Carburretor Thoughts

[Roger B]

I had a chance to make some longer trials on the balcony (at 9°C no one else is going to be sitting out on theirs).

The engine seems to have developed a water leak around the water pump inlet and the cooling fan only works intermittently when the engine is running. I'm guessing electrical interference or possibly vibration. You can see it starting in the video when I switched off the ignition.

I tried the three different trial needles I had made and the best results were with the smallest taper, around 0.6-0.7°. The engine seemed to pick up the load fairly well but I need to get the cooling sorted out so I can run it for longer before it boils.

<a href="https://www.youtube.com/watch?v=aFVkmtzUvWg" target="_blank">http://www.youtube.com/watch?v=aFVkmtzUvWg</a>

[Admiral_dk]

Sounds like you got it to run really well Roger 

The cooling system problem is annoying - but at least easily cured 

[Roger B]

A quick trial after improving the cooling system:

<a href="https://www.youtube.com/watch?v=wXndv7xm82k" target="_blank">http://www.youtube.com/watch?v=wXndv7xm82k</a>

I need to remake the needle as it is a little rough at the idling end and sometimes sticks. Interestingly the profile is almost identical the needle used in the Amesbury V8  The engine is smaller, the carb bore is smaller, the spring is much weaker and the needle is the same.

[Roger B]

I took a few more measurements. At first I thought that the needle was sticking but it was at the idle level. if I pushed it down it came back up to the same point.

The jet is about 0.2mm below the bridge.

The bore is 5.5mm

The bridge is 0.5mm high.

The spring starts to have an effect at ~0.9mm piston lift.

It idles at around 1.7 mm piston lift.

Full open is around 4.4mm piston lift

The jet is 0.8mm diameter

At idle position the needle is ~0.77mm diameter

At full open the needle is ~0.74mm diameter

As long as I have concentricity better than 0.01mm the needle won't jam at the idle position (maybe, don't know  )

I think the piston is reaching full open too soon. If I use a stronger spring  the needle/jet clearance may be too small.

It seems to work quite well but more trials are needed         

[Vixen]

Progress Roger, 

Could you simulate a stronger spring by putting a small weight (or your finger) on top of the piston to stop it rising too far too fast?

Mike

[Roger B]

That's a good thought        I have some small brass weights that go on top of the piston rod from the first trials.

[Roger B]

I tried the largest of my weights, 4.5g, which didn't seem to have much effect  This was a short trial as it ran out of fuel 

<a href="https://www.youtube.com/watch?v=MCmn2VqGorU" target="_blank">http://www.youtube.com/watch?v=MCmn2VqGorU</a>

[Vixen]

Hello Roger,

The piston and weight appear to rise and fall in proportion to the throttle opening. Thats what I would expect to happen.

If you want a smaller piston rise per throttle angle then fit a slightly heavier weight/spring. The needle taper is another matter, you will need to decide if you are rich or lean or OK at each piston height.

Maybe with a longer run we could see whats happening a little better.

It's progress

Mike

[Roger B]

Thank you Mike 

I did a few sums and as the spring rate is 0.07 N/mm the 4.5g weight will cause around 0.5mm deflection. I was able to confirm this by carefully balancing the weight on a spare spring ( I am very good at getting the decimal point wrong when going from g to N  ). I do have some of the same type of spring with a free length of 22mm which I could cut down for further trials. The Amesbury version had a mild steel piston which I was worried would be too heavy and made mine out of aluminium like a full size SU (it's also easier to machine and doesn't rust) maybe he had already learnt some stuff 

Now what I need is some time for some longer trials 

[Roger B]

I made a cover for the fuel chamber as I was getting some splashing and then packed the two cylinder engine and a few useful bits in a box to try it in the welding area at work. Initially it jumped around a bit on the steel table but a spill absorber pad underneath kept it still. I tried adding and removing the load at various speeds/throttle openings which seemed to go quite well. It generally sounded better under load. I didn't take any electrical measurements this time, but with full load the resistance is 1 ohm so I will be getting 60-80 w. The generator and resistor bank heated up quite well and with an extended full load run the engine cooling system was on the limit. A bit more detail work on the needle and spring and I think I can call it a success   

<a href="https://www.youtube.com/watch?v=PzqN-UTOmjU" target="_blank">http://www.youtube.com/watch?v=PzqN-UTOmjU</a>

[Vixen]

Well done  Roger

That was a good result and a nice reward for all your persistence and dedication to the task. Am I right in thinking the choice of spring rate was the main driver? Are you going to up-issue your drawings? I would like to try one for myself

Hope you get the same success with your fuel injection.

Stay safe

Mike

[Roger B]

Thank you Mike   

I am still using the original spring but I think a little stronger might be good  I have attached the latest drawings of the carb and fuel pumps as R12 DWGs (I think you can read them). They are certainly not up to Brian Rumpnow's standards but are hopefully understandable.

I am slowly learning about the diesel injection systems but I think there is at least a year to go with the current rate of progress 

[Vixen]

Thanks for sending the updated files.

Unfortunately I cannot open them. I can still open "CD carb2 R12" dated 13/5/2020 but not the 08/11/2020 version. My AutoCAD says 'created by incompatible version'. Dont you just love computers 

Mike

[Roger B]

I have cleaned the carb drawing and resaved as R12. The start of the file has the correct code so I hope this works 

[Vixen]

Thanks Roger,

Got it this time. 

Mike