small carburettors

[steve williams 3Participant @stevewilliams3]

[steve williams 3Participant @stevewilliams3]

hi guys

i have recently completed scratch building a 23 cc single four stroke engine & after a few problems with the ignition & plug failing (which with your help i have now sorted. my problem is, the engine runs sweet on a small lawn mower carb i fitted to it but of course i want to make my own, i have now made one with emultion tube & air screw and a float cnamber BUT i cant scall down the float & get the needle to shut so the float chamber keeps flooding i could make the float chamber bigger & put a bigger float in it but it will look out of place. so i am thinking of making a carb of a different design & would like to buy a book but can’t find one on model carbs any suggestions please.

cheers steve

[Ian AbbottParticipant @ianabbott31222]

A couple of ideas,

 

How about a surface vapour carb, simple to make.  There’s one on my 1917 Audel’s, but it’s buried right now.  I’ll see if I can find it next time I go digging.  A search on the web might turn one up and I think that I remember one in ME a while ago.

 

Or, a diaphragm control, like on chainsaws and such.  Might be a challenge to get right, but when it’s done it could be a standard for others.

 

Ian 

[Les Jones 1Participant @lesjones1]

Hi Steve,

                 The only thing I can think of that would cause your problem is if the hole the needle goes into is too big. If you think of it as a piston it will produce a downward  force which would be the pressure of the petrol times the cross sectional area of the hole. If this force is greater than the than the upward force from the float then the valve will not seal.

There will be a lower limit to the size of this hole dictated by the required fuel flow.  Making the float lighter (If that is possible.) may improve the situation.

Les.

[Ian AbbottParticipant @ianabbott31222]

There’s some interesting stuff out there, here’s a few starters.

(Last post should have read “in” Audels) 

 

http://www.youtube.com/watch?v=KwH5_jKTKd8

 

http://keelynet.com/energy/gunnhist.htm 

 

http://www.wikipatents.com/4030457.html 

 

This last one are US Patent details for a surface carb plus some other related stuff such as fuel injection.

 

Ian 

[Ian S CParticipant @iansc]

If you can get Edgar T Westbury’s book Model Petrol Engines there is a chapter on carbs.Ian S C

[mgjParticipant @mgj]

 

 

 

Edited By meyrick griffith-jones on 11/12/2009 09:06:50

Edited By meyrick griffith-jones on 11/12/2009 09:25:20

Edited By meyrick griffith-jones on 11/12/2009 09:26:02

[Ian S CParticipant @iansc]

You should be allright with a float carb if ETW is anything to go by,he says that floats have been used on motors down to 2 1/2cc,although not usually on less than 10 to 15cc.Personally I have made and fitted a very plain(crude) mixer ie just a venturi with a needle valve,only meassurements were the size and spacing of the studs on the inlet’it was /is fitted to a 3hp hit and miss open crank horizontal motor.The motor(full size) when bought had a Ford Model A carb that sort of worked,so we thought aplain venturi would look better,so the one described was made with he idea of making an improoved one,but it worked so well that its still on the motor about 10yrs on.The only thing I would change,I would make it out of brass,the one fitted is steel.The fuel tank is about6″-8″ below the carb,plenty of suction.Ian S C

[John Wood1Participant @johnwood1]

It’s amazing how many of us have difficulty in sourcing a decent ‘general purpose’ carb design for our various engines. Surely there must be someone out there who has the knowledge and skill to design a reasonably straightforward carb which could be used with a range of designs. Preferably without a casting.

 

I have noticed in many earlier published designs that the carb description is often glossed over with such terms as “…I borrowed a carb from an old engine in the workshop and used that or, “….any reasonable carburettor will do”  or the design is based on a casting which is either no longer available or only available as part of a complete casting kit for an engine.

 

Any takers? I’m sure David would be most interested in a design for ME.

 

All the best

John

[Ian S CParticipant @iansc]

Perhaps,because ETW was a past editor(associate)of Model Engineer David C 1 could arainge theinclusion of parts of Model Petrol Engines or articals that apeared in ME.Also the book was published by Percival Marshall

[mgjParticipant @mgj]

Well I shall make a Wyvern next, and I shall simply take the needle valve assy and helical barrel out of an appropriate sized SuperTigre carb (any will do but I know STs) and graft it onto a float chamber.

 

Fuel regulated, progessive fuel supply, and progresive air opening. Looks better than a little Walboro.

 

Very easy.

[Ian S CParticipant @iansc]

One of the plans that came in ME is CENTAUR by E T westbury,there are 2 sheets and My Hobby store has the plans.The engine has 1 1/2″ bore and 2″ stroke.This is basicly a mixing valve with a throttle valve.Ian S C

[Ian S CParticipant @iansc]

Go to top of page,click on shop,scroll down and you’ll find one or two sets of plans for carbies.Ian S C

[geoffrey ballParticipant @geoffreyball88162]

There is a very useful chapter in Len Mason’s book “Model 4-Stroke Petrol Engines” which you may be able to find in your local library. There are no drawings though. Edgar Westbury designed a very neat carburettor for his “Busy Bee” engine which is fully described in ME 3rd July 1952 and in fact I have used an adaptation of this for the 7 cylinder radial engine I am constructing at present.

[geoffrey ballParticipant @geoffreyball88162]

Correction – should be “ME 3rd July 1952 et al.

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