Returning after a 20 year absence!

[Rogeo1983]

Hi all,

So an update. I have charged the batteries for both tranceivers and the one pack of batteries for the receives, and they all work, so I have ordered new batteries for all today.

I have not even looked at the MDS 40 engine, it is still in the model, which will require some surgery to remove. I am first working on the SC 40. The model is a yamamoto 1600. Purchased new in 1998. The model will require some work to cover the wing, new bands, pushrods fixed for controls, and the throttle cable replaced.

The engine is free now, and surprisingly, turns very free, with good compression. the bearings were really good, very smooth.

The issue is the carb. It is completely frozen. I have soaked it now for 4 days in nitro, cleaned, heated, but nothing will make it turn. If I can buy a replacement carb I will use it, but there are a few engines for sale online, I might just buy one and use mine for parts.

Anyone got any ideas regarding the carb?

In relation to the club, I am based in Ireland, and I have made contact with the local club. I will be meeting up with them once the lockdown is over.

 

the other model is a basic trainer, with wooden box fuselage, and covered with the shrink plastic (cant remember the name Im afraid, its been a while!)

But I had started to make this into a cub replica, so I may use its engine in the main fibreglass model initially, and work on that model over the winter.

Thanks again for all the help, I feel like I am reliving my youth again with this project!

 

I just need to get back and learn to fly again!

cheers

Edited By Rogeo1983 on 19/06/2020 00:20:56

[Keith Miles 2]

Rogeo1983,

Perhaps you could post a picture of the carb? Will it not dismantle? Does it have a screw which holds the throttle barrel in place?

As you may know, O.S. and Saito are about the only manufacturers left producing glo engines and Saito are all 4-strokes, I believe. The trend now, sadly (in my view, anyway) is electric or petrol. A new O.S. 46. 2-stroke will cost you about £120!

There will be second hand SC stuff, and maybe some spares available but tracking down what you want might be an issue requiring time and effort. As you say, it might be worth buying a complete used engine, assuming it isn’t knackered or unless the carb is okay! I believe that SC, ASP and Magnum were pretty much the same engine produced in different Chinese factories! “Just Engines” in Shaftesbury might be able to help as they were once ASP importers.

About ten years ago I, like you, had been out of the hobby for a long time with old gear that I was reluctant to ditch but first, I had to replace tired and unreliable engines for new ones and after about 12 months I decided to replace the radio gear as well. You can probably pick up a modern entry level but much more capable 2.4 GHz computerised Tx and Rx combo, new, for about £100 or less and standard servos for about £8 upwards, each. Electronics has never been so cheap for what you get.

Just something to think about unless, for you, the tinkering is part of the interest, and that’s perfectly fine.

[Rogeo1983]

Hi Keith,

Yes tinkering and building is really what i find interesting. Myself and my son are in the garage daily trying to fix the engine. I think I will just buy a second hand engine, and use mine for parts. Its a cheap alternative.

 

The carb is held in by a screw, this has been removed, in fact I have stripped it completely, but the inner barrel will not budge.

I have just spoken to the local club, and yes I will be only one of a few using 35mhz equipment, but they still have the peg board, so it shouldnt be a problem.

Im just starting to trace parts now, so hopefully I can get it built again soon.

Cheers

Edit:

In relation to my past experience, I was registered, trained and checked out to fly in the main club here. My model was registered with its own tail numbers which were required to be attached with stickers on the fuselage and the underside of the wings. 

I was pretty competent, not in any aerobatics, but just basic safe flying in the circuit.

I will be getting one of the trainers to checkout, test and fly my model first, as is a requirement in the club. My 6 channel tx has a buddy cable, and they still have a simiar tx they can use to buddy to mine and train me. The instructor I spoke to was very excited to be able to get out is old gear to use with me!

Edited By Rogeo1983 on 19/06/2020 09:52:54

[Rogeo1983]

Hi, quick update.

i have just bought a second hand engine to replace this one, I can use the parts from mine if I need spares.

i bought all the batteries, and misc parts I need to get the model fixed up. I just need to buy some covering film to tidy up the wings, so once they all arrive I’ll get this model going.

in the mean time, I have just ordered a cable and software for a sim, so at least I can get my hand back to flying again, and hopefully my son will learn to fly.

i have another model which is a really basic trainer, it will need a bit of work to finish off, but I will build this for my son if he is still interested in a few weeks!

i can’t thank you all enough for the help, back when I was flying these, it was only very small clubs that would be able to help, but now here, having the huge and varied experience is amazing to have, so thank you all again for your help.

[Keith Miles 2]

Glad to hear that you sourced an engine. I did see one or two on E-bay!

Not sure what the situation is with your local club at the moment but ours has had to suspend training temporarily due to the Coronavirus restrictions and pilots flying being reduced from 6 at a time to just 2 to maintain “social distancing”! We’re also only permitted to handle our own equipment not others (oo-er Missus!). Not sure if disposable gloves are allowed! The clubhouse, kitchen, workshop and toilets are currently locked up as are the model benches!

At least we can still fly!

[Rogeo1983]

Hi Keith,

yes the local club club is also closed down, however they have me penciled in when they get back. I am hoping to get set up with a simulator to fly through my tx, so hopefully I’ll get some level of practice in.

in the mean time, I’ll get the models set up, and test run on the ground, and keep flying on the sim!

one of the instructors said he will take my model and test it for me, so it should be ready for my over controlling fingers!

[Frank Skilbeck]

Re the carb, if you know anybody with an ultrasonic cleaner then that would be worth a go. I am surprised though that is so locked up that soaking and heating won't free it off.

[Rogeo1983]

Hi all,

I had the carb put through a cleaner, heated it and it freed up. But as soon as it cooled it seized again. Ill use the new engine, and keep that one for parts.

The other engine freed up nicely, and is rebuilt. New batteries arrived, wiring sorted, so now I just need to get some materials to finish the control rods, and a bit of covering, and Ill be ready to test.

So far so good, Ill post some pics when its done!

Thanks again for all the help.

Regards

[Keith Miles 2]

Posted by Rogeo1983 on 29/06/2020 23:25:57

I had the carb put through a cleaner, heated it and it freed up. But as soon as it cooled it seized again. Ill use the new engine, and keep that one for parts.

That is very, very strange!

I gather, from your previous posts, that you used this engine in the past and that, presumably, it was previously okay? Carb barrels are not usually such close tolerance items and I’ve never heard of barrel expansion or shrinking manifolds! Ruling out corrosion, the only other thing I can think of is ovality in the manifold or barrel but unless you know somebody with the relevant measuring equipment, it might have to remain a mystery!

Would love to know, though!

Good luck with the rest of your project(s)!

[Rogeo1983]

Hi all,

Quick update.

Finally parts ordered, i should have Nitro, solarfilm, a fuel pump, bands, balsa for the ailerons and wing tips, and i received yesterday the sc 40 engine. So im good to go. the local flying club is still under a restriction, but i have an instructor who is going to test fly the model for me, and get it set up.

So the 1st model will be ready for test flight this week. Its a yamamoto 1600, sc40 35mhz sanwa. I just need to install the engine and fuel tank, cover a small part of the wing, and refix the control surfaces using proper hinges. the mylar ones just kept failing off over time.

the second model is a very basic trainer that i was rebuilding into a cub type replica. That needs to be covered totally, new ailerons made and covered, the mds 40 engine fitted, fuel tank, and the servos installed. It is also flown with a sanwa vanguard 4 channel 35mhz tranceiver.

I have just finished the tailplane in a cub style, and the tailwheel has been ordered for delivery tomorrow.

I will update with some more pictures when i get it done.

The cable for the simulator arrived, but it was the wrong type, it was too small, so i am still hunting for that.

Cheers

[Rogeo1983]

here are some photos

[cymaz]

Best of luck with the flying.

[Rogeo1983]

So a bit of work today, All tested except the engine. I still need to replace the hinges with new ones, thats for tomorrow.

So tomorrow i eill be starting the engine for the first time in 20 years. I have new fuel and a new glow plug. I am having trouble finding the initial settings of the high speed needle and the low speed screw. Does anyone have any idea of them? Its for an SC 40.

Here is the pics of the model.

Cheers

[Keith Miles 2]

If your SC40 carb is, as I believe it is, similar to my Irvines, i.e. a non air bleed type with the main needle one side of the carb and idle screw on the opposite side, this is the initial set up procedure that I use and assuming that the throttle arm is correctly positioned. It’s an old tip that I picked up years ago and it has worked for me!

Take a length of fuel tube and attach it to the fuel inlet at the carb.

Open the main needle valve fully.

(Disconnecting the control link from the throttle arm is preferable so that you can easily move and hold it with your finger. Easy if using a clevis. Less easy if you have wire and a z-bend in which case you would need to release at the servo end. Depending on your set up, it might be best here to lift off the output arm from the servo for easier repositioning as I suspect that you have no “travel adjust” facility, more of which later!

Take a 1mm drill or piece of piano wire and use it as a feeler gauge inside the carb manifold in order to set the throttle barrel slightly open. Obviously you need to keep the “gauge” in the centre of the barrel opening!

With the barrel gently clamping the drill/wire, blow into the fuel tube and listen for the “hiss” inside the manifold. (I find it easiest, and more accurate, to stick one end of another piece of fuel tube into the manifold and the other end in my ear as a stethoscope!).

What you are listening, and aiming, for is just a very slight hiss at this setting. Turn the idle screw out to increase the airflow and in to decrease it.

This will give you a fairly accurate initial setting for idle.

Next, turn the main needle in fully and then back it off by the usual 2 - 2 1/2 turns for initial starting.

That done, you can then re-connect the throttle link, if removed, readjusting for full travel as required to achieve full and closed throttle, especially the latter!

A “travel adjust” on a modern Transmitter sure makes setting up throttles much easier! No offence intended!

As for the main needle setting, this will only be determined after starting at the above setting. You will then turn the needle in (which leans the mixture) gradually until the engine note gradually picks up and just  “peaks” into a steady two stroke. If you then raise the nose to about 45 degrees and the engine slows, the engine is too lean and you need to turn the needle out slightly to richen the mixture. 

I assume that you will be fitting a new glo plug. If nothing else it will be one thing to eliminate as a cause for any running problems, bearing in mind the age of the engine!

I hope that all of this helps and that I’m not insulting your intelligence!

Keep us posted!

 

 

Edited By Keith Miles 2 on 15/07/2020 02:51:54

[Denis Watkins]

Very accurate rendition Keith, to retune a motor with unknown needle settings.

[Keith Miles 2]

Posted by Denis Watkins on 15/07/2020 07:49:28:

Very accurate rendition Keith, to retune a motor with unknown needle settings.

Thanks, Denis!

I, perhaps, should, or could, have added that to get final adjustment of the idle screw requires checking for smooth pick up from idle to full throttle, so to cover that, just in case......

After the main needle has been set for full throttle, reduce the throttle to idle for about 15-30 seconds, then open the throttle.

If the engine stutters before increasing speed, idle is too rich. If engine slows before increasing speed, idle is too lean. Turn the idle screw in slightly to lean the idle mixture and out slightly to richen it, then re-test.

Final tick over speed should then be set with the throttle trim on the transmitter and, ideally, with zero trim and minimum throttle stick cutting off the fuel and stopping the engine.

Again, a transmitter with a “throttle cut” as well as a “travel adjust” function also makes life very much simpler and avoids  “faffing” about with control linkages to achieve just the right amount of throw at the carb. I remember it well!

Edited By Keith Miles 2 on 15/07/2020 08:49:39

[Rogeo1983]

hi Keith,

I cant thank you enough for the post, a great and very detailed description.

I have new fuel and a new glow plug. So I will tune the carb first then try to start it.

My plan is to get it set up with a long pushrod by hand for the throttle link to the carb, and once i find the settings, I will connect the servo with the throttle at idle but the trim at full. then I can back off the idle screw and use the trim to cut the engine. It worked for me in the past. Its all coming back to me.

I still need to replace the hinges with better hinges with metal pins, and i think i will replace the ailerons, they are wobbling about a lot. a small bit of covering at the aft trailing edge over the fuselage, and fit the new bands.

Once that is done and the engine is working, Its ready for a test flight. Is it still c of g approx 1/3 back from the leading edge?

Im hoping to get it test flown by a local instructor by the end of the week. Amazingly the model is still registered with the same tail number, so once my insurance cert arrives from the club, Im good to go.

I just need to get the cable for my controller to connect to the computer, so i can get my cashes out of the way in a virtual role!!

thanks again for all of the help.

Regards

[Nigel R]

I'd probably start at 25% of chord for first flights, if I knew nothing else about the model.

[Caveman]

Rogeo, did you see my message on 13th July on your simulator thread ref the cable for your computer?

GDB

[Keith Miles 2]

Posted by Rogeo1983 on 15/07/2020 12:41:59:

hi Keith,

 

I cant thank you enough for the post, a great and very detailed description.

I have new fuel and a new glow plug. So I will tune the carb first then try to start it.

My plan is to get it set up with a long pushrod by hand for the throttle link to the carb, and once i find the settings, I will connect the servo with the throttle at idle but the trim at full. then I can back off the idle screw and use the trim to cut the engine. It worked for me in the past. Its all coming back to me.

“Back off the idle screw”?

Are you, perhaps, confusing a “throttle stop” screw with an idle screw? 

DO NOT treat the idle screw/ low speed screw as a primary means of setting the final idle speed!

It is there, primarily, for setting the idle (low speed) fuel/air MIXTURE, initially with the throttle barrel at a rough idle position as described (i.e. slightly open) and is then used to fine tune the throttle response from low to high, again, as described.

After the idle MIXTURE screw is set and the throttle operates smoothly from low to high, LEAVE IT ALONE!

Final tick over speed is largely determined by setting the correct amount of throttle barrel opening i.e. by adjusting the cable or pushrod linkage between servo and throttle arm and by using the trim on the transmitter, as required.

(Unless, without rubbing it in, you have a modern radio!)

 

On the C.G. issue, on that type of aircraft, I would start with it just ahead of the thickest part of the wing which will probably equate to about 25 - 30% back from the leading edge.

Edited By Keith Miles 2 on 15/07/2020 20:15:47

[Rogeo1983]

Hi Caveman,

yes i did, Ive tried to contact that company you mentioned, but i havnt received a reply yet, ill try again tm. I have two other suppliers at the moment checking if it will fit. Thanks for your help.

Hi Keith, perhaps i am. Now that you mentioned it, i was wondering how that screw changed the Idle mix.

So it did actually start, but my glow battery (also 20 years old) failed. New one ordered.

So i have the pictures here, will you tell me which one you are talking about? Now i am thinking that the idle mix is the one at the side, eg straight into the barrel of the carb, the idle stop screw is on top of the housing, and the high speed needle is on the side above.

I will strip it out again tm and start again. Thank you for your paitence, an help!!

Do I have this right?

Thanking you in advance

[Keith Miles 2]

Rogeo1983,

Yes, I’m talking about the two mixture screws, idle (low speed) and main (high speed), NOT the throttle/idle stop screw.

All that the throttle/idle stop screw does is stop the throttle barrel falling out and it also limits the amount by which the throttle barrel can rotate towards the closed position, hence the “stop”. In other words it is purely a mechanical function and nothing to do with mixture setting.

So all you really need to do is screw it in enough to hold the barrel in place and to allow the barrel to rotate to a closed position without binding the servo. The more that you screw it in, the less the barrel will be able to rotate in the closing direction. Try it and you’ll see what I mean.

Bear in mind that the idea of the 1mm drill and “ hiss” technique is to initially achieve a rough normal idle position for the throttle barrel and a corresponding rough simulation of required fuel flow at that position.

So, what you can possibly do is screw in the throttle/idle stop screw to help you to set the 1mm gap whilst you adjust the idle screw during the “hiss” test. Once you have an initial setting for the idle mixture screw, you can then unscrew the throttle/idle stop screw sufficiently to allow the barrel to rotate to the closed position or even beyond closed, but not so much that the barrel is no longer held in place! The spring on the screw is to hold its position and prevent the screw from working loose due to vibration!

Obviously, if you leave the throttle/idle stop screw set for idle when you have the engine running, you won’t be able to stop it by closing the throttle manually or on the transmitter and you might also put strain on the servo if the link has been set up for full closure! Other methods of stopping an engine are best avoided!

This is also why modern radios are so useful for setting up throttles because they allow you to not only fine “trim” the initial servo output arm position but also to fully adjust the amount of servo movement in each direction either side of centre. It allows you to much more easily get exactly the amount of movement required to achieve full and closed throttle or full, idle and a button or switch for throttle cut-off. No need to faff about experimenting with different holes on the servo and throttle arms, adjusting clevises etc. etc.

So, to recap, the “stop” screw has nothing to do with adjusting the fuel/air mixture. It merely positions the throttle barrel.

The idle screw sets idle/low speed fuel flow.

The main screw sets high speed fuel flow.

Air flow is determined by barrel position and fuel/air mix is achieved by a combination of the rotational (for air) and sideways (for fuel) movement of the throttle barrel as the throttle is operated.

Don’t be afraid to ask if you need any further clarification or help!

 

Edited By Keith Miles 2 on 16/07/2020 02:15:40

[Nigel R]

Rogeo

The OS engines always come with an excellent guide to setting up a twin needle carb from scratch.

See:

OS engine manual

Page 17 onward.

There is one main difference from your engine, the OS motor in that manual has the full speed needle mounted at the back of the engine, but, it operates the same way as your main needle, ie clockwise to make lean.

Page 20 / 21 has the main needle adjustment routine.

Page 22 has an excellent idle adjustment chart. Note OS call the idle mixture screw the "mixture control valve".

Keith's posts above are also excellent info.

[Keith Miles 2]

Rogeo1983,

Excellent tip from Nigel but bear in mind that the advice given for re-setting the initial position for the idle/low speed mixture screw applies specifically to the OS engines whereas the initial set up method I described will work with ANY “twin needle” type of carburettor.

It is worth repeating that once you have the idle mixture screw set to give you a smooth throttle response from idle to full throttle without the engine “stuttering” (too rich) or slowing (too lean) as you open the throttle, leave it alone! Any subsequent adjustment should only need to be made with the main needle and with the engine at full throttle and then, preferably, checked by raising the nose of the aircraft to ensure that it is not set too lean. Obviously, it is safest, especially with a large model, if you have another pair of hands to assist here, one pair for the model and one for the transmitter!

Don’t forget, of course, all of the usual safety considerations and precautions to avoid injury!

If you go to the top of this page and click on “Features/Engines/Go Glow”, you will also find an excellent article by Alex Whitaker. Well worth an additional read if your memory needs refreshing!

Edited By Keith Miles 2 on 16/07/2020 11:37:06

[Rogeo1983]

Hi Nigel,

yes i have had to replace the carb due to mine not working. The original rear mounted needle is bypassed, and the fuel line goes straight to the front carb mounted high speed mixture screw. I didnt have shorted srews to replace the rear mounted bracket. Thanks for the link to the manual, mine went walkabouts years ago.

Hi Keith,

Thanks again for your help. I did run the engine yesterday for a few mins, it ran really well, i had forgotten how much of a mess that these little engines make!!

I am going to strip the cowl again today and tune the carb as per your instructions, and start again. I am still waiting for a new glow battery, so ill crack on with that.

Ill report back once i have some progress.

Cheers, and thanks again