GRandolph

I am having trouble with an OS 95AX. When running the engine at mid to high throttle, the engine will have brief mis-fires where the ignition seems to stop for a fraction of a second. It's as if it has a loose spark plug wire but obviously this isn't the problem because it's a glow engine. The engine is broke-in and has about 40 flights on it. I have tried two new glo plugs - first swapping the original No. 8 with a new No. 8 and now I have a new A5 but it still Mis-fires. I have changed the fuel lines, the fuel tank, and the fuel but this did not help. I am currently running a 15x6 APC with 10% nitro and 18% oil. I tried 15% nitro but this seemed to make it worse. The transition from low to high throttle is good with no problems. There are no visible bubbles in the fuel line when running. I am thinking there might be trash in the carburetor needle valve. Any ideas what could cause this?

jaka

Hi!
Probably too much nitro! If an engine misfires and is very sensitiv to needle setting and cannot be set to max rpm without stopping its too high nitro content (too much heat which means pre ignition).
Try 5% nitro!

Sport_Pilot

Is it surging?  On and off at regular intervals.  Several reasons for that.  I know the extra thin wall pick up tubing supplied with some tanks will cause this with larger engines.  The line will collapse causing the fuel to be cut off and when the engine slows down will open up allowing fuel to flow.  The rusult is that the engine runs on and off at a regular beat.

GRandolph

Sport Pilot, it doesn't surge or cutout on a regular frequency, just randomly intermittent. I have put in new tubing that feels thick and rigid so I don't think it is collapsing.

Jaka, when I tried using 15% nitro it seemed to make the problem worse. So you might be correct that going to 5% nitro would help. I did notice some pre-ignition on a couple flights when I was breaking in the engine a while back. Strange though how it mis-fires but with no pre-detonation noises. I will try to get my hands on some 5% nitro.

I wonder if an o-ring is intermittently leaking on the high speed or low speed needle?

Long J Silver

I had the same trouble, then replaced the glow plug with a Four stroke plug, now running great on 15%

GRandolph

Long J Silver, I will try an F plug when I get off work. Can't wait to try that! Sure hope it works. Will let you know.

Here's the plane that I have the 95 AX on. I think this picture was taken with a 120 AX though. The 120 was too big so I replaced it with the 95AX this spring.

GRandolph

I tried an F glow plug and it made a big difference! I think the problem has been solved. Thank you for your help.

Desertlakesflying

My Feedback: (28)

Use F plugs in all glow engines and you will have a whole lot less problems. Especially in anything over 60

mike109

G'day

I have a Super Tigre 51 which was behaving badly and I put an OS F in it which made it a much happier engine. Fuel was 10% nitro, 20% oil etc. Then I put an Enya #3 in it. Brilliant. Even better than the OS F.

More recently a friend bought an OS AX 75 and he was having problems with it. I changed him over to the same fuel I run and it was better but not great so then we put an Enya 3# in and it has been there ever since. It really sorted out the engine.

And last weekend a friend bought a new AX 95 in and was also having similar problems to you. He was using an OS 7. He then tried an OS 8 which was better but not great. Then I gave him an Enya #3 and again it sorted the problem.

I am beginning to really like Enya #3 plugs. I am told they work well in four strokes too but I have not tried them there. I still use either Saito or OS F plugs. Enya recently started selling a four stroke plug but there are none around here to buy. I may buy some from Enya direct.

Cheers

Mike in Oz