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Old 06-04-2010, 07:17 PM   #1
Maine Ronin
 
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Default Carburetor plans?

I got into the idea of building engines because you start with nothing but stock and give it life. That's why I don't like the idea of putting an RC carb I bought on the Jerry Howell Power House or the Webster engines I plan on making. I'd like to make ALL of the engine or at least as much as possible.

Are there any plans out there to download or buy that could be adapted to these model engines?

The venturi systems that are part of these plans don't seem to offer much control and I've heard they are finicky. Any ideas?

Thanks,
Adam



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Old 06-04-2010, 07:38 PM   #2
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Default Re: Carburetor plans?

The one I know of is from Jerry Howell:

http://www.model-engine-plans.com/en...2jet.htm?23,14

I'm not sure it would be a size match for the engines you are considering.

Also, do a search on this site. There are several threads regarding the building of carbs, such as this:

http://www.homemodelenginemachinist....p?topic=8893.0



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Old 06-04-2010, 09:36 PM   #3
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Default Re: Carburetor plans?

Quote:
The venturi systems that are part of these plans don't seem to offer much control
I think you will find that most carburettors use some sort of venturi system, because it is that which gives the fuel lift, vapourisation and mixing. Plus it also helps to fill the cylinder, and once in the correct ratio for good combustion, cram in as much and as quickly as possible.

How well it works, if you make it yourself, depends on how good you are at getting the correct shape and smooth flows, very small tapers and fine feeds. No matter what plans you build to, those are the most critical features required.

Jan Ridders 'vapour carburettor' seems to be different from most fuel systems, and looks to have very good control of the mixture, but I don't know about throttle response.

http://heetgasmodelbouw.ridders.nu/W...r_frameset.htm

Chuck did a simpler modified one here.

http://www.homemodelenginemachinist....p?topic=7931.0


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Old 06-04-2010, 11:50 PM   #4
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Default Re: Carburetor plans?

Adam, we have a couple gentleman on this forum who are brillant when it comes to understanding carburetors. Their names are George Britnell and Steve Hucks. There are probably more, but these two are very active on this forum. Read some of their posts on model carburetors and you might get the information you are looking for.

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Old 06-05-2010, 12:01 AM   #5
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Default Re: Carburetor plans?

A model airplane carb generally uses the spray bar as part of the venturi. They can really be quite simple - a spray bar and needle valve in from 1 side, a rotating barrel for the throttle and some way to limit rotation and maybe adjust idle. Some hav a small hole and a screw that is for air bleed at idel to keep it from getting too rich.

The old K&B engines had a nice example.

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Old 06-05-2010, 03:48 PM   #6
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Default Re: Carburetor plans?

Here is a picture of my vapor fuel tank carburetor. Compared to a carburetor, this thing is dead simple, starts darn near every time on the first pull, and is very easy to adjust, both speed and fuel mixture. I would highly recommend you start with this to get your engines running, then try building a carburetor later. You can also mix wd40 with your fuel (coleman fuel in my case) and it will lubricate your top engine parts.



I used a glass pimento jar because it's about the right size, you can see the fuel level and see if the engine is drawing fuel by the turbulence in the jar. It's also cheap and readily available, at least in the U.S. for about $1.60, including pimentos! The jar is about 1.5" tall and 2.5" diameter. Dimensions aren't critical and most any container will work.

The 6-32 socket head cap screw is the throttle. Nothing special done to it, it threads down to just past the nipple leading to the fuel line to the engine. It's not real apparent in the picture, but there is a spring under the screw head to keep it from turning due to vibration when the engine is running. The split brass sleeve at the bottom rotates to cover/uncover a hole which controls the air/fuel mixture.

I used 7/32 solid brass rod for both pieces because that's what I had on hand. Quarter inch would probably be better. Both rods were drilled through @ 1/8" and shouldered and threaded @ 10-32 to fasten them to the lid with 10-24 nuts. The nipple which accepts the fuel line is 3/16" and is soft soldered to the vertical piece. It also has a 1/8" hole through the center.

Be careful tightening the nuts when you fasten them to the lid. The tube wall is pretty thin and will break easily.

Here's a video of the fuel tank in action.


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Old 06-07-2010, 02:34 PM   #7
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Default Re: Carburetor plans?

Wow. Ask and ye shall receive!

You guys are phenomenal. I hope I can at least get close to your level of skill as I work on my career as a machinist.

And Mr. cfellows, that really is something! I'm sure it can feed the model engines I'm looking to make, but how large an engine do you think that setup could feed?

Very cool stuff. I can't wait to start making stuff. Now I just need to get some machines

Thanks for the help,
Adam



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