Carb for single cylinder engine

[JasonBModerator @jasonb]

I've done them with just a ball or flat disc sitting on a ledge so either should work

[John RutzenParticipant @johnrutzen76569]

Thanks Jason, using a flexible fuel pipe and raising the tank as well as making non return valve did the trick. I had it running for about 10 minutes with a rev range of 750 to 1500 rpm. So I am thinking of either making an 1831 carb which has the jet about 2 inches below the intake or modifying this one by moving the spraybar to a similar low position. I think I will get away with the tank in the original position then. I measured the lift I was expecting and it was nearer 6 inches than 2! I raised the tank by 4 inches and it ran ok at that.

Another issue that showed up though is the head joint is leaking. What is the best way of sealing this joint?

[JasonBModerator @jasonb]

Good to know it was a reasonably easy cure.

I tend to use a smear of liquid/instant gasket usually from Halfords but plenty of choice on the net.

[Howard LewisParticipant @howardlewis46836]

What is leaking through the joint?

Gas, or coolant?

If Gas, the ideal joint might be some copper shim folded over, but difficult to make as washer, or the irregular shape around the valves.

You could try bending some solder (Will probably have to be cored, unless you can get some SMALL diameter uncored ) that can be formed to shape and use as a Wills ring. The ends will need to butt together or slightly overlap.

It might be worth carrying out a trial to see what thickness results after tightening down. A thick joint will reduce compression ratio, not that it is likely to be high, so a small loss could be a big percentage change.

A little more torque on the fixings, equally distributed, MAY cure the leak.

You may need to retorque the head after a little running, as everything settles.

Depends on how many head studs you have, but if only four, or even six, be wary of over tightening. You could worsen a blow rather than cure it, if the head flexes.

A screw thread, even a relatively small one, can apply a surprisingly large force!

(I have seen this happen with a substantial cast iron head clamped by six 9/16 UNF bolts! )

Howard

[John RutzenParticipant @johnrutzen76569]

Hi Howard, thanks for the input. I think the cylinder water jacket needed skimming, I think it was an uneven surface I was bolting down to. So I've skimmed it and will try again with a little blue Hylomar jointing. I'm making an 1831 carb for it. The advantage is that the fuel inlet is much further down and it won't be trying to lift the petrol more than 2 inches which I found it would do easily.

[Roger BParticipant @rogerb61624]

Looks like you are getting better running now Any chance of a video?

I will be interested in how you get on with the 1831 carb. Like the road roller engine it seems that very few 1831/Wallaby engines are actually used in locomotives and vehicles

[John RutzenParticipant @johnrutzen76569]

Hi Roger, I will post a video but I don't know how to do it! Do I have to put it on Youtube? I am making the 1831 carb from stock bar as I don't have a casting and I have made it slightly bigger because this is a 30cc engine single cylinder whereas the 1831 is a twin. It looks a better design than the roller carb being a little more sophisticated.

[JasonBModerator @jasonb]

Yes Youtube or similar will be needed

[John RutzenParticipant @johnrutzen76569]

I've uploaded a video on YouTube. MVI 7332 Rumely Oil Pull model engine running. – YouTube

Edited By JasonB on 17/04/2021 13:14:33

[JasonBModerator @jasonb]

Very nicely done, I like the sound of it when ticking over slowly.

[John RutzenParticipant @johnrutzen76569]

Thanks Jason, I wonder if you can suggest what the problem may be. It will run slowly like that and starts very easily but as soon as I try to open the throttle it just dies. I am wondering about that 1831 carb with the automatic air valve. Have you ever tried to make one like that? I'm sorry about the bad quality of the video. I need to get a better camera from somewhere.

[Howard LewisParticipant @howardlewis46836]

Nice work John!

Sounds quite prototypical.

If it dies when you open the throttle, it probably needs some extra, temporary enrichment.

Opening the throttle admits extra air, but if the fuel isn't there, the mixture becomes too weak to run.

In full size, more recent carburettors, there would be a capacity well or accelerator pump, or in the SU and Stromberg Constant Vacuum carbs, a damper for the piston, to provide the temporary enrichment.

Any chance that you could provide a volume of fuel to surround the Main Jet to act as a capacity well?

Howard

[John RutzenParticipant @johnrutzen76569]

Thanks Howard, I'll have to think how I could provide a capacity fuel well. Meanwhile I can easily try enriching the mixture.

[JasonBModerator @jasonb]

The air bleed should allow you to set one mixture for running and then by adjusting the air bleed you don't run too rich at slow speeds. I've not built the 1831 or one like it but have done carbs with air bleed on aero engines.

[John RutzenParticipant @johnrutzen76569]

Hi, I've made a float chamber for this carburettor but I've come across an unexpected problem.. I followed E T Westbury's design for the 1831 carb. He said make the float out of cork and shellac it to stop the petrol soaking into it. I did that but the petrol just soaks in anyway. Then a news item this week said they were going to increase the amount of ethanol in petrol to 10%. Apparently lead free petrol has 5% ethanol in it which is alcohol so it attacks the shellac. I tried a nail varnish, it attacks it too, humbrol enamel , same problem. Has anyone made a float recently?

[pgk pgkParticipant @pgkpgk17461]

If convinced it's the ethanol then consider some 'aspen fuel'. Or it might be worth trying to mix a small amount of petrol with water, shake it up and then let it settle and siphon off the top part. I don't know if it'd work but ethanol dissolves in water quite well (vodka).

Another thought would be to paint your float with thin epoxy as a fuel proof assuming you don't get into weight issues.

pgk

[JasonBModerator @jasonb]

I've not tried it on a float but I use clear fuel proof lacquer on the hit & miss engines, a few coats sprayed onto the float may do the job. I left the float out of the engine I'm doing at the moment as I tend to just test run them the float chamber can be filled from a dispensing bottle and act as a small tank.

[John RutzenParticipant @johnrutzen76569]

Hi , I wouldn't be able to get fuel proof lacquer here in Northern ireland – they won't even send enamel paint. I have gone the epoxy route and have only quite thick stuff but it seems to be ok. I epoxied a small diameter aluminium tube through the centre. Seems to float alright if you don't get too much epoxy on. I wondered if anyone had ever made a brass float?

[Roger BParticipant @rogerb61624]

I made a tinplate float 26mm diameter and 30mm long many years ago. The material was the thinnest plate that the local model/hobby shop had, maybe 0.2mm. The ends were spun in the lathe and the body was rolled around a former. It was soldered up with the minimum possible solder to keep the weight down. The finished item weighs 6.5g and floats reasonably in alkylate fuel (I think the density is similar to pump petrol).

It never worked due to my inability to make a suitable valve at the time. I decided to use an overflow system for my model SU type carb as this would have needed an even smaller float and valve.

[John RutzenParticipant @johnrutzen76569]

Hi Roger, I was thinking of an overflow system but I couldn't think how to make a petrol pump. How did you accomplish that please? I've re-arranged my tank for the Rumely so it's above the float chamber now. I was reading ETW's article about carbs in a 1946 ME, in that he says the jet should be very near the throttle valve. However the 1831 carb has the jet miles away from the throttle – strange? I haven't got the next article in ETW's series on Carburation without complication though.

[bernard towersParticipant @bernardtowers37738]

Just out of interest my Indian had a cork float with the brass hinge fittings glued in with strengtheners that looked like brass panel pins glued in as well, but as time passed flooding was getting a problem so I sourced a new,new one from the states which is 3d machined in some sort of fuel proof closed cell foam, still with the fittings glued in and has not been a problem for over 12 years. Perhaps this material might be a possibility.

[Roger BParticipant @rogerb61624]

The fuel pump started out as a piece of 20mm square aluminium. I have also built a larger 25mm version but the delivery was too much for this engine. The diaphragm is cut from 1mm Viton sheet using the clamping ring as a punch guide. I decided to use a ball and socket at the rocker end of the pull rod so it would stop pumping against a closed outlet (needed for another application). It is driven by an eccentric mounted on the camshaft drive gear. The inlet and outlet are gravity ball valves with 3mm stainless steel balls. Tiny cross shaped pieces limit the movement to 0.5mm.

[John RutzenParticipant @johnrutzen76569]

Thanks Roger, that looks like really nice work. Meanwhile my epoxied cork float seems to be ok. I was looking up fuel resistant foam online but kind find any. Cork is free and if it works I'll stick to that.

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