I just do not understand why people are having such a hard time with MDS engines. They are incredibly powerful for their size. I bought one 40 size for starters and yes I was skeptical based upon what I read here in the threads… (Now I also have a 78 that I put in a P51) But let me tell you people REED THE MANUAL on how to se these engines to run. Most people want to open the box, mount the engine on the plane, fuel it up and fly. Well if that is what you want then get an OS or a Super Tigre. But still then for ultimate performance you need to tweak the low idle screw to get it to work right in transition. I have had Thunder Tigre, Super Tigre , OS FX, and FP and LA, YS and now MDS. It is strange but I do one thing that most people do not do and that is READ THE MANUAL on how to set the engine to run. For the MDS if you do not have the manual go to the horizon website and downloaded in pdf file or call them and they will send you one.
The problem with MDS is that the engine needs to be se completely different than the OS or other engines out there. Most people say “ I know how to set the engine..” and do what they think is right. Initially I did the same thing, but soon I realized that it does not work for the MDS. Then, the unthinkable! I read the manual on how to set the engine…..
I have to admit that the manual is poor written. Nonetheless is very helpful.

Well, for those of you that you have not red the manual this is how you set the MDS to run like no other of your other engines….
1. Do not use more than 10% nitro (it is still of combustion timing but it will do)
2. Use preferably 5% nitro
3. Use a hot plug like OS A5, A3 (I use A5). I have not used idle bar yet as I did not see a need for it. But others claim to use a spark lug with an idle bar. Either way, make sure your plug is hot.
4. Screw in the high speed needle valve until closed. Open the HIGH needle 2 &1/2 turns (counter clockwise).
5. CLOSE your throttle arm and screw in the LOW idle until it stops turning. Then open (counter clockwise) 2&1/2 turns.
6. Prime the engine by squirting very little fuel into carburetor.
7. Open throttle ¼ turn and start engine.
8. Let engine warm up for 1 MINUTE and then start to increase throttle. This engine needs to be warmed up due to the metals expanding.
9. Start to increase throttle. It will have a rich setting at this point. Start to close the HIGH speed needle TWO ticks at a time until full throttle is reached.
10. Do the pinching test. Pinch the fuel line momentarily at high throttle and listen for rpm drop or increase. If the RPM increases you are too rich, so close your HIGH speed needle (clockwise). If the engine does not change much in rpm or dies you are where you want to be. At this point turn the high needle open (counterclockwise) ONE to TWO clicks as it needs to run a tad rich.
11. Reduce your throttle to idle and wait for 10 sec. At this point the LOW idle will be running rich. With a screw driver close (clockwise) the LOW idle screw 1/8 of a turn. Now do the low idle pinching test.
12. Pinch the fuel line while the engine is running at low idle. If the engine, while at idle, increases its rpm more than 200 the low idle valve is too rich. Stop the engine and close the low idle speed by 1/16 (clockwise). As you keep on doing this you will notice and improvement on transition between high throttle and low throttle.
13. You will have set the LOW speed needle valve properly once you do the low idle pinch test and only get about 100 rpm increase. Your transition will be instantaneous at this point.
14. Last test is the VERTICAL TEST.
15. Start your engine and while in the horizontal position give it full throttle. Now tilt the engine up until it reaches 75 degree pointing up.
16. If you engine is set properly you should have no variation in rpm. If the engine reduces in rpm or increases in rpm increase or decrease the HIGH speed needle by ONE or TWO click.
17. Once you engine stays working while in the up orientation YOUR ENGINE IS SET.
Do this and you will not have any dead sticks and you will fall in love with your MDS.

MAKE sure to break in your engine on the stand for at least one gallon of fuel.
This engines uses automotive metals so the break in time is significantly larger than any other engine. Once you break it n you will have an engine that will last you for many years to come.
Happy flying.
Sincerely Eric