COX engine throttles

mx862 wrote:Finally! Very nice!!

Its hard to tell from the vid... but from what i can see, exhaust restrictor with a carb? seems to work very well! Can you post a picture of the carb? or some more details?


Once again nice job!

thanks guys,
Its not a carb at all, those are in the works but not yet refined yet,the airbleed is absolutely necessary and needs a bit more fine tuning.
What I use on mine currently is basically the definition of a throttle device;I make a simple device to clost off the intake while the exhaust isclosed off as well.
I will have to get some pics this weekend, so stay tuned lol

Thats funny as im currently working on something similar but mine will be like a carb, with a rotating barrel... been " ghetto machining" aluminum on my drill press with a dremel..what fun..

Anyone know what thread size is on the 010 venturi and carb body?

mx862 wrote:Thats funny as im currently working on something similar but mine will be like a carb, with a rotating barrel... been " ghetto machining" aluminum on my drill press with a dremel..what fun..

Anyone know what thread size is on the 010 venturi and carb body?

Thats how I do it too but I also do have a lathe, I actually don`t know the thread sizes,I use production pieces in my design and don`t need the sizes to make mine.

The carbs are tricky as the volumes make a huge variable and I havn`t gotten one to work decent without an adjustable airbleed.

Air bleed carbs have been done before, i going to attempt to make one later, im basically using the dimensions from that carb drawing i posted, i got 2 blanks "machined" one for a choke type carb, and one for an airbleed type deal.

Here is my amateur attempt... found an aluminum bolt in the
parking lot, figured id put it to use , the barrel is a small ground down 3mm feathering shaft of a gaui 200, the whole thing is air tight and smooth, not too bad considering i dont have a lathe, but could be better.

Im now convinced i could make a crude airbleed carb.. or choke device.. given enough time and patience.

I need to find out the thread/pitch size for the 010 venturi, i need to cut the threads to make this thing work.


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Edit: I forgot to mention.. i still have to drill the 3 small fuel ports before i thread it, or grind down an existing venturi, fill the cavity with alumiweld or some such type of thing... and re drill, i played around with aluminum brazing a few years back.. trying to fill scratches on an aluminum swingarm on a 1984 CR250R i was restoring, Ha... that didn't work too well ended up getting a new swingarm, but i did have success on some small stuff.

Well... here is the monstrosity i came up with my choke device.

I ended up sacrificing the venturi, as i got another engine on the way, ground it down and bored it out to press fit the Contraption on, then used a product called "uniweld" to solder the whole thing together, basically fancy aluminum flux and lead free solder, but it worked really well, and the whole thing is solid now, took a bit of reheating and tweaking to make sure it was square... I did this so i can keep the NVA.

There is 1mm of clearance between the intake and the prop... good thing the prop doesnt flex much

I dont think the engine will even start with the damn thing on... will find out tomorrow. Never the less i had fun making it.


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as long as you havent blocked the small holes in the venturi, and you have still got about the same id as the venturi had, it should run

and if you have got a good airtight seal on the barrel i think you will be surprised how well it works


well done

a.

Thanks! the holes arent blocked, i learned my lesson on my steam engine, i fill the shaft in both the venturi and choke device with wet balsa, not fun getting it out, but it stops the solder from going places it shouldn't, the barrel is a perfect fit, i drilled the hole just under 3mm and honed it out, then lapped it for the final fit, the is zero play, and no leakage, oiled, i tested it with my airbrush compressor, at 8psi.

Will see what happens tomorrow.

Well it works... but its very very sensitive, it did not like the new needle valves, ran much better on the old one, don't know why... the needles are slightly different, but it shouldn't make than much of a difference, there is an annoying delay in throttle response, i think with a few adjustments it could be improved, idle rpm can be sputteringly low, but quickly opening the throttle kills it...

Will try with an exhaust restrictor in the next few days and see if things improve.

Will see if i can get a short video in the next few hours.

iff you have a good idle, and it dies when you open the throttle quickly, chances are you will need to reduce the size of the venturi.

this will decrease air pressure in the venturi/increase the amount of fuel that the carb will be trying to draw, and allow it to respond faster.

or make a throttle pump!!


cheers
a

ado1974 wrote:iff you have a good idle, and it dies when you open the throttle quickly, chances are you will need to reduce the size of the venturi.

this will decrease air pressure in the venturi/increase the amount of fuel that the carb will be trying to draw, and allow it to respond faster.

or make a throttle pump!!


cheers
a

Dont tempt me... i have enough "projects"

On one run i really turned in the needle, i think it was out 2 1/2 turns, no more, and things really improved.

Thanks for the tips, i was thinking about that.

It feels as though its getting too much fuel, as it takes a second to burn it off, as mentioned running lean really helped.

Now i still havent replaced the piston, and compression is what i would call low, i run 25& extra castor, and that helps seal things... have an almost new motor on the way.. so will see if things improve with it, i also ordered a laser tach so i could give accurate rpm numbers for both throttles.

if it is improving with when you lean it out, that is another story....

that is where the air bleed(discussed earlier) starts to work.
allowing a little extra air in at idle to make it leaner, but the small amount of air at idle, doesnt have much affect(or gets blocked off) when at wide open throttle, so performance isnt effected.

a.

An airbleed wouldnt be too hard to add, something to think about thanks, im uploading a couple of vids now.

The needle valve settings are much different, with this design, with the exhaust throttle you can just set it and leave it, on this one the needle must be opened 4 1/2 turns then turned it everytime.. kinda like on a stock engine.

ive neen running the engine with that exhaust throttle.. and i forgot how loud it is unrestricted.. my ears are ringing.

Its nice,keep tinkering around with it and you`ll get it. Like I said before and you mentioned just now,toss a simple throttle ring on to restrict the exhust in tandem with your new intake device and it should even out the imbalance you are getting now.

Thanks, i will play with it again tomorrow, its getting late.. and i dont want to anger the neighbors.

I got a few things in mind to try, including improving the venturi effect, i drilled the hole in the barrel kinda wonky, i will fill it and redrill, will also try an exhaust ring... i may even have one laying around... form my one piece throttle experiments.

Here are 2 videos... vid 0032, had the best throttle response, but was running quite lean.

Im happy the engine even runs with it...

As can be seen throttle response leaves alot to be desired, its got me thinking.. maybe its not getting enough air as mentioned, the exhaust throttle works much better, and response is instantaneous.

Have to play with it, its got me thinking it could be improved.

Any more tips?

Re drilled the body today, for a slightly bigger hole, throttle response improved greatly, needle setting are 4 1/2 to start, then turned in 1 1/2 turns as after the engine warms up, also took it apart and took out 2.5mm in height and re soldered it, much better looking now, and less chance of a prop strike.

Had time for a quick test run, as i finished late, and forgot to refuel... so video is short.. will get a longer one in the next few days.

The trailing edge of the prop is chipped after a prop strike on the brass control horn yesterday.. another reason for making it more compact.

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your making me anxious mx

am still waiting for my other engines to arrive from jared, so i can start to work on my throttle again.
from memory i got to about where you are at now when i shelved it.
throttle response good when tuned for low speed, but really needed to do more work to make everything work through the entire rev range.

bernie/ matt/ mx
the thread for the venturi, 1/8 40tpi? what thread form?? bsw unf unc? other?

ado1974 wrote:your making me anxious mx

am still waiting for my other engines to arrive from jared, so i can start to work on my throttle again.
from memory i got to about where you are at now when i shelved it.
throttle response good when tuned for low speed, but really needed to do more work to make everything work through the entire rev range.

bernie/ matt/ mx
the thread for the venturi, 1/8 40tpi? what thread form?? bsw unf unc? other?

I could be wrong Ad's, but I think Cox threads are all
UNC.

want to make sure if possible

i am thinking i will draw a throttle assy in 3d cad, and get it printed in nylon.

was going to try printing the thread, or cutting it with a die, and fit a locknut... havent decided yet.
either way... where is my engines

cheers
a

ado1974 wrote:your making me anxious mx

am still waiting for my other engines to arrive from jared, so i can start to work on my throttle again.
from memory i got to about where you are at now when i shelved it.
throttle response good when tuned for low speed, but really needed to do more work to make everything work through the entire rev range.

bernie/ matt/ mx
the thread for the venturi, 1/8 40tpi? what thread form?? bsw unf unc? other?

I was informed by Matt, in the other thread, its 0.125-40, im not familiar with any of these sizes, i being helped trying to locate one.


Here is a 3 minute video i shot today, running a bit rich.. so it sputters a bit as it burns of the fuel, the needle was out 3 1/4 turns, any leaner than 3 turns and it dies out at full rpm, could be adjusted on the radio but then you are loosing quite a few thou on the top.

A slightly bigger venturi bore, would probably make it perfect. But i dont have a bit thats the right size, and i dont want to ruin it.

It did not like the throttle ring... i have to play around with it some more, it also doesn't like the bigger 020 prop, it will run with it.. but almost no throttle, same results as the mf exhaust throttle copy.

Im very happy with it, it could definitely be flown it the way its, just takes a minute to adjust the settings, a quick top off on the tank, and its ready to go.

In my opinion, its a successful throttle device , im quite impressed with the performance for something so crude and simple.


I think i may try the aluminum soldering stuff on clean pop can aluminum... been needing to build an external tank for my guillows cessna im building... i was worried about brass and tin.. since they seem to corrode from the nitro in the fuel.. while aluminum is perfect... should be very light too

Question for you folks...

Higher nitro content will increase combustion temp correct? i still haven't received my fuel.. so i cancelled my order

Ive been running one year old 20% rc car fuel, (odonell racing fuel) with extra 25% drug store castor, and it still works pretty well considering i kept it in my bathroom for the whole time with the cap not tightly sealed, it could have absorbed some water, the engine runs much better with a glow driver attached, and can burn the fuel off immediately, im thinking with better fuel, higher nitro content = higher temps = better combustion= better throttle response and more power... Am i thinking along the correct lines here?


Thanks

>I was informed by Matt, in the other thread, its 0.125-40, im not familiar with any of these sizes, i being helped trying to locate one.
>
The 5-40 is a standard UNC thread. Taps and dies are readily available from any industrial supply. Check MSC for example for a wide assortment.
Al