captinjohn

I am helping a friend trying to get his OS 1.20 to run right. We got it to start & Idle real good, but it will not stay running on higher RPM. Could it be the #8 glow plug or bad fuel? We checked the fuel lines ....ect. Any Ideas ? We have tried about everything. Thanks in advance........

1QwkSport2.5r

Change the glow plug, change the fuel lines inside the tank, clean the carburetor out (mainly the high speed needle valve holder), try different fuel.. That about sums up the main stuff. Is the engine being run in an airframe or on a test stand? If in the airframe, try moving it to a test stand with a known good fuel system and try running the engine. If the engine runs good on the bench but not in the plane, obviously the problem lies within the plane.

captinjohn

The engine is on a Spacewalker I believe. What are some of the better glow plugs for this OS 1.2 ? The fuel lines are like new. Fuel (Omega 10 % ) I think could have went bad...so we will try new tomorrow. Thanks, again....

1QwkSport2.5r

If the head is actually cut for a medium length glow plug, I'd use an Enya 3. If it's cut for a long plug, I like McCoy MC59, Merlin hot (red), or even a K&B 1L should work. Ideally the plug should be flush with the inside of the combustion chamber, but a shorter plug won't hurt it other than maybe cost a few rpm. In a pinch, guys use the Fox miracle plug or an OS F too though I avoid 4-stroke plugs in 2-stroke engines. I'm a bit demented though, so YMMV.

captinjohn

Thanks for the glow plug tip. I got a Fox miracle plug....if can find it ! Best Regards John

1QwkSport2.5r

Good luck with the engine.

TFF

The larger OS 2 strokes actually like the 4 stroke plugs. 1.20s and 1.60s; I think the large piston area really likes those plugs. An OS 8 is just as good, but the FS plug seem to mellow the tuning.

dingo9882

How many flights would you say are on the engine or is this new??

captinjohn

The engine has about 30 flights.

dingo9882

I know you may think this is a long shot or not possible...but I have had that same engine for I would say about 9 or 10 years. I was having the same symptoms...I would have some good flights and then it would dead stick, run erratic, and not go up to full throttle. This was all at around the 50 flight mark. What it ended up being was the bearings. I found out I am not the only one with this issue. The bearing just go in this engine. I just replaced my bearing a couple months ago...again for the 4th time....I at least got a couple years out of this set of bearings. Check to see if there is any wobble in the shaft...Just an idea...could be a long shot.

captinjohn

It could be a bearing problem. I have read that tiny metal particles can flake off & ruin a glow plug. It does not always burn the element out, but messes up how they perform. Did engine conversions with another guy online & used his advise. He always used a older plug to do the first engine runs so any metal particles would not ruin a new OS F plug.

blw

My Feedback: (3)

I keep a few break in plugs. You will get more metal thrown around during break in than during normal running wear and tear. Same goes for fuel that I suspect is loosing it's punch, or just getting too old. I set it aside for bench running.

captinjohn

The engine has very good compression & starts with just one or 2 flips. I cannot imagine it is anywhere near worn out. I would work with the guy on it today, but he is going on a trip for a few days. My guess if he tried new fuel & a different glow plug the OS would wake up. Its his call though. Thanks for all the replies....that is a good thing !

Best Regards, John

jetmech43

My Feedback: (9)

The bearings on the 1.60 and the 1.20 are garbage, replace them

BelAirBob

I think I have an A3 plug in mine. I had a similar issue with an OS engine and cant remember if it was this one, but it was running too rich although it did not seem to be. Every time the engine died, it leaned it more and more at every restart until it ran great. Seems sort of strange, but the OS engines of the last few years seem to behave differently than say 10 years ago or older. The newer ones like the AX series seem to start much easier but the needle valve setting seems to be more critical.

It is probably something with the tank or tubing or bearings, but never know.

Let us know what you find.

captinjohn

Yes 10 -15 years ago I thought the OS carb was the better of most. Now I do not know about the bigger carbs on bigger OS Max engines. I did buy some new plugs to try...when my friend gets back...........

airraptor

My Feedback: (66)

I run the OS F plug in all of the OS AX line 65 and above. The 120 I know well and one issue with all of the AZ line of engines is the power to weight. You need to look at the head and if there is any castor burning on the head at all around the head and liner then the head needs to be lapped to the liner. The AX line of engines run great until the over heat/run lean. They do not have that much aluminum built in to keep them light so they are not as for giving to high temps. many times well all is normal and then they start to mess up on the top end its the head gasket is leaking. On all of these engines you need to check the head bolts often. once they start to get lose you need to stay on top of them. Once they get a little castor residue under the liner shim and head they keep getting worse.
They are also very easy to fix this issue once i happens. Lapp the head to the liner with the shim removed. use some fine lapping compound for valves. Lightly lap it until a nice even and clean seal is visible. Dont take a lot of material away as very little is needed.

captinjohn

I think I will help my friend lap the head to the liner....I did find the head bolts loose before. Thanks Mr Air for the tip.

airraptor

My Feedback: (66)

Ok hope it helps. once they get loos they leak and suck air at the same time and run very rough and inconsistent.