Engine detail question (Airfix four-stroke engine)

[Bainford]

It would have been quite nice, for this large scale model, if the parts breakdown was a bit more comprehensive. Painting and detailing would be much easier with more separate parts. A cut-away of the carb itself would have been a nice touch. Anyway, I must say that your metal finishes are looking great. Very authentic.

[robdebie]

  On 2/18/2022 at 6:54 PM, Ace-Garageguy said:

First impression is it's a kinda sorta vintage Amal side-draft carb. Look at some online photos, and we'll go from there.

http://amalcarb.co.uk/

EDIT:

EDIT 2: The velocity stack would almost certainly be a separate part, not cast in unit with the carb body.

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Fantastic! That will surely help. Those Amal carbs really look a lot like the Airfix thing. I just discovered that I don't see a fuel line, or a throttle cable, to name some esstential components.

Regarding the color, are those Amal carbs made from Zamac / Zamak or similar?

I *just* finished filling and sanding the transition between the body and velocity stack, grr....  But I always thought that casting it all in one piece wouldn't be easy in reality. Back to the drawing board..

Rob

Edited February 18, 2022 by robdebie

[robdebie]

  On 2/18/2022 at 8:15 PM, Bainford said:

It would have been quite nice, for this large scale model, if the parts breakdown was a bit more comprehensive. Painting and detailing would be much easier with more separate parts. A cut-away of the carb itself would have been a nice touch. Anyway, I must say that your metal finishes are looking great. Very authentic.

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Absolutely! I spent so much time on masking, it's not funny. If I was ever to build something similar, I would try to break the parts up, and replace as much as possible with metal hardware.

I hadn't considered cutting away the carburetor, but indeed that would totally fit with the rest of the model. But with the finish line in sight, it's really hard to do that right now..

Rob

[Ace-Garageguy]

  On 2/18/2022 at 9:35 PM, robdebie said:

...Regarding the color, are those Amal carbs made from Zamac / Zamak or similar?

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Yup. Zinc alloy.

[Ace-Garageguy]

  On 2/18/2022 at 9:35 PM, robdebie said:

I *just* finished filling and sanding the transition between the body and velocity stack, grr....  But I always thought that casting it all in one piece wouldn't be easy in reality. Back to the drawing board..

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Good news: this one appears to have the velocity stack cast in unit with the body. Maybe.

 

Edited February 19, 2022 by Ace-Garageguy

[Ace-Garageguy]

  On 2/18/2022 at 9:35 PM, robdebie said:

... I just discovered that I don't see a fuel line, or a throttle cable, to name some esstential components.

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Throttle and mixture cables on that one go in from the top, into those nut-like things.

Study this, parts 10 and 11:  https://www.jrcengineering.com/technical-support/amal-concentrics-tuning-and-jetting/

Edited February 19, 2022 by Ace-Garageguy

[Ace-Garageguy]

  On 2/18/2022 at 9:35 PM, robdebie said:

... I just discovered that I don't see a fuel line...

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The fuel line would go to a banjo-fitting on the side of the float chamber, just to the side of the velocity stack on your model.

Scroll 2/3 down the link below, page 14 if it displays as a PDF, look at parts 15-18 on what appears to pretty much be your exact carb:

https://static1.squarespace.com/static/547e5122e4b0193d67f28396/t/5854ddf6725e25b3b4c06d52/1481956877861/Amal+MK2+Carb+Manual.pdf

Edited February 19, 2022 by Ace-Garageguy

[robdebie]

Bill, another big thanks for all your help! I think I now understand most details of the Airfix carburetor, and modified the kit parts a bit. I scribed a line around the velocity stack, to indicate it is a separate part, and to serve as a paint demarcation. I cut off the set screw on the left, glued in a piece of thread, rolled a spring from plastic rod, and reinstalled the screw head. On the top side (right in the photo) I cut off the two very unround cilinders, and replaced them with 3.5 mm tubing. Maybe I will add throttle and choke cables coming through them.

On the right side of the float chamber I cut off the simulated cut-of fuel tube. To make its function clearer, I replaced it with a piece of tubing that I gave barbs by using my motortool as a lathe.

I just applied a layer of Mr Surfacer to check build quality. Painting will start tomorrow. Finding a paint match for zinc might be a problem though..

Rob

Edited February 23, 2022 by robdebie

[Bainford]

Huge improvements. Well done.

[Ace-Garageguy]

  On 2/23/2022 at 8:30 PM, robdebie said:

Bill, another big thanks for all your help! 

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You're very welcome, sir. Beautiful work.