MDS 48 mid-range issue
#1
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MDS 48 mid-range issue
I can get the top end tuned in nicely, and then the idle tuned nicely as well. The thing will run both wide open and idle, for as long as the fuel remains in the tank. However, the mid-range is extremely rich. I tried running both the high and low ends on the lean side to compensate, but it wasn't near enough. I found that one of my K & B 40 carbs was close to the same size and installed it. Only got one run in (being neighbor friendly at 8:45pm) and the carb loosened some. During the short run, it was much, much better. I now have the carb mounted better and tight and will run it tomorrow.
Background, I bought this engine back in 2002 brand new and was told that it was the 'newest' MDS 48 with the 'improved' carburetor. Does anyone know of a third 'generation' carb for the 48? Is there any easy mod to lean the mid-range.
Thanks
Background, I bought this engine back in 2002 brand new and was told that it was the 'newest' MDS 48 with the 'improved' carburetor. Does anyone know of a third 'generation' carb for the 48? Is there any easy mod to lean the mid-range.
Thanks
#2
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RE: MDS 48 mid-range issue
What nitro % are you using? And yes it is very easy to rework the low speed needle to get just about any mixture strength you want from a Bodemann style carb (true twin needle carb).
I think there is some detail on how to do this in my carb thread.
All the best,
Konrad
I think there is some detail on how to do this in my carb thread.
All the best,
Konrad
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RE: MDS 48 mid-range issue
G'day
A friend of mine turned up here recently with an MDS 46 which his brother bought new but had only run a few times and never flown. We tried running it and had the same problems you are having. I just happened to have a Super Tigre GS 40 (apart from a head) so I checked to see if the carby would fit the MDS and it did. The result was a very sweet running engine and it is very easy to tune now. We were running 10% nitro because that was the only fuel I had at the time.
One possible solution.
Hope this helps a little.
Mike in Oz
A friend of mine turned up here recently with an MDS 46 which his brother bought new but had only run a few times and never flown. We tried running it and had the same problems you are having. I just happened to have a Super Tigre GS 40 (apart from a head) so I checked to see if the carby would fit the MDS and it did. The result was a very sweet running engine and it is very easy to tune now. We were running 10% nitro because that was the only fuel I had at the time.
One possible solution.
Hope this helps a little.
Mike in Oz
#4
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RE: MDS 48 mid-range issue
Many, many carburettors on model engines, do not meter the fuel properly...
Among them are the older MVVS, many from OS, older Rossi and others.
The top-end and the idle can be set perfectly; and the transition from idle will be nearly perfect.
But if after you set the high-end and the idle perfectly, you try to run the engine in any part-throttle position; the mixture will be way too rich.
And after running at that setting; even for just a few seconds, transition to full-power; as well as down to idle, will be lousy...
It may even cause the engine to conk-out.
Enough fuel would have accumulated in the crankcase, to prevent a smooth pick-up, or drop down.
Trying to 'twiddle' the needles will get you nowhere flat...
A different setting that will make the mid-range leaner/better, will necessarily make the idle mixture too lean...
If this problem is encountered, a master can 'recurve' the low-speed needle's taper, to allow it to be closed further; leaning the mid-range, without causing the engine to lean-out at idle. Some manufacturers (MVVS) sell needle-nozzle sets to get this effect.
For anyone else, a better replacement carburettor is in order.
I can recommend those made by Perry, Super-Tigre, the new MVVS, the new Rossi and Enya.
Some will need to be made to fit the target engine.
Among them are the older MVVS, many from OS, older Rossi and others.
The top-end and the idle can be set perfectly; and the transition from idle will be nearly perfect.
But if after you set the high-end and the idle perfectly, you try to run the engine in any part-throttle position; the mixture will be way too rich.
And after running at that setting; even for just a few seconds, transition to full-power; as well as down to idle, will be lousy...
It may even cause the engine to conk-out.
Enough fuel would have accumulated in the crankcase, to prevent a smooth pick-up, or drop down.
Trying to 'twiddle' the needles will get you nowhere flat...
A different setting that will make the mid-range leaner/better, will necessarily make the idle mixture too lean...
If this problem is encountered, a master can 'recurve' the low-speed needle's taper, to allow it to be closed further; leaning the mid-range, without causing the engine to lean-out at idle. Some manufacturers (MVVS) sell needle-nozzle sets to get this effect.
For anyone else, a better replacement carburettor is in order.
I can recommend those made by Perry, Super-Tigre, the new MVVS, the new Rossi and Enya.
Some will need to be made to fit the target engine.
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RE: MDS 48 mid-range issue
As most low speed needles are rather an inexpensive parts. One can experiment a bit with little impact on the pocket book, should one mess up.
All the best,
Konrad
All the best,
Konrad
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RE: MDS 48 mid-range issue
ORIGINAL: w8ye
You cannot be expermenting with MDS parts for there are no spars to be had!!!
You cannot be expermenting with MDS parts for there are no spars to be had!!!
This doesn't negate the fact that one can easily modify the low speed needle to custom tailer the fuel delivery. Maybe one could practice this on a twin needle carb that is still in production prior to tackling the MDS.
I do think that most of the tuning issues can be addressed with the proper fuel and glow plug.
#8
RE: MDS 48 mid-range issue
I would suggest using a better carb. The Russian carbs were not all that great. But sometimes you got lucky and got a decent carb with the engine.
I just replaced a carb on a Russian/Soviet engine I was playing with earlier. In that case you could not lean out the idle mixture at all on the carb so the engine only had engine stop, 3/4 throttle to WOT, but no idle and no in between.
But now the carbs aren't all that cheap and can be quite expensive in some brands, so then one has to determine whether it is worth it or not. it helps to have accumulated extra things like carbs over the years, so you don't have to buy a new one you just rummage through your old parts boxes for something to use.
I just replaced a carb on a Russian/Soviet engine I was playing with earlier. In that case you could not lean out the idle mixture at all on the carb so the engine only had engine stop, 3/4 throttle to WOT, but no idle and no in between.
But now the carbs aren't all that cheap and can be quite expensive in some brands, so then one has to determine whether it is worth it or not. it helps to have accumulated extra things like carbs over the years, so you don't have to buy a new one you just rummage through your old parts boxes for something to use.
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RE: MDS 48 mid-range issue
ORIGINAL: w8ye
You canot be expermenting with MDS parts for there are no spars to be had!!!
You canot be expermenting with MDS parts for there are no spars to be had!!!
http://mds-engines.ru/eng/index.shtml
The fact that the US distributor bailed in another issue altogether . . .
- Tim
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RE: MDS 48 mid-range issue
Earl, if I could hazard a guess, I'd say that somebody turned the LS needle in too far. The MDS LS needle has a blunt taper and if leaned too far will bellmouth the end of the spraybear. Then you get exactly what has been described here. When set in the ideal position the LS needle will be about 1/32nd" from the end of the spraybar at full throttle.
#11
RE: MDS 48 mid-range issue
I am going to look at the carb again later.
I had swapped it out for a old OS 7B carb I happened to have extra. The engine ran really well off the OS carb. So i had put the MDS carb up and didn't bother with it after that.
I'll take a look and see if I can get it apart and see if maybe I can swage the tip back down a little or not. I don't mind messing with something that doesn't work already.
I had swapped it out for a old OS 7B carb I happened to have extra. The engine ran really well off the OS carb. So i had put the MDS carb up and didn't bother with it after that.
I'll take a look and see if I can get it apart and see if maybe I can swage the tip back down a little or not. I don't mind messing with something that doesn't work already.
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RE: MDS 48 mid-range issue
I would be happy to see MDS reappear in the U.S. market. I would like to check out one of the .78 sized ringed engines. I had a very early .40 that threw a rod but the factory was completely willing to make good on it. With factory upgraded parts it was a fine engine.
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RE: MDS 48 mid-range issue
I had no problems with tuning my carburator. That was the first rc engine I ever owned on my first plane. I cut the muffler in half on my .40 removed the baffle and then TIG welded it so you couldn't tell I had modified it. That really seemed to wake it up. Sadly the MDS were rejected off-hand around here. Were you running the stock muffler on your .78 ?
Take care, Cliff
Take care, Cliff
#16
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RE: MDS 48 mid-range issue
ORIGINAL: CLBetten
I had no problems with tuning my carburator. That was the first rc engine I ever owned on my first plane. I cut the muffler in half on my .40 removed the baffle and then TIG welded it so you couldn't tell I had modified it. That really seemed to wake it up. Sadly the MDS were rejected off-hand around here. Were you running the stock muffler on your .78 ?
Take care, Cliff
I had no problems with tuning my carburator. That was the first rc engine I ever owned on my first plane. I cut the muffler in half on my .40 removed the baffle and then TIG welded it so you couldn't tell I had modified it. That really seemed to wake it up. Sadly the MDS were rejected off-hand around here. Were you running the stock muffler on your .78 ?
Take care, Cliff
#17
RE: MDS 48 mid-range issue
I don't know much about the larger sizes but on the smaller .17 and .18 the muffler is really too restrictive and that also affects the tuning of the carb. The hole distance on the mufflers of the .17 and .18 are the same as for OS and ASP etc. So that is another thing to swap around that really improves the high end.
The fact that there is still a website (dated 2009) doesn't mean that they are still being made...
The fact that there is still a website (dated 2009) doesn't mean that they are still being made...
#18
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RE: MDS 48 mid-range issue
Ripmax (A large UK Model Supplies distributor) were offering retailers MDS Engines as their house brand (RMX) up until recently. They had been updated and re-designed from those sold in the 'States. The RMX engines seem to have disappeared as well.
http://www.google.com.au/imgres?imgu...w=1276&bih=599
Ripmax only seem to stock MDS spare parts now
http://www2.ripmax.net/3index.asp?Pa...r=3&Search=MDS
http://www.google.com.au/imgres?imgu...w=1276&bih=599
Ripmax only seem to stock MDS spare parts now
http://www2.ripmax.net/3index.asp?Pa...r=3&Search=MDS
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RE: MDS 48 mid-range issue
I wouldn't bet my life savings ($14.83) but I don't think I got any MDS engines from you. I have only had the .40 and helped a guy with his .48. We put a tuned pipe on the .48. If I remember correctly it had a black head.
#21
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RE: MDS 48 mid-range issue
I recently purchased an almost new 60 size Twist that has a MDS 68. When I found out thart the engines/parts were no longer available I was very upset with the shop owner for not telling me. I have mostly forgiven him because the engines runs like a dream, is very strong and tunes well. It appears to be one of the last MDS engine designs with a great carb and alot of power. Very reliable. Guess I have to hope it is also long lived.
I have sent several e-mails to the mfg. without qany reply.
Gary
I have sent several e-mails to the mfg. without qany reply.
Gary