Hi.

I know MDS engines are criticized often, but I have had good luck with mine. Until recently, the only problem I had with my MDS 40 was that there was hestitation during transition from low-end to high-end RPM.

Then one day it started to just lose power when throttling up and maintaining high RPM - it would either lose power or stall out. It seemed like an air leak. A couple other guys at the club took a quick look at it as well, and we didn't see any air bubbles in the fuel line or anything obvious. For the time being, I richened the high speed needle valve and that helped a little. Then I remembered a fellow club member talking about RC glow cars at one of our meetings and he mentioned an o-ring lubricant/sealant that's commonly used on cars that corrected carb air leaks. He did say it could be used on planes as well.

I went to the LHS and they had a brand called "Green Slime". It was located in the RC cars section, not in the planes section of the store.

MOD #1 - I pulled the C2 carb off the engine and there are 2 o-rings - one at the top of the venturi, and one in a groove toward the bottom of the venturi. I cleaned everything up with alcohol, replaced the top o-ring (original one look good, but I replaced it anyway), put the Green Slime on both o-rings, and installed the carb back on the engine.

MOD #2 - I remember reading a magazine article about glow plugs and one of the things mentioned was to use a glow plug with an idle bar to help prevent the glow plug from getting 'drowned out' after idling for a bit then throttling up. I installed a FOX glow plug with an idle bar.

Let me tell you, this engine transitions MUCH better than it ever has and seems to have more overall power and consistent performance!

I thought this may help some MDS owners out there.

WDWings

i have a .68 MDS that i bought brand new for $50 cause the LHS wanted to get rid of 'em since since Horizon dropped them...i just wanted to know what %fuel you use to break in and what you use now

Hi Tukkus. I have used 10% nitro since day one.

ok thanx wdwings

I bought used MDS 68 off ebay and had it sitting on the shelf waiting till the day comes.
Well,i ended up selling it to a briend of mine for his tower 60 trainer.
Couple days ago we fired it up and MANNN OR MANNN I TELL YA!Thats one hell of a powerhouse.
I taxied through the tall grass half throttle like a bullet,then pulled up and it just wanted to torque roll on the left.So i leveled,trimmed and idled back.Believe it or not i flew the 60 size trainer just two or three clicks above an idle
I am very happy with MDS 68<-thats the bottom line.

Cheers.

Mitty

Troublesome MDS 40s needs to have their bearings tapped out of the case and reset. Put the rear bearing onto the crank while the bearing is still hot from disassembly then reheat the case and slide the crank back in and put the front bearing in. While still hot install the prop collar and a strong plastic prop and tighten it down making the crank very free turning. Transition problems disappear and needle adjustment becomes much easier. Apparently the tolerances are loose enough in the bearings to allow some small misalignment which kills performance. Even so don't overprop it because it likes higher rpms and use an idle bar plug.

I know I'm digging up an old thread here, but....

Does all this apply to the MDS .38 as well, or just the .40's?

Thanks,
Bryan