Bax

My Feedback: (11)

If your Sundowner 50 is a model originally intended for a .50-size two-stroke engine, then the .95 FX would be considered grossly large. That would encourage air being introduced into the fuel by the engine's vibrations. This air will lean the mixture and cause the engine to die.

Put the engine on a very solid test fixture and see how it runs. If it runs "all day", then there are no problems with the engine, iteself, but in the engine/airframe/fuel system combination.

flyboy0608

Hello,....I have the answer to your headaches my friend !! !

I had this issue with this particular engine along with other OS95AX users and it has baffled the best of the best of pros with these OS engines. THE ANSWER IS THE GLOW PLUG. They don't like anything but the F PLUG. I know that some oldtimers refuse to accept that an OS engine does not run well on a #8 plug. But this one does not. After several months of agony and many tests. I changed to an F PLUG and wala !!! Engine runs great. Have been runing on an F plug for about 3 months now straight and absolutely no cut offs, no dead sticks, no nothing. WORKSGREAT!! After you make sure your fuel tubing is not too short as that may also cause you some problems, change your plug to an F and problem solved my friend. Let us know how it goes !!

Alex

barkleyb

My Feedback: (93)

I'm having all the same problems as above with the OS 95 AX - I think it is time for OS to become more involved in solutions for this engine as its marketability is definitely being questioned. Does anyone remember the fiasco of the 91 FX when it first appeared? "O" rings were wrong and the heating of the needle valve really messed up settings.

I buy OS products for the quality that I expect and pay a premium price for that privilege. I also have damaged some nice planes using this engine and I'm not a beginner. You'd think by now that the recommended prop sizes would reflect reality etc!

Bax- thanks for your input but I'm afraid you are in a difficult position here.

ozzy23

I purchased an OS 95 AX about four months ago. I installed it in a Wot4 XL using its own exhaust, own plug and mounting it on its side. It ran fine on the ground, but after 3 to 4 minutes of flight cut out on a regular basis.
After seeing this thread I then used a type F plug which eliminated the problem. I have recently put the engine into a Seagull Zlin 50, again side mounted but this time with a Just Engines Pitts silencer.
Its reverted back to the old problem. I am still using the type F plug, I have even tried the bar type. I have checked the plumbing and asked several different flyers to set up the needles as they would normally do but it still stops at around 3 -4 minutes and with about half throttle.
Any ideas?

Bax

My Feedback: (11)

Your symptom is that of a too-lean engine. Very likely, your exhaust system does not provide enough pressure to the fuel system to give you good fuel flow. As a result, the engine gradually overheats and then quits. You may need to reduce the exhaust outlet area of the muffler to increase the pressure sent to the fuel tank.

ozzy23

Thanks Bax for your reply. I have recently spoken to "Just Engines" company within the UK and they have said the same thing. I am hoping to fly this weekend with one of the two exhaust outlets blocked up to see what that does.
Thanks again for your reply.

saskfrenchy

I have 2OS 95AX that I bought in 2009 and they ran great till summer 2011. The engine would be getting this mid RPM burbling noise and would quit without warning. I could get the engine to run great on the ground and then it would quit in the air. I pushed my troubleshooting and during summer 2012 I got 10 dead sticks. A true intermittant problem that made me sweet. All successfull landing with talent and luck.
I could go on and on to tell you my troubleshooting but lots has been said on this thread. What fixed my OS 95AX problems just before I was about to give up was to add a gasket under the head from my second OS 95 AX. YES! add a shim or gasket, what ever you want to call it and watch that engine come back to life. It is possible that just replacingthe head gasket with a new would be OK,but this is working great for the past 6 flights.

Bax

My Feedback: (11)

Adding a head gasket will work if the engine's overcompressed for the fuel being used. More nitro means you should lower compression. Less nitro means you should raise compression. Lowering compression can help a lot in some cases.

richrfl

My Feedback: (2)

I am having the same problem that all around in this thread. My engine is mounted upside down, I guess that because of the size of the propeller I cannot reach the high pitch sound at high speed as with the .61 or .45, but it has being hard to adjust the low end. I am using 5% nitro gas, and OS A3 plug and an exhaust deflector. Any suggestion to this setting?

Given what I read in the thread, it looks that it would be a good idea to adjust the engine upside first. What I have seen in another model, is that when you turn the model upside-down to have the engine upside, the muffler line is located in the lower part of the tank, and therefore the muffler is flooded. The question is, I can strangle the muffler line to start the engine, but what I have to do after starting? If I keep the line closed there will be no entrance of air and the fuel will not flow for too long. If I release the line will the fuel flow towards the muffler??

Bax

My Feedback: (11)

Turning the airplane upside-down to start the engine won't affect the muffler. Fuel should not siphon out.

You want the engine to be turning up to full RPM to get the needles properly adjusted. Since you didn't say what propeller you are using, we can't tell you if it's too large or what. We'd strongly suggest that you prop the engine to turn around 11,000 RPM when at full throttle. Propping it to turn near 12,000 would be very good, but also much louder. We like a 13 x 8 propeller or a 14 x 6 or 7. They'll let the engine turn up, but it won't be a quiet as with the props O.S. likes to use.

richrfl

My Feedback: (2)

Sorry for my miss. I am using an APC 13 x 8. Will try this after my return home in a couple of weeks.
Thank you for your advice.

N1EDM

My Feedback: (2)

**

richrfl

My Feedback: (2)

N1EDM, think you for your response.
Interesting. I found out today my friend was running the same engine with a 14 x 8 also, and had not problems. Now, here is my problem: A further review of the installation, showed that the tank position is above (way avobe) of what OS suggests. Way high. Bad news, is that because this is an ARF (phoenix PC-9, .91) I cannot move neither the engine nor the tank.
Therefore, from now on, I follow this new issue in
http://www.rcuniverse.com/forum/show...5&goto=newpost
given that the problem moves from the propeller to the tank location. (And I am going to the 14 x 8 without arguments, to start with)

N1EDM

My Feedback: (2)

Glad that that worked but sorry that I jumped in here... I didn't see that this was the official OS Engines Support Forum. When I realized it, I deleted the msg (above) but at least you got the info.

I love my 95AX. It rings like a bell.

Sorry for jumping in here, Bax. Mea Culpa.

Bob

N1EDM

My Feedback: (2)

Glad that that worked but sorry that I jumped in here... I didn't see that this was the official OS Engines Support Forum, so I shouldn't have posted here. When I realized it, I deleted the msg (above) but at least you got the info.

I love my 95AX. It rings like a bell.

Sorry for jumping in here, Bax. Mea Culpa.

Bob