naval flight officer

I am looking for help with my OS 70 Surpass II. It Idles like a champ and will go to full throttle with no problem on the ground. The problem arises in flight when I go to full throttle for any length of time it starts to bog or sputter and genuinly sound like it is going to die. If I throttle back to 3/4 or less it runs just fine. It is in a cub at the moment and I don't use full throttle very often with that plane except during touch and goes and take off climb. Could it be over heating? I am using 10% nitro with 18% lubrication. Any help would be appreciated.
Scott


Moderator changed 71 to 70 in two places.

carrellh

Sounds like overheating. What prop are you running? Have you tried flying it without the cowl?

RaceCity

I think it's overpropped. 13-6 (or equiv) is about right for this engine. 10-15% nitro is all this engine needs, and the 18% oil seems to be about right. I've been using the OS70's since they first appeared on the market, and have seen this sort of behaviour when the motor has a little more prop than it can deal with.

naval flight officer

It is turning a 12X8 at the moment. I will try and fly it with out the cowl and see if that helps.

submikester

My Feedback: (6)

Well, I've been flying mine since the beginning of the year in a Venus 40 with a 14x6 master airscrew prop and 15% powermaster. It runs like a champ and pulls the Venus straight up for ever - seriously. I'm quite surprised at the performance as it is on par with my 91s with the same prop.

Regarding your problems - check the valves to ensure they are not out of whack - also ensure that there is no foaming of your fuel happening. If that happens it could cause a lean condition also causing you to over heat. Lastly - I doubt it is the problem since you say it runs fine on the ground but for good measure check the timing.

NM2K

My Feedback: (14)

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Have you tried richening the high speed needle to see if that helps? Yeah, stupid question - but I have to ask. <G>

Assuming that you have tried the above with no relief, the first thing that I would check for is a kink in either the fuel or the fuel tank vent line. Air has to get in to let the fuel get out. A kink in either will limit the amount of fuel available for running.

Next, check the spraybar in the carburetor for blockages. I had a piece (long thread) of nylon from a Hayes fuel tank get into the carb of my engine at a pattern contest. I couldn't raise the throttle above half throttle without the engine threatening to quit and I couldn't find the problem during the contest. Obviously, I did find the problem when I got home, but it nearly cost me a contest.

Have you changed the glow plug? Yep, sometimes a less than perfect glow plug can manifest itself in such a fashion. Not often, but sometimes. Good luck finding the solution.


Ed Cregger

naval flight officer

I will check on the kink and the debri in the intake. I changed glow plugs on Sat. to see if that would help to no effect.

naval flight officer

I have it running much better now. I removed all of the exess fuel tubeing so that the lines are as short as possible and it runs much much smoother now. Still bogs a bit during throttle increases but runs at a constant rpm at high speeds. Thank you all for your imput.

jimcork1

My Feedback: (4)

This sounds like you HS needle is too lean. Set the rpm with a tac 200 to 300 rpm lower than peak rpm. Check your idle. If it bogs on throttle up your low speed in probably to rich. Do the pinch test on the fuel line while idling to see if it speeds up or dies. My guess is yours will speed up. This is a good indicator of too rich on low speed. Turn in the low speed needle 1/16 of a turn or about the width of the slot in the needle for each move. Lean it then check idle. It should idle faster,, then use throttle arm to slow the idle back down. Repeat the pinch test. When you have the idle about right and you did set the top end 200 to 300 rpm below peak check throttle up. If it hesitates open the lowspeed 1/16 of a turn and repeat until you get a good throttle up. Your prop is close to the right size. You didn't mention what RPM your peak was. If you are in the 9400 to 9800 you probably have the right size prob (after the 200 to 300 rpm drop).

NFO? Jim AFFO [8D]

errie

Definately fuel or fuel system related!!!