Author Topic: Carburettors  (Read 6962 times)

Offline Admiral_dk

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Re: Carburettors
« Reply #15 on: December 10, 2013, 08:48:57 PM »
Graham you seems to have solved a puzzle I've been thinking about for a while. On modern motorcycle carburetors, there's a air jet that ends in a premix chamber around the needle jet (Mikuni carby names). The premix chamber helps to atomize the fuel - increasing power and helps to improve fuel economy + reducing pollution => great !

I on fortunately only thought on how to schrink the Mikuni, but you provided an easier solution to make the same function in a smaller scale  :praise2:

Offline Graham Meek

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Re: Carburettors
« Reply #16 on: December 10, 2013, 10:19:28 PM »
Thank you for your kind words, it has always been part of my nature to do a job to the best of my ability.

I could have used a standard commercial RC carburettor but that would have dwarfed my engine, the original Edgar T Westbury design worked up to a point, but I was sure there was something that I could design that was easier to tune and above all in scale with the engine.

By the way I forgot to say that the cooling fan on the engine is thermostatically controlled and runs off the 12v ignition supply.

I have lost count of the number of hours this engine has run, it is well over 50 as my grandson likes to see it running when he visits, which is pretty regular.

Gray,

Offline Mosey

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Re: Carburettors
« Reply #17 on: December 10, 2013, 10:23:53 PM »
At one time I too have had limited success when it came to the carburettor and 4 stroke petrol engines. I made an Air-cooled version of Edgar T Westbury's Seagull engine, made the carburettor to his design and after many hours of adjustment, as described by ETW I eventually reached a stage where the engine would run reasonably well.

This was I felt not good enough as the engine could I thoiught tick-over more slowly and pick up from idle to full throttle a lot better. Plus the plugs were always black indicating a rich mixture. I therefore decided to set about designing a new style carburettor for this engine. It follows the traditional barrel type throttle with an adjustable air bleed, but instead of the plain orifice across the jet as in ETW's design I added an adjustable airflow. I also designed the jet such that it was submerged, there being a small reservoir of petrol available for sudden demands.

The aim of the design was to have a carburettor that would work "straight out of the box" and minimal fiddling. I fitted the carburettor to the Seagull and the engine was tuned and ticking over much slower than before all with-in 15 minutes. The engine would pick-up and accelerate to flat-out without the slightest hesitation, I did write the article up for Engineering in Miniature and it was published sometime back.

If I could fathom out how to load photographs onto this system I would let you see how it was done.

Gray,
Any connection to the "British Seagull" outboard marine engine? had one of those many years ago on my first sailboat.
Mosey

Offline Roger B

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Re: Carburettors
« Reply #18 on: December 11, 2013, 07:26:34 AM »
Mosey,

This Seagull is an Edgar Westbury designed 10cc side valve twin.

http://www.hemingwaykits.com/acatalog/The_Seagull___Edgar_T_Westbury.html

I remember the Brisish Segull outboard well. Most of my boating friends (I was bought up in Southampton) had one on some small boat or tender.
Best regards

Roger

Offline Graham Meek

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Re: Carburettors
« Reply #19 on: December 11, 2013, 10:40:34 AM »
Attached are a few more photographs taken during the build, it gives an idea how I went about the air-cooling and the construction of the combined inlet/exhaust manifold.

The combustion chamber was based on the Richardo design, this has a compression ratio of 6:1 and was the most efficient chamber design for a side-valve engine. (source, Professor Dennis Chaddock, Piston rings and combustion chambers, Model Engineer)

Gray,

Online steamer

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Re: Carburettors
« Reply #20 on: December 11, 2013, 11:19:29 AM »
Really nice work Graham! :ThumbsUp:

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Don1966

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Re: Carburettors
« Reply #21 on: December 11, 2013, 12:05:34 PM »
Really nice work Graham! :ThumbsUp:

Dave


Yup I'll second that.

Don