rcjunky67

Hey Guy's, I'm having tuning trouble with a new magnum xls120ar 2 stroke. I feel like the idle is dialed in good and ai'm about 5-600 rpm rich on the hsn. my question is this , transition is good, and being new, and having ran about 6 tanks of 5%nitro (12oz test stand tank) 20% castor oil coolpower with the recommended 15x8 prop and the recommended long glow plug. she does pass the pinch test for both needles. problem is, if I let it run at the midrange for about 30 seconds or so, like level cruising speed,then open it up,she just stumble a bit and dies.Every time. is this more of a new engine thing or is it something inherent to carb.any advice would be most appreciated.

jeffie8696

What "long" glow plug is it?

rcjunky67

can't remember the name off the top of my head jeff, and I couldn't believe that my lhs had one and they couldn't believe that I was looking for that specific plug,but it was the one recommended in the manual. I also tried an OS F plug, and anOS A3, and a A8,and an A5. all new and all had the same result.I think I did see some difference in top end rpm, but no difference in idle quality or transition.
I've tried to do my homework and I've read that these carbs can be tricky to adjust, and the last time I ran this engine , the lsn adjustments I was making were as slight as possible,1/32 turn at a time. trying to clean up the midrange. I'm not trying to get a real low Idle rpm, around 2,800+- just a little less than what would actually make the seagull ultimate 90-120 move on the grass.also it doesn't seem to matter cold or hot.
just like our on road vehicles, we don't and can't drive everywhere at full throttle, and while that may be OK for a lot of smaller glow engines,it's not the way I fly bigger ones. it seems I can remember reading somewhere that removing 1 head shim/gasket and a certain plug with low nitro content fuel can make these engines 'down right friendly' , but I don't recall what thread I'd read that on. thanks for any help you can give

1QwkSport2.5r

Use a hotter plug yet. McCoy MC55 or MC59, or the really hot MC14. I don't think that'll cure the trouble but may lessen it. Likely the needle taper needs to be adjusted some?

jeffie8696

If the needles are adjusted rich on the high and low speed your midrange with also be too rich . Midrange can be the hardest to adjust because you don't have a needle to play with .
I would say start over with your high speed adjustment and try to lean it to peak then richen to a 200 rpm drop then go back to your idle mixture and try to get a good low rpm with a nice lean idle without being too lean. You say it passes the "pinch test" I have seen some "experienced" modelers pinch test the low end but they only pinch for a split second, it takes sometimes several seconds for the engine to burn off the excess fuel in the system so pinch and hold at idle , you should get a slight rise in rpms then it should die. I would go ahead and try for a good 2300 rpm idle, that should get the idle needle well into the seat and control the mixture better.

rcjunky67

thanks jeff, and I always count 3 indianas on my pinch test . and right about the time I get out the last 'a' sound, she picks up just a little then dies. I guess I should add that as long as I don't linger in the mid range , she passes through it pretty well. thats why I'd asked if it was a brake in thing. as I've come to understand that ringed engines can take a little more break in time than I'm used to.
I should also mention that the results i'd gotten where with it mounted on the te bench and the stock muffler. I've since mounted it in the plane it will fly in and it's laid over on it's side with a bisson muffler on it. I'll also be running a perry pump and sullivan glow igniter.
had to take a break for a while. bought a house on 4 acres surrounded by open pasture on all but one side. I had toi gut and rebuild a barn for our quarter horses and tear down and rebuild a boat load of fencing . but now everything is squared away and I finally can resume where I left off. oh yeah, forgot to mention , I was born in lagrange indiana, thats why I count that way.thanksagain

jeffie8696

Personally I just don't think any engine can truly break in on a bench. My mid size engines always seem to transform at a gallon while flying and become a well mannered machine. Might take a little more with a large engine like yours.

Mr Cox

I suspect that the Bisson muffler might have something to do with the problems here. The muffler gives poor pressure to the tank, so at full throttle (where the pressure should be the highest) the main needle will have to come out compared to a regular muffler. This can then give you a too rich midrange.

Try blocking one of the exit holes and retune both needles, and see if that changes the midrange in the right direction too.

rcjunky67

hey jeff, sorry it took so long to come back to this, and I knew I still had the paperwork/manual that came with my 120 ar . in it , it say's, " we recommend using a thunderbolt rc long reach glow plug" . I've not had a chance to mess with it cause I've had a lot to do. hopefully this weekend will afford me the time and hopefully no rain, so I can get it running again and get some fresh #'s together and see where I'm at.

the only thing worse than not being able to get a model you really want is, getting said model, putting the dang thing together with all the goodies,and it end's up staring at you for two and a half years wondering why you haven't flown it yet. got a lot of $$$ tied up in the dang thing at that. oh well , someday soon.