Carb tuning

[Charlie Whittaker]

Hi I am new to the page and new to the nitro plane hobby (I’ve had never nitro cars before but no planes

I have recently bought a free flow drainpipe special with a mds 40 nitro engine in it, it is running very poorly (I will attach a video) please could someone put me in the right direction of tuning thank you

[Denis Watkins]

Charlie, read Keith Miles tuning explanation at the bottom of this page

The blowing down the feed tube works for other makes too

**LINK**

Edited By Denis Watkins on 22/07/2020 18:21:48

[Martin Harris - Moderator]

Hopefully we'll get to see the video soon (easiest to upload it to YouTube and link to it). MDS engines don't have a great reputation although good ones run very well once sorted.

In the mean time, a few details like what fuel you're running on, glowplug and propeller size used may help us to advise you.

[Jon H]

Yeaa MDS...stands for 'many dead sticks'.

Sadly their carbs were pants and its rare you can get one to actually work. A carb swap can really help and justengines might be able to help you with that.

As martin rightly suggests though, a run down of the prop, fuel, plug etc would really help eliminate potential issues.

[Martin Harris - Moderator]

Mine Don't Stop - but I think the 38 and 58 that I still drag out on occasions may have a better reputation than some of the other models. Over the last several years, the 38 has only been used in temperatures around freezing as it lives in my venerable Limbo Dancer fitted with oversized floats that I fly when we have snow on the ground...the floats do make for some rather interesting handling in the air!

Any luck with that video, Charlie?

Edited By Martin Harris on 22/07/2020 22:12:19

[Richard Wills 2]

I am playing with an old Robbe MDS 40 at the moment, as has been said previously the carb isn't the best. I have got it to run well now even though it leaks fuel like a tap from both needles despite new orings. A bit of nitro seems to mask the inaccurate carburation 10% has done the trick and making sure both needles are set properly is important if at all over rich it'll cough and splutter itself to death. Is it a used plane? If so eliminate any other problems by rebuilding your tank, replace all fuel pipes and fit a new plug before you start on the engine tuning.

[Richard Clark 2]

Posted by Charlie Whittaker on 22/07/2020 17:28:39:

Hi I am new to the page and new to the nitro plane hobby (I’ve had never nitro cars before but no planes

I have recently bought a free flow drainpipe special with a mds 40 nitro engine in it, it is running very poorly (I will attach a video) please could someone put me in the right direction of tuning thank you

 

 

Further to Martin's, Jon's, and Richard's comments I would like to add that none of these cheap OS 'clones' seem to be much good. But unfortunately OS prices have now become nonsensical.

I had an SC 60 where the carb was so leaky, both for air and fuel, that it wouldn't stop when the throttle was totally closed.

However, here's  how to adjust the throttle:

1) Full throttle is easy. Run it flat out, slowly screwing the 'main needle' in until the engine reaches full power. Wait a bit each tine until it 'settles down'. If it stops open the needle a few clicks and try again.

Having got it running ok hold the plane vertically nose up and if it stops open the needle a few more clicks and try again.

2) Back to horizontal. Close the throttle, leave it for a few seconds and suddenly open it. If it stops 'cleanly' open the 'idle' needle a bit and try again. If it pops and splutters with lots of smoke it's too rich so close the idle needle a bit and try again.

3) You may then have to go back to 1 and make a small adjustment to the main needle.

4) Having got it right DON'T constantly fiddle with it on the field to try and make it 'better'. Such 'further adjustments' should nor be needed often, if at all, unless you are at opposite extremes of temperature.

5) 'Nitro'. Despite what some people call the fuel engines don't run on 'nitro'. it it is just a small and optional additive. Just a few percent at most , Zero, 5% or 10% is the norm. 5% may improve the idling slightly. 10% gives marginally improved 'top end' performance but is hardly worth the extra cost..

Edited By Richard Clark 2 on 23/07/2020 07:28:19

[Jon H]

Richard im in agreement apart from the nose up test. Its just a complete waste of time, not at all representative of in flight conditions and only leads to engines running excessively rich. I dont know how or why this pointless exercise has endured over the years but there we are.

Beyond that, yep all sounds good although i always recommend checking the main needle at the start of every flying session. By that i mean 5 seconds to tweak it back/fwd to make sure its right and not half hour before every flight revving the thing and waving it around in the air.

[Richard Clark 2]

Posted by Jon - Laser Engines on 23/07/2020 08:12:38:

Richard im in agreement apart from the nose up test. Its just a complete waste of time, not at all representative of in flight conditions and only leads to engines running excessively rich. I dont know how or why this pointless exercise has endured over the years but there we are.

Beyond that, yep all sounds good although i always recommend checking the main needle at the start of every flying session. By that i mean 5 seconds to tweak it back/fwd to make sure its right and not half hour before every flight revving the thing and waving it around in the air.

Jon,

Yes, It is probably more of a 'ritual' than anything else. I find myself doing it even on pumped engines

[Nigel R]

"not at all representative of in flight conditions"

I must agree to disagree on this point. When I flew a few days ago, a sustained full throttle vertical was a routine maneuver in all of my flights.

"But unfortunately OS prices have now become nonsensical."

Cobblers, complete and utter, demonstrably so.

I paid around £100 for an OS 61 RF in the early 1990s.

From bank of england figures, £100 is worth £220 today.

Just Engines sell a 55AX for around £150, and a 65AX for £172 - neither are £220.

Let's go back a bit further:

In 1974, an OS 60 FSR was £54 - source: old review of 60 FSR

£10 in 1974 is apparently worth £105 today. That would make the 60 FSR sticker price £567 today.

What we no longer have, is the cheap stuff (Sanye) from assorted low labour cost countries undercutting the market.

[extra slim]

back in the day when I had a MDS 40.. it would only run on a 10x6.. any other prop it just wouldnt behave. Strangest engine I have ever had. Interestingly, many years later chatting to a club member, he had exactly the same issue. Was noisey and not very powerful, but behaved very well on said prop.

[Jon H]

Posted by Nigel R on 23/07/2020 10:09:25:

"not at all representative of in flight conditions"

I must agree to disagree on this point. When I flew a few days ago, a sustained full throttle vertical was a routine maneuver in all of my flights.

But you were moving forward at more than 20mph and that makes all the difference. You never sit there at full throttle while nose high and not moving. That is why i say its not representative of flight conditions.

[Nigel R]

Except for the bit where I was hanging on the prop for a few seconds before kicking over for a stall turn.

Otherwise I agree, the loading on the motor is different; rpm will be increased and required needle setting slightly changed.

[Jon H]

Posted by Nigel R on 23/07/2020 10:32:46:

Except for the bit where I was hanging on the prop for a few seconds before kicking over for a stall turn.

Wont be at full power for that part though

[Martin Harris - Moderator]

Sustained prop hang?

We're in danger of going over old ground again but when I tried Jon's level sustained power check as an experiment it didn't work - I got a deadstick on an otherwise reliable engine. Re-tuned with a nose up, it returned to its old reliable ways.

I would contend that Jon is correct with an ideal tank position but so many ARTFs and plan designs don't make it easy to achieve this. I believe that Jon goes to great trouble to modify his own aircraft to feed his engines with correctly located tanks - something that we would all do well to emulate but the nose up check allows consistent operation with models not so well prepared. For example, I've spent many hours pondering how to lower the fuel tank in the Tempest I'm building and concluded that it really isn't possible to get the tank below the normal tank bay, due to the proximity of the main spar preventing any tank I can find fitting in the gap between it and the carburettor air intakes on the inverted Laser 200v. The compromise is a very low profile tank but I know that this will result in a small fuel head in operation so it will lean out slightly during acceleration/climb and a nose up check will allow me to tune for reliability.

Edited By Martin Harris on 23/07/2020 12:20:26

[Nigel R]

Time for a chicken hopper tank?

[Jon H]

Posted by Martin Harris on 23/07/2020 12:04:13:

Sustained prop hang?

We're in danger of going over old ground again but when I tried Jon's level sustained power check as an experiment it didn't work - I got a deadstick on an otherwise reliable engine. Re-tuned with a nose up, it returned to its old reliable ways.

I would contend that Jon is correct with an ideal tank position but so many ARTFs and plan designs don't make it easy to achieve this. I believe that Jon goes to great trouble to modify his own aircraft to feed his engines with correctly located tanks - something that we would all do well to emulate but the nose up check allows consistent operation with models not so well prepared. For example, I've spent many hours pondering how to lower the fuel tank in the Tempest I'm building and concluded that it really isn't possible to get the tank below the normal tank bay, due to the proximity of the main spar preventing any tank I can find fitting in the gap between it and the carburettor air intakes on the inverted Laser 200v. The compromise is a very low profile tank but I know that this will result in a small fuel head in operation so it will lean out slightly during acceleration/climb and a nose up check will allow me to tune for reliability.

Edited By Martin Harris on 23/07/2020 12:20:26

you dont prop hang at full power

we are getting off track a bit but yea, your problem with the dead stick was likely the fuel tank position. Lower the tank and give it another go. The reason i take the time to make sure the fuel tank is in the right place is that it saves all the guess work when it comes to overall engine operation. It also saves fuel, makes the model cleaner and prolongs the life of the engine as you are not running rich for half your flight so the chance of rust in the crankcase due to accumulated fuel is lower. Seems like a fair reward for a little balsa bashing.

We should probably discuss the tempest elsewhere, but i am surprised to hear there is no room. Typhoons, yea they can be an issue, but the tempest has a half decent nose so it should be ok. If not, just cut new notches in the ribs, beef them up and move the main spar. Overlap it with the current spars by 2 rib bays either side and cut out a bay just large enough for a tank of the required size. you need 20oz tops for a 200 so no gallon buckets needed

[Jon H]

Posted by Nigel R on 23/07/2020 12:57:09:

Time for a chicken hopper tank?

unless pressure isolated overall fuel head remains the same.

There are methods of sorting that, but they introduce their own issues. On balance, its less effort to mod the airframe during the build than fight with it every day you fly.

[gangster]

Please let’s not have the old nose up or not debate again. Whilst I have never owned an MDS I agree it is well understood that the earlier carbs had issue.
Interesting comment suggesting that none of the OS carbs are much good. In my experience they have been perfect.

I moved down the SC /ASP route nearly 20 years ago . I went into my LMS to buy an Irvine 61, for some reason Irvine we’re not making any at the time. My choice was between Super Tigre and OS. The proprietor suggested I also looked at an SC. On his recommendation I bought the SC. What a fabulous engine, swung a bigger prop easily started with a couple of flicks and was so reliable. I have been hooked ever since. Everyone I have had has been perfect This included one I bought on ebay a few years ago for £18 flew it dozens of times with noisy bearings until I replaced them and have had hundreds of flights and never a deadstick

i have to agree about the post that suggests that an OS 60 was £500 plus and of course a basic set of Futaba would have been about £2.5k in real terms. I also think that the way things are going we could well go back to paying considerably more for everything

[Nigel R]

That is its raison d'etre of a chicken hopper.

"you dont prop hang at full power"

Sport model, only just over 1:1 thrust/weight, not a 3d type. "prop hang" was a loose description...

[Richard Clark 2]

Posted by Nigel R on 23/07/2020 10:09:25:

......."But unfortunately OS prices have now become nonsensical."

Cobblers, complete and utter, demonstrably so.

I paid around £100 for an OS 61 RF in the early 1990s.

From bank of england figures, £100 is worth £220 today.

Just Engines sell a 55AX for around £150, and a 65AX for £172 - neither are £220.

Let's go back a bit further:

In 1974, an OS 60 FSR was £54 - source: old review of 60 FSR

£10 in 1974 is apparently worth £105 today. That would make the 60 FSR sticker price £567 today.

What we no longer have, is the cheap stuff (Sanye) from assorted low labour cost countries undercutting the market.

 

Cobblers to you. We are not in 1974..

Today:

OS 72 FSa II £420 (Ripmax - in stock). £379 (Just Engines - not in stock). They can quote any fairy story price they choose for something they haven't got.

Laser 70 £239 including postage (in stock).

That's £181 difference. So not yet started Warbirds Spitfire meet  Laser 70.

 

Edited By Richard Clark 2 on 23/07/2020 15:06:19

[Nigel R]

And you are not talking about OS prices "becoming nonsensical".

[Jon H]

The chap in the OP is probably wishing he never asked..

Gangster, sorry, it just triggers me as no amount of arguing will make the nose up test any less pointless...unless the engine is pumped, then it can be used to help detect pump failure. Counter intuitive huh?

OS prices are...inventive, especially the 4 stroke side. If you want a cheap 2 stroke there are plenty 2nd hand or some new offerings from just engines.

4 stroke you only have Laser and saito to pick from if OS are deemed to expensive.

Richard...i did have stock

[john stones 1 - Moderator]

[Richard Clark 2]

Posted by Nigel R on 23/07/2020 15:09:02:

And you are not talking about OS prices "becoming nonsensical".

I think the UK prices of OS engines have become nonsensical. Obviously I think that or I wouldn't have posted that opinion.

Comparing prices today with past prices is pointless. It's comparisons with today's prices of similar 'good quality' products that matter. Thus my OS/Laser comparison.