Hi guys,
I'am having a problem with an MDS 78. It's only had maybe 1/2 gal. of fuel run through it, runs fine at full throttle, runs for a few seconds at 1/2 throttle and then dies. Its sluggish on transion from closed to full throttle. It also seems that the compression is low, doesn't have much resistance when flipping the prop, [ my OS 40 LA has more]. It doesn't really draw fuel when you open the throttle and choke it. I'am using the H9 super plug that came with this engine, using Sig 15% Champion fuel, any suggestions?

I see your from Minnesota, I'm from Richfield. I got one of those MDS 78's too. 60 Bucks is a good price. Here's the poop, No nitro, yup, no nitro. This engine wants plain old FAI fuel, period. I got some morgan 0% and added a little extra caster for break in. Put it on a stand and run 3/4 gallon though it. It has a steel cylinder with a iron ring. It will take time to get the ring to seat. The steel cylinder really holds the heat , so no nitro. I used a wood 12x8 and turn the needle out 5 turns to break in. At 5 turns it blubbers and goes through 8 oz. of fuel in no time. Then do that thing where you pinch the line and lean it out for a bit and then let go and return to a RICH condition. I could hold my hand on the engine during this process, yes that rich. After that the engine had a good pop to it.

After that I put mine on WM p-51 with a 12-8 APC and a nice spinner, the model goes 12 feet than it goes up, up , up. Gotta leave it a bit rich for a while. My low end mixture was too far out. I ended up screwing it in all the way till the barrel wanted to jam at a closed condition and then backing off a bit. I also took the baffle out of the muffler, big help in transition and top end.

Remember, No nitro... have fun.

I also ground .040" off the opening side of the crank to increase port timing and "raised" the exhaust port .005 to do the same. The engine gained a good 600-800 rpm. Since the engine so cheap and the cylinder is steel it's easy to do.

Yeah, I run mine on 5% and it does ok. It doesn't like much more nitro though. Keep it rich until it gets good and broken in. It took mine a long time but it runs real strong now.

Splatt, I see you're from Richfield, no doubt you bought your engine from Hobby Warehouse too. They seem to have the best prices in town.

We're spoiled having HW around. I'll be flying at Grassfield this Saturday if you want to see my MDS fly. Were having a Quickie race and afterward I'll fly my P-51. Like around 2-3:00 o'clock.

Splatt, I may show up at that field on saturday, how will I know who you are? I would be interested in seeing your P51 fly.

He'll be the one with the P-51.

My P-51 is done in the Miss America red,white, and blue colors that I got from HW. Our Quickie race starts at 10:00 and we go about 4 hours before opening the field again for open flying. I have a blue jeep. Ask for Jesse

Go to Grassfieldrc.org for a map. It's right after 610 if your north bound on 169 on the left by the big white pole barn.

Thanks everyone for your replies, running the engine full rich seemed to do the trick. This thing really runs good now, seems to have good compression. Spins an APC 12x6 prop at 12.300 rpm, reliable idle at 2,100. I also had the low speed mixture set too lean. It runs so good that I'm thinking of buying another one!