ifly2

New OS-120AX.. Starts and runs GREAT. Ran about a tank thru it, as per the break-in in manual. However, after a few minutes (2-3) of running, at mid to high throttle, it just quits. I can put the glow started to it, and it will start with 1 flip again, and run for a little longer. Transition seems very good, and since it does it at full throttle, I do not suspect th elow end. ( I have not moved it yet). Put new #8 plug in, no help.. I am usually quite good with glow motors, but this one has me scratching my head..

NM2K

My Feedback: (14)

You are either running too lean, or you have a fuel tank/plumbing problem.

Engines do not "just quit" for no reason. Find the reason and you'll find the cure.

Such things as kinks in the fuel tank vent line will express in the manner that you have described. Good luck.


Ed Cregger

Sport_Pilot

Although the transition is good, if it quits like that after getting hot, then the low speed may be just a touch lean. Since the engine is new both the low and high end should be set richer than it will be after break in.

w8ye

My Feedback: (16)

After being around a 120AX every time I go out to the flying field for the last two years, they do seem to be sensitive to fuel mixture and internal combustion temperature.

Make sure that you have the mixture correct as noted above.

Also you may try a four stroke plug like a OS "F".

In spite of it being a OS engine, they do run a lot better after a couple gallons of fuel.

The engine has the "Powerbox" muffler which has a tuned internal volume. Thus at higher speeds there is a reduced internal pressure and therefore less tank pressure.

When first started, they need to warm up a little at a higher idle speed before the glow plug heat is removed.

ifly2

I am using medium fuel lines. I thought that since it also dies about 1/2 throttle, that should eliminate that. I will pull the tank, and check it all for leaks Thursday, when I am off.. It is not popping plugs, I did change it, just to see if it helped. It did not..

This is a new plane, Has not gotten off the run stand. It is a new engine with about 2 tanks of fuel run thru it. The first per the break-in instructions in the book, the second trying to figure out why it dies.. I checked all bolts, and made sure the backplate is tight, and the head is also.

Fuel is not new, but only about 2 months since I opened it. It runs fine in my OS-160FX (however it has a pump). I also am using medium line on the 160, but again it has a pump..

The filter is used, so I will remove it Thursday, and see if that makes a difference.

If it is a temp issue, would it start right up after it dies, and run fine for another minute or so.. I can put the glow driver on, and bump it with my chicken stick, and it will start right back up, and run for a minute or so again..

So Thurs, I will rip the tank out, and double check it. I usually pressure test all tanks, but did not this one. It is the one that came with the plane. (Seagull Laser 200).


Tank pressure tests good.. Filter has been removed.. I'll run it in the am..

Ok.. Here is what I have today.. Removed the Filter, richened the low end to 1 1/2 turns out. Filled tank to about 3/4. Started engine, it idled for about 3-4 minutes fine. Ran it to full throttle, and checked to make sure it was very rich 4 cycle running, not even to 2 cycle yet. Ran for about 4 minutes (glow stick is still on engine) Ran GREAT. Removed Glow stick, and engine died in about 30 sec. Put glow stick back on, leaned high end to just 2 cycle, went 2 cycle, 4 cycle, 2 cycle for a while, brought back to 4 cycle (just into 4 cyce this time). Ran great with glow stck on, took off, it dies. Put on, and ran rest of tank at 3/4 - full throttle.. I guess I'll try the F plug and see if that helps. It appears the plug is cooling. Too rich?? Compression (feels fine)??

Note.. I had always removed the glow stick before..

ifly2

Update: I think I am getting there... Put a Type F plug in, and ran it.. It died.. Leaned it to a just solid 2 cycle, and ran a full tank thru it at 3/4 - full throttle, varying it it every minute or so.. Maybe I was just was to rich, and cooling the plug.. I will run it again, then if it is OK, put the cowl on, and fly it..

Thanks to all that replied..

sevans16

I have had the same problem with my new 120ax. It starts great. trans good up to full throttle and when you pull it back to 1/2-3/4 throttle it just dies. I redid my fuel lines. Replaced several OS #8 plugs. Took it out to the field for the third time. I have had two very experienced guys helping, me scratching there heads on this one. I tried everything I could think of. I put more foam around the tank. I tried different props. Checked balance on spinner. It would not die when the glow driver was left on. I think?? maybe an "F" plug might be the ticket till it is broke in?

So after about a 1.5 gallons it just start running good. Nothing major changed. Six tanks and she seems OK right now. I did not get to fly the plane due to a broken landing gear from a dead stick landing. It seems the engine just gets very hot and quits. So at this point just make sure you keep her a rich and get a couple of gallons through it before you trust it!! The last tank I ran through it: engine ran great. Like an OS should.

Last setting as of 1.5 gallons: 15% CoolPower, Main 1 3/8 turns out, Low end 1 1/8 out, detuned a 16x6 apc @ 9300 RPM. We got a max rpm of 10K, we set it up to run about 9600 rpm but the engine gets hot and quits. I hope it gets better and real fast. I have never fought an engine so much!!! I am no expert but these are my findings.

rainedave

My Feedback: (1)

I know this gets said a lot. And, some people are probably tired of reading it. Add some castor oil to your Coolpower, about 4ozs. to a new gallon. It will help the overheating problem and the engine will run better and last longer.

David

Zippi

My Feedback: (10)

ifly2,

I am currently running two of the OS 120AX engines with an APC 17X6 prop. It's kind of characteristic of these big two strokes to die a lot when being new. I have never had one of these engines die on the ground, always in the air. I have an AW YAK 54 .90-1.20 with the OS 120AX and it runs fine now. I just maiden my WH Extra 260 with the same engine and once again the dreaded dead stick for a while. I had a Seagull Laser 200 with the same engine and same problem. I can get about three or four laps around the field before it dies. I use the #8 plug that came with the engine and when they start dieing just start changing plugs until you get a little time on the engine. Doesn’t seem to matter if you run it lean or rich they are going to die for a while. I wouldn't waste my money on the "F" plug until you get a little time on the engine.

sevans16

Glad to hear. That is what we determined at my field. Rich or lean did not make a lot of difference. But rich seemed to keep it running a little longer. Just tune it before it get too hot. When it dies let it cool for a bit. I know it will start right up but...; When I first flew it I got in about one circuit. The last flight today I got about 3 circuits. So another couple of tanks and it should be set!! I ran a whole tank through it on the ground today with no problem.

AndresAM

This is crazy, I have the exact same problem with a .55AX: I take off, two circles to the field and it quits. I have tried everything but no fix for it yet. I have read also some posts of people with similar problems in the AX line of engines.

I will be paying attention to this thread, and if I find a solution I will post it here too.

I have like 30 flights and 30 deadsticks, this engine is driving me crazy and I don`t buy the "it will be better after is broken in" theory.

Andres

Zippi

My Feedback: (10)

In my experience with these big two strokes it doesn't take long and it's running great and the dead sticks are history. These engine produce a ton of power and will give unlimited vertical on a 9 to 10 lb plane so don't give up to quick like a fellow did at my field. It will come around very quick.

AndresAM,

If you have had "30 flights and 30 deadsticks", you may be facing another issue. I'm sure at this point you have ran a lot fuel through the engine. I'd be checking for an air leak in the tank system or an air leak on the engine itself. Make sure your not running the engine a little to lean.

jnhiller

The 120 AX is a pretty darn nice motor. I have run one for two years in a 9-pound pattern airplane and never experienced a dead stick. The muffler pressure may be a little weak and the early production motor had a slightly different carb. The mixture needle didn't fully exit the fuel delivery tube, which may have restricted full throttle fuel flow. I added a short length of hose with a brass tube insert to restrict the exhaust to increase tank pressure.

Also fuel isn't what it was 15 years ago. Newer / better isn't necessarily better and when in dought add more oil as previously suggested or try a different brand of fuel. I am currently running Byron 15% nitro - 20% synthetic / castor blend. I have used 18% oil but the motor is happier with 20% oil.

I tried a #8 glow plug and had difficulty adjusting it on the ground (surging and dying) and never put it in the air. It has run flawlessly since with an 'OS-F' plug turning a 16-10 prop. If the engine starts to exhibit problems in the air check the glow plug if the element looks frosty rather than shinny change it. I run a conservative high-speed needle valve setting, barely darkening the exhaust oil. I felt that I burned a case of fuel before it was thoroughly run-in.

When my motor is happy I'm happy.
Jim H.

j.duncker

My Feedback: (2)

Lovely engine.

Mine is sensitive to the plug used. My usual fav, the Enya 3 does not suit my 120 AX giving a fluffy transition from fast idle to half throttle. It likes the OS 8.

It is not particular about the needle settings, I run it several clicks rich and have not touched the needle for months.

I would suspect your plumbing.