Author Topic: Carburretor Thoughts  (Read 20857 times)

Online Roger B

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Re: Carburretor Thoughts
« Reply #120 on: June 01, 2020, 07:48:39 AM »
I made a quick trial with the new carb to see if I got similar results to before. Seems ok  :)

<a href="https://www.youtube.com/watch?v=Lm0jonOZEqY" target="_blank">http://www.youtube.com/watch?v=Lm0jonOZEqY</a>

To start the actual calibration I need to have a constant fuel level  so on with a smaller diaphragm pump and the level control tank. This pump has a diameter of 9 mm instead of 12 mm so nearly half the working volume. I am making the body square rather than round which will allow more flexible installation.
Best regards

Roger

Offline Vixen

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Re: Carburretor Thoughts
« Reply #121 on: June 01, 2020, 04:37:29 PM »
Hello Roger,

I've moved this post to this thread

I believe Perry make a miniature diaphragm pump for model aircraft engines. It's a bit spendy to buy one just to see if they are any good. 

BUT, I do know the diaphragm is not crank driven. Instead, they have a small weight which is vibrated by the engine and this appears to be enough to pump the pump and give small enough delivery rates..

Is this idea worth an experiment on your engine test rig. :noidea:

Stay safe

Mike

« Last Edit: June 01, 2020, 10:23:25 PM by Vixen »
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Online Roger B

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Re: Carburretor Thoughts
« Reply #122 on: June 01, 2020, 06:47:14 PM »
Thank you Mike  :ThumbsUp: I think that would work to feed the constant level tank. As I understand Walbro (??) also use the manifold or crankcase pressure changes to generate a pumped feed. I am developing the diaphragm pump to reach around 0.8 bar as a feed for fuel injection which I am not sure the other techniques would meet  :thinking: May be crankcase pressure on a 2 stroke single could come close  :headscratch:  :headscratch: too much to learn  ::)
Best regards

Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #123 on: July 03, 2020, 07:23:40 PM »
Finally back in the workshop for a bit more work on the fuel pump. The clamping ring was made as before and the pivot was turned from 4mm brass hex using a ball turning attachment. The pivot block and the bell crank were roughed out with a hacksaw and finished to size on the mill.
Best regards

Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #124 on: July 05, 2020, 05:57:45 PM »
A bit more on the operating mechanism. Most of this was done on the small Proxxon machines.
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Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #125 on: July 23, 2020, 06:35:09 PM »
A little bit more on this one. I had originally planned to use 1.5mm stainless steel for the pump pull rod with M1.4 threads on the ends. This proved hard to find. I could have turned 2mm down to size but found an alternative. 1.6mm 316L is a standard TIG welding filler rod so I scrounged one from work and increased the thread size to M1.6. This machined fairly well for something optimised for a completely different purpose. I made a new pivot and locknut from 4mm hex with M1.6 threads and so far it all looks good. Next up are the clamping discs for the diaphragm and the diaphragm itself.
Best regards

Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #126 on: August 04, 2020, 07:54:24 PM »
Next steps with this one. The clamping nuts were made from 4mm hex and tapped M1.6.  A guide bush was made for the central hole in the diaphragm followed by a 1.6mm punch. The diaphragm was then cut from 0.5mm thick Viton sheet as before.
Best regards

Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #127 on: August 04, 2020, 07:55:13 PM »
-
Best regards

Roger

Offline Admiral_dk

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Re: Carburretor Thoughts
« Reply #128 on: August 04, 2020, 09:40:39 PM »
Looks like the punch makes some very sharp and well defined holes in the diaphragm  :ThumbsUp:

Online Roger B

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Re: Carburretor Thoughts
« Reply #129 on: August 05, 2020, 06:27:41 PM »
Thank you Per  :ThumbsUp: I have found that these very simple punches work well for gasket material as well as Viton sheet.
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Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #130 on: August 09, 2020, 07:03:21 AM »
The valves were made as before. The inlet valve was turned from 7mm brass hex, the outlet valve is a modified Regner union. I still had enough of the milled cross to make the stops. The body and the valve parts went into the ultrasonic bath together with the parts of the new fuel injection pump. The seats were formed by giving a 3mm ball a light tap with a brass rod and the valves were assembled and checked. I turned a 6mm dia. spring seating to go on top of the diaphragm nut and assembled the pump. A quick check with water showed good suction and the level rose around 5mm with each stroke.

Next mounting the pump on the engine and making the overflow chamber.
Best regards

Roger

Online Roger B

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Re: Carburretor Thoughts
« Reply #131 on: August 18, 2020, 05:36:55 PM »
Some more, rather slow, progress on the fuel pump.

The mounting plate was cut from 3mm aluminium sheet and screwed to the back of the timing gear housing. The eccentric strap will be cut from a length of 25mm wide 2mm thick brass and the eccentric is turned from a dog end of 25mm diameter mild steel. With the light loads I don't expect any wear problems. I have used a similar combination for the fuel injection pump on the horizontal engine.
Best regards

Roger

Offline Vixen

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Re: Carburretor Thoughts
« Reply #132 on: August 18, 2020, 08:56:26 PM »
Hello Roger,

I'm still following along.  :ThumbsUp: :ThumbsUp:

It's been a long detour making the fuel pump, before you can start testing the SU carburetors again.

Stay safe

Mike
« Last Edit: August 18, 2020, 08:59:47 PM by Vixen »
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Online Roger B

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Re: Carburretor Thoughts
« Reply #133 on: August 19, 2020, 05:47:53 PM »
Thank you Mike  :)

Time is limited at the moment but I am plodding on. The excentric was turned to 18mm diameter in the independent chuck and then the strap mas set up to bore out to 18mm. Back to the 3 jaw chuck to part off the excentric and then some hand work to finish off the strap. The 18mm bore was slightly off centre but looking at the picture of the setup I can see that the centre was not quite on the mark. There is enough material to recover the problem.
Best regards

Roger

Offline steamer

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Re: Carburretor Thoughts
« Reply #134 on: August 20, 2020, 12:08:56 AM »
Has anyone attempted a sliding plate carburetor?...instead of the usual cylindrical throttle?

Can anyone point me in the direction of one with a set of plans?...

Dave
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