Magnum XL 70 RFS 4-Stroke Engine (Red Bull 540 Update)

I blasted out an update on the Red Bull 540 build rather quickly. I am stuck trying to get the plane in a fly-able condition. This is why I haven’t had another update on the plane. I can’t fly it!

I ordered a Magnum XL 70 RFS 4-stroke glow engine from If you read the update post you’ll know that ordering from was a pleasure. However, getting the engine to work has not.

I am having some trouble getting this engine running correctly. After searching around with Google and looking through posts here and other forums I cannot find a solution or questions to the same effect. The title of the thread is the main issue. However, here is a bit of background info:

The first thing I did after ordering the engine was bolting it down to my test stand. I then ran about 3 tanks of fuel through it. At the specified two and one half turns out on the high-speed it seemed like it was running too rich, but being in the brake-in phase I wanted to make sure the engine was getting good lubrication.

Everything seemed great while on the test stand. It had power, but since it was running rich I figured that when I had it all ready to go a good tune on the high-speed would give it that last bit of power. Anyhow, after putting the engine on the plane I started running into a number of issues. It seemed fuel just wanted to pour through the carb. The tank and carb don’t exactly line up on a center line. The actual carb may end up being near the bottom 1/3 of the tank. After working with the plumbing it seems to have quit this. However, and this seems to be the issue that is preventing me from flying is that the engine just becomes inundated with fuel.

Starting the engine when cold isn’t too difficult. After letting it run for a few seconds I’ll open up the throttle and go to adjust the high-speed. Turning the high-speed needle does absolutely nothing. Adjusting it further and further in (clockwise) does nothing till I’m about 3/4 to 1/2 turn from closing the needle completely. Depending on how “lean” I’ve gone it will backfire and undo the prop nut. At this point the engine is full of fuel. Also, on the ground is a puddle of oil/fuel. It runs so rich that the whole front yard is full of smoke.

After one run I took the engine completely off the plane to start to look at it. When taking off the valve cover there must have been an ounce or more of fuel in there. It was basically full. Turning the crank back and forth shot fuel out of the exhaust and undoing the crankcase vent shot out fuel (or partially burnt fuel) all over the place.

Things I’ve noticed after the initial break-in:

  • Unburnt fuel and oil just puddle where the exhaust hits. My 2-stroke Super Tigre produces doesn’t produce anywhere near this amount.
  • High speed does nothing in terms of leaning the mixture.
  • Doesn’t sip fuel, it guzzles it.
  • Backfires (?) and breaks prop nut loose.
  • The top of the valve cover was completely black as if there was some major blow back.
  • Lots of oil
    • Comes out of where the high-speed needle goes into the sleeve
    • Coming out of the area around where the back plate meets the crank (this actually looks more like unburnt fuel)

Things I’ve tried:

  • Adjusting the valves (the valve lash was horrible; was almost 2 times the recommended amount)
  • Pulled and disassembled the carb: Got some trash out of the carb and noticed that the o-ring on the high-speed was cut up a bit

After going over the engine and “fixing” anything I could notice with the carb I put it all back together and got the same result.

At this point I’m ready to send it back and say its defective. I just want to cover everything before I do this (expecting shipping to be ridiculous or about 1/3 of the original cost of the engine). No one I’ve talked to in my club has had this problem. They all swear by Magnum engines and for the most part have them on almost every plane they fly.

What gives?!

I started a thread over on to see if anyone there has ideas.

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I'm a software engineer. Look into the about page for more information about me.

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