Tarno Carb. Working Adjustable Air Bleed For TD's - RC Groups
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Jan 21, 2012, 01:20 PM
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Tarno Carb. Working Adjustable Air Bleed For TD's

The 3 pictures show how I made an adjustable air bleed on my old Tarno carb. so it will run reliably and be safely used on an RC craft. The details are as follows to a disassembled carb.:

1.Original air bleed hole enlarged to appx. twice the original size and de-burred both inside and out. This whole size is not critical but keep it at around twice the original size.

2.Carefully flatten face of carb. using #400 wet /dry sand paper on a flat glass surface.

3.Drill and tap a hole on the front flat face of carb. for a
2 x 56 screw. Not a thru hole but appx. 3/16" deep. Requires two tap styles for threading. One a plug tap to start and finished with a bottoming tap. Exact position not measured, but was positioned by eye where shown in the pictures.

4.A small sliding/rotating "door" was fabricated from a scrap piece of aluminum, appx.3/32"x1/4"x3/8". The thickness is not critical except it probably should not be thinner than 1/16" so it can be made to have a flat face. One end was rounded and drilled for a tight 2x56 clearance hole for a 2x56 screw. The mating face of this little widget was carefully flattened using #400 on a glass surface. This was done to insure a good seal against the carb.face.

5.A 1/4" long 2x56 Pan Head Phillips screw and a lock washer secure the widget to the carb. and allow adjustment by slicing the bleed hole very precisely. This whole setup must have a low profile to avoid being hit by the prop. Unfortunately it can not be adjusted with the engine running. Screw must be well tightened to avoid loosing setting and hardware due to vibration.

Result: 7k to 18K at 5800' ASL., Hi-Comp head + 1 gasket, and Sig 25% fuel. My altitude may have had some effect on the results. The low enough idle, smooth transition and adequate full throttle resulted in good enough performance for 1/2A RC flying with 5x3 "Rubber Duckie" prop. The results are steady and repeatable which is contrary to what I was getting with an unmodified stock carb. In all, it now works as well as the latter day RC.05 carbs sold by Xenalook and X Model Engines.

Only major downsides to this modification are: New Tarno's are no longer available, carb is heavy, two taps and two drills are expensive, and stock carbs are hard to find and are usually quite expensive. Revisited RC.05 carbs. and "Dickybird" throttle sleeve/venturi modded engines work better in my opinion from my own experimentation.

Time permitting, I will try to make a followup post that explains why I think this modification works if anyone is interested.
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Jan 21, 2012, 09:46 PM
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I'm confused??? Where did everything go that was posted here?

Jan 22, 2012, 07:02 AM
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Confused/ Tarno Carb Airbleed

Pat, I don't understand your question.. What do you mean: Where did everything go that was posted here?
Jan 22, 2012, 07:29 AM
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Well...I did say I was confused! You started the exact same thing on RCU on the 17th, and I posted on that one, along with others that did also. When I saw it here, I thought everything was gone. But Nope, Just the same thing, but different place.

Not good to confuse me, because then I have to go take my meds (Work on a plane) So now that you confused me, I have to go take my meds (work on a plane) Oh Wait!!! Thats a Good thing By see ya later, my DR-1 is waiting.!

Jan 22, 2012, 09:32 AM
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surfer_kris's Avatar
There are posts on the cox forum also, just to add to the confusion...
Jan 23, 2012, 07:36 AM
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hlsat's Avatar
This old Tarno carb is good only for engines Cox Tee Dee .049 and .051.
Origin country of manufacture Canada.
Jan 26, 2012, 08:28 AM
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Tarno Carb. Working Adjustable Air Bleed For TD's

To all of you confused folks, I am also confused concerning posting the same writeup on multiple forums. Is there some sort of protocol that states that doing so is not permitted or is it just a community "No-No"?

In the past, I have posted same subject writeups on multiple forums without getting any flack. I have done this to reach readers on other forums that may not be subscribed or reading elsewhere. I don't want to stir up a hornets nest in one of the best and most informative forums on the Web.

Please let me know what the skinny is about this!
Jan 28, 2012, 12:06 AM
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Astronomer1, its a huge no-no and now that you broke the never been written rule you have to post 9 flying videos in the next month...........just kidding,the more viewers the better I say,multiple forums or no.
Jan 28, 2012, 06:58 AM
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Tarno Carb. Working Adjustable Air Bleed For TD's


Last edited by astronomer1; Jan 28, 2012 at 06:59 AM. Reason: Punctuation

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