microsprint9

I'm just breaking in a magnum .15 and something seems weird, the manual says to open the high speed needle 2 turns to start, then lean it out. My problem is that i just barely got it started with 1.5 turns out and find it will only run in a rich 2 stroke with about 5/8 of a turn out, the needle is very sensitive and if a even put my finger on it the RPM will go up 700. I think the problem lies in the pressure line from the muffler, with this disconnected it runs fine at 1.5 turns out but soon as i hook it back up the motor loads up with fuel and will sputter til i turn the needle in. I'm running a dubro 4oz tank and on my break in stand the top of the tank is below the needle. Is there really enough pressure in the muffer tap to push that much fuel into the motor? What is the usual high speed needle setting? I want to get this figured out before i mount it on a plane.

downunder

That sounds to me like you may have 2 problems. One, the needle valve is too loose on the threads so just touching it moves the position of the needle and leans it out. Two, the needle itself may not be closing completely when the barrel bottoms out on the threads so it's always slightly open. I don't know your particular needle valve set up but some types have the needle force fitted through the barrel with a small length showing through the end of the barrel. If it's not closing completely (not long enough) then the needle can be tapped further through the barrel. I had the same problem with an old OS once, even with the barrel fully closed it still ran in a slobbering 4 stroke.

The pressure line won't be the trouble because any engine will run quite nicely on the bench without muffler pressure so long as the needle is opened quite a bit more.

Flyboy Dave

My Feedback: (21)

....and problem #3 is the low speed needle may be set too rich, throwing off
the high speed, and the over-all settings. Try leaning the low speed needle 1/8
of a turn "in" (clockwise) a few times, and see if it improves. Leave the main
needle at 1 and 1/2 turns out....just lean the low speed. It should improve when
you get closer to the correct low end mixture.

FBD.

gcb

In addition to the above, I would suggest bench running it without pressure. Needle settings will probably need to be readjusted after break-in anyway.

I have an older 15-XL so the instructions may have changed. On mine, at step 7a it says to open the throttle half way. It continues with the starting procedure, then at step 8 it says to set the needle at max, 9 says to richen 1/4 turn...BUT nowhere does it say to open the carb to full open until step 11 where it says to run for 15 minutes at various upper ranges of RPM. Then it explains how to set the idle. Does anyone use these instructions as written?

George

WMB

My Feedback: (1)

I ignored the instructions when I broke mine in. Used an APC7x5. The pinch near tdc was squeky tight so I used a heat gun aimed at the cylinder and head. Once I had no pinch I started it and peaked it immediatly, richened just barely to bring off peak. Ran at full throttle for 1minute and let cool. Did that about five times, then used the same procedure except ran for 2 minutes a few times, then three minutes a few times. I considered it air worthy after 20 minutes of run time.
I tried this method after reading about a similar procedure for the LA15. Now I have removed the thick shim, using 30 % and flying with APC 8x4. It has been reliable and easy to start. 10 minutes at full throttle with 3oz.
My high speed needle is super sensitive. I think the taper on the needle is too much and the threads are too course. If I just put a side load on the needle the rpm's change quite a bit.
When tuning for flying, I initially richened from peak by ear. It did not run correctly in the air at this setting. What works for me is to run at peak and barely richen. Then point the nose of the plane up, if it doesn't sag it is ready to fly. Set this way, there is no audible change in rpm from peak to flying setting.
I now have about 60 flights on it and it runs great.
In the spring with the temps in the low 50's, this combo just screamed. Now that it is in the 80's and 90's, the engine is a little more difficult to get tuned to perfection. The plane doesn't fly quite as nice also. I started with a 4oz tank and then used the 3 oz tank. I think the 3oz gave a more consistent engine run from full to empty.
Overall, the engine is easy to use. Have fun with it. MikeB