rdubord

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

Konrad

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

mike109

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

DarZeelon

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.

Konrad

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

w8ye

My Feedback: (16)

You canot be expermenting with MDS parts for there are no spars to be had!!!

Konrad

Good point. Then the MDS (MAC) line of engines is effectively just a collectors item.
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.

earlwb

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.

tadawson

MDS seems to think that they are alive and well:

http://mds-engines.ru/eng/index.shtml

The fact that the US distributor bailed in another issue altogether . . .

- Tim

Hobbsy

My Feedback: (102)

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.

earlwb

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.

CLBetten

My Feedback: (16)

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.

Hobbsy

My Feedback: (102)

CL, I had a .78 for a while, it was a sweetheart of an engine, about as strong as a good .91 and totally reliable.

CLBetten

My Feedback: (16)

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

Hobbsy

My Feedback: (102)

Yes, it was big with a baffle at the muffler joint and not too loud.

w8ye

My Feedback: (16)

I was thinking I traded you a 48, 58, and 68?

Mr Cox

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...

fiery

My Feedback: (2)

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

Mr Cox

But ripmax is just a retailer aren't they, I mean where could one actually buy these parts?

CLBetten

My Feedback: (16)

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.

Roo Man

My Feedback: (1)

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

w8ye

My Feedback: (16)

I had a MDS 68 for about 5 years and it was a real sweet heart

CLBetten

My Feedback: (16)

Is the .68 ringed? If so you should be able to rebuild any wear related components.

w8ye

My Feedback: (16)

I cannot remember as I traded mine off about 6 years ago.

Hobbsy

My Feedback: (102)

The .68 is ABC, the .78 is the smallest ringed MDS, my sole MDS is a well worn .58.