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Fox 25 control line carb wanted.

Old 10-10-2014, 10:55 PM
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Bill Adair
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Default Fox 25 control line carb wanted.

Hi Folks,

I recently purchased two Fox 25 r/c engines, and after cleaning them up, and replacing all the screws with new socket head screws, plus removing and re-installing one incorrectly installed cylinder liner - they both run great.

Possibly the easiest starting engines I've ever owned! One flip starts hot or cold seem to be the norm.

Now I'd like to try one or both with a c/l carb, instead of the locked open r/c carbs I'm using. These are the carbs that sit on a flat that is cast into the top of the crankcase nose, and the c/l carb is mounted the same way.

If I can buy one or two c/l carbs cheap that would be great. I'd even appreciate a loaner, just to see if there is any advantage using the c/l carbs.

Any help appreciated.

Bill
Old 10-11-2014, 07:18 AM
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Tom Nied
 
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So what you need is a Venturie and needle valve. Have you checked with RSM https://www.rsmdistribution.com/index-2.htm or Bordak http://brodak.com/engines/engine-parts.html?p=4
Old 10-11-2014, 05:01 PM
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Bill Adair
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Hi Tom,

Just sent an email to Eric, thanks.

The carbs I need have been out of production for a very long time, but may still show up in someone's junk box.

Bill
Old 10-12-2014, 06:57 AM
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paw080
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Bill, What you need is a venturi(CL engines don't have carbs...)

and you need a needle valve assembly. The needle assembly is easy to find, some of the big hobby distributers carry O.S. needle

assys, and an appropriate displacement .20-.35 should do the job. The first thing I would do, is call Fox(phone, not email) and ask them if

they still have the parts you need. Fox still stocks parts for engines that are long out of production..


If that doesn't work for you, solicit for some one to make a venture for you; I recommend this forum and the Stuka Stunt Works forum.

Don't worry about the needle valve assembly, many, many different manufacture's spraybar and needles wil fit.


Good luck, Tony
Old 10-12-2014, 03:34 PM
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aspeed
 
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I think it is one of the old ones that has a flange mount with two screws that go on from underneath. Fox did weird stuff in the day. I seem to recall there being an adapter at one time, so it would take regular carbs. I would ask Fox directly, although they have maybe gone out of business, or are thinking that way at least. I had been thinking of making a carb for mine, but, well, I don't really need it that bad.
Old 10-12-2014, 07:59 PM
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Bill Adair
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Tony,

Correct of course, it should properly be called a venturi.

I have several spare needle valve assemblies I could try, but want to see how the stock venturi with Fox needle runs first.

Bill
Old 10-12-2014, 08:12 PM
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Bill Adair
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Aspeed,

That's the one, but there were a couple of different carbs used on that engine.

I'm curious about the c/l venturi though, as there may have been more than one model (throat ID) of that.

My understanding is that Fox has so much government contract work going on, that there are no resources available for model engine work.

Bill
Old 10-13-2014, 05:17 AM
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The rc carb that I have is very small, and then there is a strange butterfly that covers even most of that up. That is likely why it starts so easily. I will admit that I never ran mine yet, I got it with a few others in a box, there was a Fox .15 slant plug in there too.I was going to run up that one the other day, but the drive washer is not right, and I will have to make one. I have to find my knurling tool, and waste a half hour.... same to make a control line carb. maybe more.
Old 10-13-2014, 07:42 AM
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paw080
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Default ...Then there's always....

Hi Bill, a last option is of course, just fly with the R/C carb wired full open.

I have flown three different models with the R/C carbs attached. Since

my models were sport flyers, and your models are sport flyers, it shouldn't

really matter. This last option will not cost you any money.

Again I wish you the best of luck;

Tony
Old 10-19-2014, 06:49 AM
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I am most in favor of just leaving the R/C carb on because in most engines there is more diffidence than just a carb added where the venturi would be, the crank shaft opening for fuel delivery timing is different.
I read an article some time back where a guy did the modification from R/C to Cl to a K&B (I think) he actually took a dremmel to the crank and modified the fuel opening, sorry I searched but can't find it again. I say all this to say you may not gain much by changing to a simple venturi and needle valve so if it works really well now I'd tend to leave it alone. This coming from a guy who fit a OS carb on a Fox 40.

Jay
Old 10-20-2014, 08:13 AM
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On an old Fox, there would be little speed difference in the carb hole dia. for performance. A bigger opening may go a bit faster, and a huge opening could work with a bladder and nitro. It is just a beater Fox which is hardly a performance motor. It is simpler and less trouble if bent in a crash, as well as somewhat lighter.
Old 10-20-2014, 10:16 PM
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Bill Adair
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Aspeed,

Same here on the r/c carb. Strange throttle barrel for sure.

Seems to work well enough locked open, and all it takes is a #2 washer under the idle adjust screw to capture and lock the barrel in place.

I don't have a gram scale to compare the r/c carb and venturi weights, but I'd guess the carb weighs twice as much as the venturi.


Bill
Old 10-20-2014, 10:32 PM
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Tony,

I may just run the r/c carbs, but thanks to Ty I now have a venturi to try.

A friend has the c/l version of this engine on a Flite Streak, and is worried because he is down to his last needle valve. The two engines I received from Ty today have only one needle between them, but the good news is that it's the same as the needles in the two r/c carbs that came with my original pair of engines.

We are into a wet spell here now, so it may be a while before I get out to try the venturi on one of my engines.

Bill
Old 10-20-2014, 10:36 PM
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Jayd3,

I'm not sure there is a difference between these engine, as even the c/l versions say Fox 25 RC on the case. <G>

Bill
Old 10-21-2014, 07:55 AM
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There is no internal differences between CL and RC engines. The only time opening up the crank timing is of any use is at very high RPM - it might add a few RPM in that case. If there were differences from the MFG, there would be different part numbers for the cranks. Same with port timing differences - sometimes its modified by users or engine tuners, but I can't think of any that had different liner part numbers for C/L and R/C.

One thing that I have seen done on combat motors - just cut the neck off the carb and use it as a venturi insert. This keeps the carb from tearing up the front of the motor in a crash, but probably would work better with bladders than with suction. For sport flying, just go ahead and fly with the carb blocked open.
Old 10-21-2014, 11:27 AM
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I have one of these, it is quite crude really, with a flat milled off the case and nothing sticking up for a carb. For the friends c/l needle valve, a simple blob of solder on the hole where the needle valve was, and a remote needle from another manufacturer will work good too. Even if the needle valve is opened up way rich, and a remote needle, it will still be good. I make up a few spray bars once in a while, really just a long pressure fitting that goes in place of the old needle and spray bar. 6-32 or 8-32, depending on the hole size.
Old 12-26-2021, 01:07 AM
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Default Fox carb

Originally Posted by Bill Adair View Post
H

I recently purchased two Fox 25 r/c engines, and after cleaning them up, and replacing all the screws with new socket head screws, plus removing and re-installing one incorrectly installed cylinder liner - they both run great.

Possibly the easiest starting engines I've ever owned! One flip starts hot or cold seem to be the norm.

Now I'd like to try one or both with a c/l carb, instead of the locked open r/c carbs I'm using. These are the carbs that sit on a flat that is cast into the top of the crankcase nose, and the c/l carb is mounted the same way.

If I can buy one or two c/l carbs cheap that would be great. I'd even appreciate a loaner, just to see if there is any advantage using the c/l carbs.

Any help appreciated.

Bill
Hi…I have a fox 25 cl eng and need the rc carb… still interested in tradiing?…Dan

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