stearman70

Hello. I have a .48 glow 2 stroke MDS engine. I bought it used but it feels good compression and looks like new. They sold it because it didn't develop in high speed. He's got a very good ralentí speed. I've tried everything so I can carburete it, but it shuts down high. I've done all the possible combinations with the 2 squeezing, but it's off high. Low works very well. Will he be haunted? For 50 years I use 10% nitro and do not think the solution is to increase it to 15% nitro. What's your suggestion. Thank you in advance.

A. J. Clark

Some questions to help answer your question. What size prop are you useing? Are you running the engine on a test stand or mounted to a plane? Where is the center line of the fuel tank with relationship to the carb inlet? What does the glow plug element look like? Does the glow plug have a good glow with the igniter on it?

skorz

I personnaly own a mds61, not the most powerfull engine but runs good with a 12x6 ( usually used for a good 45....)

The cylinder head is may be not dissipating enought compare to others brands, or may be by trying to get more power the engine is too lean and the prop is too big.

Did you try to richened a little and install a smaller prop ?

rgburrill

I had an MDS 61 that ran fine for 2 years then started getting finicky at high speed. As I recall the consensus at the time was an air leak at the carburetor. Seems the machining on the early 45s and 61s wasn't quite precise enough to get a good seal. Or at least that's what was going around on the newsgroups at the time. Mine was still under warranty so it was replaced with a new MDS 68.

stearman70

Hello. I have it mounted on the stand, I used 10x6 and 11x6 blades, I know how to put the needle valve in the right position, not lean, not too rich, the fuel tank is level in the center of the crankshaft and sometimes little up or down little. The ignition battery is good and I tried to run the engine with and without her.

skorz

Can you check the engine head temp, looks like an engine seizure due to high rpm as you said it iddle perfectly.

I've seen that's on many old used .25 size engine, when the engine stop at full throttle, there is no more compression or the piston scratch a bit.
3min later they run fine again.

stearman70

Thank you. I'll do it.

skorz

And I forgot to say, my mds took a while for the break in, a laser temp gun which cost 15dollars is good, even for gas engine to see if the prop is too big and makes the engine overheating .

stearman70

Thank you again.

the Wasp

My Feedback: (1)

make sure you use the 11x6. raise the tank. as said you need to have the tank centered to the carb. with your tank so low you have to have more pressure.
BTW, do have the tank pressurized from the muffler ??

Jim

stearman70

Hello. Now I'm going to start new tests again.
I'll run engine without muffler ( always it had run with it) , I'll measurement engine's temp ( which is it best temp range ?) , I'll use 10x6, 11x6 and 12x6 propellers. The tank it is at same level with carb. All ducts are fine and clean. I'll report the results. bye.

skorz

Let's say above 115°c there is a problem for a normal plane engine in my opinion, at my airfield with my meccamo fuel.

But to be sure if you have another engine which runs fine, check it first then the mds.

Lou Crane

Just on a chance, I checked "MDS model engine' on Wikipedia. It took me right to MDS website. The Owners' Manual is there. Very probably it could help your problem.
Luck!
\LOU

stearman70

I've finished the job. Same result. The engine works well at medium speed. 8900 rpm and 120°C or 255°F. I used 12x6 (not good), 11x6 and 10X6 propellers. Same situation. When the throttle is coming up, the engine dies. I made a lot of combinations with the low and high valves. .
The tank's level is correct and it has pressure.. I give up for today . Maybe next week I'll try again. Thanks all for your help.

A. J. Clark

How many turns out do you have the hs needle? Just wondering if you can't get the engine to top rpm how you would know your not to lean or to rich??

skorz

120°c is may be the problem, especialy at only 8900rpm, this engine should go around 11000.

3 explainations, or the engine needs more break in, or you are expecting too much power and the engine is giving up by overheating, or simply you get a engine made a monday after a big sales vodka weekend in ussr

the Wasp

My Feedback: (1)

you must use a muffler to pressurize the tank !


culd the O-ring under the carb be missing, or leaking ?


Jim

stearman70

. The O-ring is fine. I always use the muffler, but now I'm going to try it without it, just how it tests. 60 years ago, there were no silencers in Mexico. The engines were sold without them and the engines worked more or less well but with more noise. You used to get used to it.

aspeed

I am responding to mainly subscribe. I have had two motors that I have not solved this problem. Two were solved by polishing the crank where it rubs on the crankcase, not the bearing journals. I have a couple MDS / Uchtkam motors which have too much clearance there and fuel dribbles out.the front bearing, so they had some quality control problems there. You will know this is the problem by touching the bottom of the case to feel if it is hot. It should only be a little warm. You could try taking out or adding a head shim too for more or less compression. I think maybe the newer motors have a bit too large of a carb hole than is needed. Maybe they were a bit optimistic of the power that that they could make. Maybe a sleeve in the throttle barrel to bring this diameter down a bit and check that there is good flow when opening the needle by blowing through the tubing and opening the needle a few turns past where it is running at. The muffler pressure fitting may have a too small hole as well. I had a bad batch of fuel this year that was doing that to a few motors. Some of these Russian and Chinese motors are puzzling at times. More of a kit. I have seen some nasty ones. Uktkam, CS MDS GMS and even T Tiger.. They can work great though when sorted out.

stearman70

Thanks a lot. Very illustrative your information. I think I'll do three things before I put it in the memory drawer. Although the engine isn't new, I don't know your chance. I'll try to break it like it's new. I'll check the inner diameter of the carburetor needle inlet and check the temperature of the carter's base. I'll keep you posted.

jaka

Hi!
Too much nitro will present the sympthoms you tell us! -Impossible to set at full throttle!
Second You have to use a silencer/muffler on the engine! Other vise you cannot pressurize the tank (which you must do).
Third...Use a 11x6 or 12x6 APC prop! 10x6 is a little too small prop for it.
Fourth...Use an Enya 3 or OS 8 glow plug.
Fifth ...The MDS engines are made to run on low nitro fuel. Use 20" Castor oil or 20% all synthetic oil or a mix of the two and max 5% nitro.
No running in is needed in any modern glow engine as all modern engine are either ABN, AAC och ABC made. The only thing you have to do is set the tank properly, center of the tank inline with carb orifice and as close to the engine as possible...and of course set the needle (at full throttle) a little rich and run the engine with rpm altering between a little rich four stroking and clean two stroking...but not slobbering rich!