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Designing a Tee Dee RC carb Empty Designing a Tee Dee RC carb

Post  TexasWade Sat Oct 16, 2021 8:25 pm

I'd like to make a nice little carb for my TeeDee .010, have been reading and looking at a bunch of stuff.  

Notably, the .010 and .020 can be made to respond well as seen on these videos:




Unfortunately, the youtube poster does not share any information about what he's done!

From what I've seen on Youtube, the Norvel engines also seem to throttle very well.  So checking out my Norvel .074 RC for inspiration, I'm not seeing an air bleed hole (per all of my .15-.28 engines).  Seems like the Norvel design might be simpler and lighter than the Tarno carb I had on my .049 back in the day.  So I started to take the .074 apart to look at it, but everything is really tight and the thing looks pristine so I figured I'd leave it unmolested and ask questions first.

From what I can see through the venturi screen, it looks like the... I don't know what the part is called, the spraybar maybe? Where the needle seats... It simply has a cross hole that aligns with the venturi when open and becomes restricted as the throttle arm is rotated.  Is that all there is to it??  Are there no other air bleeds or fuel passages required?
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Post  davidll1984 Sat Oct 16, 2021 8:55 pm

I will try to explain my best The norvel carburetor is less useful for converting to another model because it is installed glued in place a .061 wasp carburetor made on cox .049 engines Both use the same principle The fuel arrives on one side the adjustment screw is on the other on the rotation barrel valve This barrel when it turns it does not just turn it is screwed on the gas supply tube So it will be used as a fuel air mixture regulator Regulates the fuel and air flow The valve does not only control the air the fuel to This way we can get a much better transition between low and high revs. Low rpm = lean mix The more we open the air, the more the fuel opens at the same time Very good system to get the best from our engines this is one tee dee wit a wasp .061 carburateur
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Post  TexasWade Sat Oct 16, 2021 9:34 pm

I'm not sure I understand correctly.   Are you saying that when the barrel rotates to restrict the airflow, the needle valve also closes by some amount?

I'm not concerned about removal of the Norvel carb since I'll be making all new parts scaled down to fit the .010.


Also, cool car! I really like what you've built there =)
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Post  1/2A Nut Sun Oct 17, 2021 1:25 am

Here is a method a air choke using existing NV assembly.

Designing a Tee Dee RC carb Tee_de14
Designing a Tee Dee RC carb Tee_de15
Designing a Tee Dee RC carb 02s-b311

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Post  1/2A Nut Sun Oct 17, 2021 3:02 am

I did a preliminary tests with a nylon tube barrel.
The venturi was loose during throttling, results reasonable.

The tube allowed screws to hold the arm and fill the voids.
Nylon seals well without causing wear to the aluminum.
The drilled out venturi was under bored so the tube had
to be honed down for a snug sealing fit.



And



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Post  davidll1984 Sun Oct 17, 2021 5:08 am

by TexasWade on Sat Oct 16, 2021 11:34 pm

I'm not sure I understand correctly. Are you saying that when the barrel rotates to restrict the airflow, the needle valve also closes by some amount? ... Yes Thumbs Up
Exactly it closes the two at same time test it and if u close air And you screw the needle completely To stop fuel flow When you are going to reopen Take a fuel tube to blow in the air must not pass Then reopen the air valve the more it open The more air circulates in this tube conected To the ( spray bar) A real carburetor is not just a air choke valve All the ways are good some just better than other the norvel a very Good one Hand Shake Thumbs Up
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Post  TexasWade Sun Oct 17, 2021 6:52 am

Thanks David, that was a good explanation and a good idea for checking the function by blowing through a tube.

Also thanks Brad.  The choke seems to work alright and is easy to make, but I have my sights set a bit higher.  I'm very impressed at the throttle response we see when David whack, whack, whacks the throttle in his video.

 But I don't immediately see how Norvel is making the fuel metering adjustment as the arm rotates.  Have been thinking about it all night and I have some ideas that could work, but I haven't worked out anything as compact as the Norvel unit.

Don't suppose anyone has a worn-out or broken Norvel RC engine or carb for sale cheap?  I'd like to get my hands on one of those for a little reverse engineering if possible.
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Post  davidll1984 Sun Oct 17, 2021 7:23 am

As I said earlier the carburetor of a wasp .061 is better made easier to install similar to the norvel model but this fixed with two screws Not glued on Inside the carburetor there is the spray bar it is threaded on the outside The barrel is screwed in places So when it is turned he unscrews and removes pul out the needle from the spray bar at the same time Thumbs Up Very Happy
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Post  TexasWade Sun Oct 17, 2021 7:35 am

Right!!  I think I got stuck on Norvel for some reason *forehead slap*

I'd like to get details on that wasp carb!  Any pics, detailed explanation, actual measurements, or of course carb in my hands would be awesome.
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Post  davidll1984 Sun Oct 17, 2021 8:03 am

This is the engine To look for Designing a Tee Dee RC carb Scree123
Designing a Tee Dee RC carb Scree122
Designing a Tee Dee RC carb Scree124

It is a good engine but with short lifespan Not like a cox engine
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Post  TexasWade Sun Oct 17, 2021 11:53 am

Another Texan!

Thanks a bunch for that one, Fred. That looks like a great score.   I ordered both the carb and needle.  $35.89 including shipping seems fair, especially compared to the frustration of trying to find a suitable donor engine.   And if it arrives all glued together I'll drop it in a jar of acetone or something for a few days.  

Taking a closer look at my Norvel .074 and putting the calipers on it while moving the throttle arm, it looks like I'm getting about .004 or .005" of sideways movement which works out to roughly 40 threads per inch.  Seems reasonable and simple.  I just can't see exactly what screws into what, where things seal up or where the needle engages...YET.  But with the Cox .010 already here and NV parts on order, this project is officially started.

I'm a full-time CNC machine shop guy with unlimited access to all the machines, by the way.  So hopefully, I should be able to sort this thing out and make some cool doodads... we shall see!
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Post  davidll1984 Sun Oct 17, 2021 12:39 pm

I had already thought about doing it but for this small .010 it would be very hard The plan was to make a model similar to a carburetor with air blead mutch Easy to do But I don't have very sophisticated machinery so simple is best To me it is surely possible to do more complex one with the right tools
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Post  dckrsn Sun Oct 17, 2021 6:56 pm

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Post  fredvon4 Mon Oct 18, 2021 6:06 am

Don't thank me yet

I think Ken said he had trouble ordering off the site and had to buy via phone or e mail

we will see if Texas Wade gets a shipped confirmation
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Post  TexasWade Mon Oct 18, 2021 10:12 am

@fredvon4 wrote:Don't thank me yet

     I think Ken said he had trouble ordering off the site and had to buy via phone or e mail

we will see if Texas Wade gets a shipped confirmation

Yepper, I'll let you know. Looks like my card has been charged, so hopefully that means stuff will be heading my way very soon!
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Post  TexasWade Thu Oct 21, 2021 7:45 am

Let's see what you guys think about how this is looking.  It's actually about .10" shorter than the original Cox screw-together venturi/needle valve assembly.  It's still a preliminary design but should end up pretty close to what I've got now.  I might have to change the needle valve taper and some screw thread pitches or whatever.  Stuff I won't know until I try to run and tune it.

I haven't received the NV carb yet since I just ordered it a few days ago, but I was able to see enough of my .074 carb to see basically what's going on in there.

Designing a Tee Dee RC carb Carby_10Designing a Tee Dee RC carb Carby_11
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Post  davidll1984 Thu Oct 21, 2021 7:55 am

I like the simple design With the carburetor attached in one simple parts In addition, made of aluminum, it would be possible to anodize it to color it. I can't wait to see the result Small Cox Logo Babe Bee .049 RC Plane Thumbs Up
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Post  TexasWade Sat Oct 23, 2021 9:26 pm

@fredvon4 wrote:Don't thank me yet

     I think Ken said he had trouble ordering off the site and had to buy via phone or e mail

we will see if Texas Wade gets a shipped confirmation


Carb arrived today, that was pretty quick!

It looks like I probably won't be needing it by the way since I already learned from my .074 without having to destroy anything.  I'll hang onto the new carb at least until I get a chance to run a prototype of the thing I'm trying to put together, and then this carb will be up for grabs if anyone is interested.

Will be a couple weeks or maybe a month before I can make parts for my prototype though since (fortunately!) my shop is busy right now and I have paying jobs running on all machines.
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Post  TexasWade Sun Oct 24, 2021 6:25 pm

I got my various parts yesterday for the .010 including a new glowhead and piston rod reset tool.  I was a little nervous about setting the rod after reading about it, but I was very careful and reduced the end play from .009" down to maybe .001" or so. Just to the point where I wasn't quite sure if I could feel it moving or not, but the rod could still move side-to-side freely.

I definitely wanted to be sure the engine was ready to run before frustrating myself to tears with an untried carb setup, so there she goes!  Funny thing was, it ran about 10 seconds on the very FIRST flip!  I was amazed!  And then as it took me the better part of an hour to get it to actually make a sustained run, I became less amazed!  I think there must have been a tiny bit of gunk lodged in a fuel passage somewhere and when it finally came loose, it found its way into the cylinder.  The engine didn't want to turn over... felt like it was hydro-locked or something.  Removed the cylinder looking for too much gas or whatever I could find and wiped the piston down, after which everything seemed just fine.  I never did see whatever it was, but she got a lot happier at that point.



Also uhhh... seems I might have bought a new-in-box Tee Dee .020 and a slightly more experienced Tee Dee .049, haha!  I mean OOPS! Oh well, I got pretty darn good deals on both of those I think, since I've been watching the ads for such things for several weeks now.  Long-term goal is to carb all 3 similarly.
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Designing a Tee Dee RC carb Empty Fledgling

Post  Coxfledgling Mon Oct 25, 2021 6:30 am

Hi cef, I am following this thread and the silencer one with interest as I am after Td09 RC carb and exhaust, but realise one may never turn up.

I was thinking of getting a big if RC carb, the 15 one, and adapting it to fit, or getting all the readily ? available parts from exmodelengine/Cox international and making a carb with those parts.

I have some alloy square section bar, a 4 jaw Chuck and small lathe.

One thing is still puzzling me...

The black plastic RC control arm seems to have splines in the hole, but I cannot see splines on the brass spray bar end, and I assume the control arm is held in place by an "e" clip on that side.

I also assume that end of the spray bar is blind with no hole...

Please advise...

I have not done a drawing with dimensions yet and will ask of that data when I am at that stage.

Mecoa has been mentioned but getting stuff from them to UK is problematic.

I have a Cox peewee 20 I am considering parting with, just bouncing an idea here, might someone on here be warmed by a swap, for mecoa parts ?

Just a germ of an idea but I can't see me using the peewee, but then again micro RC stuff is quite light these days...
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Post  balogh Mon Oct 25, 2021 8:38 am

Hi Coxfledgling,

the black throttle arm mounts on the splined end of the rotating throttle drum with an e-clip, and the rotating drum  is a separate part of the carb, it is not built together with the spraybar.

The spraybar itself has a metering hole at its tip that protrudes into the carb. The fuel enters the spraybar under the black plastic fuel nipple, and flows along a flattened length of the bar until it hits the hole where it enters the metering chamber. The NV tip will change the free cross section at the spraybar tip through which the fuel enters the carb body.
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Post  Coxfledgling Mon Oct 25, 2021 10:03 am

Thanks balogh, I will have another look at the spray bar and suss out how that's located/driven/rotated etc. but I think I understand.

The servo arm/spray bar "drum" is located by the small spigot on the end of the spray bar and driven by a "flat" or even a pin perhaps ?

I have another looksee...thanks.
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Post  balogh Mon Oct 25, 2021 10:37 am

The drum is positioned axially inside the carb body by 1 of the 2 screws, actually the rear one, here on the right side - the other one is a air-bleed adjusting screw. The screw also limits the rotation of the drum, so that the approximately 1mm opening  at full closure of throttle drum - as just seen on the photo -can be set for the idle...refer to the R/C carb description among the Instruction Sheets "Tee Dee R/C  .050..."


Designing a Tee Dee RC carb Td_rc_11



The spray bar is to be pushed into the carb body from the drum side. It has a collar that will position it in the carb body. I actually CA glued this collar into the carb body otherwise fixing the nut on the NV end of the spray bar is rather difficult. If you follow this recipe, make sure the CA will not get into the tiny hole on the spray bar tip
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Post  944_Jim Mon Oct 25, 2021 3:59 pm

If yuu guys are robbing AP .061s for their carbs, I'll be glad to buy the left over engine(s)!

If you guys want Norvel carbs, I'll be glad to trade my carbs for Norvel venturies. I have one or two .074s, and one .15, and lastly 1 .25...all with carbs. I'd rather have venturies. The bonus with Norvel parts is that the needle valves fit both carbs and venturies.

Jim in NE MS
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