52-A2E6-00A16F4FF460.jpeg
18D8DE81-6EA1-4A3D-9F81-E8E95D303C21.jpeg

Stan Thomas
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Re: Daimler Carburetors

Post by Stan Thomas »

Thank you for your very helpful and informative reply - which also shows our fellow enthusiasts just how elaborate these early Daimler carburettors were.

I've been "through" the carb three times now - checking every possible source of what might be causing the exessively rich mixture at tick-over (Which wets the soots the plugs), from setting the fuel level in the float chamber to 1mm below the jet orifices to vacuum testing the seatings of the primer valve circuit - but to no avail.

The major suspect is the primer valve which when operated from cold allows neat fuel to be drawn into the manifold downwind of the throttle butterfly - but all that checks out fine having made up adaptors to isolate the internal passages to apply a vacuum test.

The only adjustment as such is the slow running air screw, which seamingly has very little effect as the rythmetic "splashy"exhaust note does not alter. i'm currently making up the parts to isolate the vacuum servo as it is not unknown for them to draw in air (but that would weaken the mixture anyway - but its worth being part of the process).

If I cannot solve it, I'll "bost it wiv an 'ommer" as we say in Bermingum.

Sydsmith
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Re: Daimler Carburetors

Post by Sydsmith »

Well Stan you do surprise me, you have no fear of the Knight engine which petrifies all but the bravest motor engineers but can't solve a carb problem, strikes me you need to ditch the Weetabix and try some Shredded Wheat to refresh the brain power. :D Syd

Christopher Storey
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Re: Daimler Carburetors

Post by Christopher Storey »

Stan : I have no expertise in these carbs, but I think you are almost certainly right when you suspect a petrol primer defect. The primer is in fact very similar in principle to the electric "starting carburetter" used on SU setups on most Jaguars with a spring loaded needle operated by a small solenoid, rather than a manual lever as here. Might I suggest that you try to isolate the primer , perhaps by removing the "dip in " pipe from the float chamber and blocking its end off. If that cures the hunting, it will prove the point and at least enable you setup the main jet accurately. It will also remove the seizure danger caused by wall-washing. How you then would start from cold might require some ingenuity, but it should at least get you running

Stan Thomas
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Re: Daimler Carburetors

Post by Stan Thomas »

Thanks for your contribution Christopher - something I could try!

Actually, the slow running jet in both my carb and a spare one I have is a nunber 15 - whereas the parts book from 1931 says a number 10 (slightly smaller). So, I soldered a fine wire to the jet to reduce its size - resullt - absolutely not a sausage when I tried to start the engine, even though the primer was in circuit!!!

That said, such is the (too) clever design of the carb that the slow running jet becomes inopperative during normal throttle openings - although due to the design, there remains a propensity to draw fuel through the primer jet and so enrichen the mixture.

I will of course see if I can "isolate" the primer as you say, although starting may prove difficult.

Whilst replying - and I hope the chap who kindly posted the previous pages of "Motors of Today" reads this - may I ask if within the five volumes ther is any detailed refferences to sleeve valve engines please. If so, I'll buy a set as they sometimes come up on Ebay etc.

Why I ask is there appears to be nothing in print of an in-depth technical /design nature available, and what there is by way of published material on sleeve valve engines is very little, which I've been collecting over the years anyway. Certainly there is apparently nothing I can find in the way of Daimler service manuals and info for those who would have worked at their deports and agents.

Remember, anyone who helps me gets a free ride/drive in the car (please bring your own oil).

Regards to all

Stan.

P.S.
Now going to cut my lawns with sissors to relieve the monotony of this lockdown.

qantasqf1
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Re: Daimler Carburetors

Post by qantasqf1 »

Stan, there’s not much on the engine. It describes how to set valve and ignition timing, there’s a cross section of the engine, details of bore and stroke, how the sleeves operate, wiring diagram, vibration damper service, water valve service. Basic stuff, but if you need any of this don’t hesitate etc.
Steve the Chap

Stan Thomas
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Re: Daimler Carburetors

Post by Stan Thomas »

Thank you Steve, it is most kind of you to offer, although I glean from the internet the books are circa 1927 - so they don't cover my particular engine. The basic method of checking and setting the sleeve (valve) timing was the same for all Daimler engines - although the actual timing itself varied from one engine type/size to another.

Many thanks though, just the same.

Stan.

Christopher Storey
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Re: Daimler Carburetors

Post by Christopher Storey »

Stan : looking again at the carb diagrams, you make no mention about the air valve for the primer. Is it possible that this has become closed off/choked up so that neat fuel is being drawn through the primer ?

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