Just purchased an FL OS91 4 stroke, the pumped version. In trying to break it in I followed the instructions, opened the needle valve 3 1/2 turns and started the engine but it would hardly run. I ended up with the needle valve only open 1/2 turn from fully closed.

After running a couple of tanks through I did one flight but it seemed to not be able to get RPM up. In attempting to tune up the engine I ended up being able to run the engine with the needle valve FULLY closed. It would idle fine and build up to max RPM. It would run at about 1/4 turn out but wouldn't build to full RPM.

So, I can't figure out what to do. It looks like the pump is putting out too much pressure but there doesn't seem to be anything I can do about it. Also, I seem to be going through plugs. What happens is that I'll start the engine (about 1/2 turn out) and it'll run but if I pull the glow starter off it'll quit running. I put a new plug in and seems fine. When I pull the plug, it lights up just fine. Looks like either the platinum has somehow come off or the pump is quenching the plug.

Any help would be apprciated.

The regulator is probably gummed up and passes full flow?

It is a brand new engine. What do I do to "clear it"? I plan to take the engine out of the plane and clean / blow out everything I can. My thought is that I've got some kind of air leak but I won't know until I get it out and apart. Just doesn't seem right for a new engine.

If its new don't mess with the engine just send it back.

It would simplify your life if you had a regular Surpass II and not the pumped version?

Try running it without the pump hooked up, and see if it will run like
a regular engine. Also, lean out the low speed, and see if it helps.

FBD.

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If you are an experienced modeler that has broken-in engines successfully before, as long as the engine is getting enough fuel or more than enough, I would let it run for a while at part throttle. Make sure that the model is up off the ground and restrained properly. We don't want the engine sucking dirt from the ground into the carburetor and this process may take a while.

What you want to do is to give the fuel flowing through the pump a chance to clean out any possible coating on the diaphragm and let is loosen back up a tad. This affects the pump's calibration. It isn't time to panic just yet.

On the other hand, if you are a newbie, which it sounds like because you are trying to tune the engine for perfect manners with only two tanks of fuel through the engine, you must understand that it takes a while and a bit of running in order for a glow engine, even an OS, to break-in sufficiently to make fine tuning have any meaning at all.

If after several more tanks of fuel at a rich setting, with the model elevated safely from the ground, you are still having problems, it may be time to contact Bax here at RCU, or to box up the engine and send it back.

Whatever you do, do not disassemble the engine yourself in an attempt to repair it. The pumps on these engines are expensive and there are no user servicable parts inside. Let the warranty folks do their thing without you voiding the warranty.

Any chance you or someone else put after run oil in it?

Bill Vail

I recently acquired a NIB OS91FS SII with pump. I opened the needle to 3 turns, fired it up and it ran fine, performed the break exactly as written in the instructions, mounted it inverted on a 60 size UCanDo, peaked the high end for maximum rpm and haven't touched it since. Will start on the low end after a few more flights.
The point is, if it didn't run right after complying with the instructions, send it back and get a new one. They cost too much not to.

Regards,
doubledee

I've broken in a number of engines in the past. The engine would not run at 3 1/2 turns out, even at break in. It wasnted to be about 1/2 turn out. As stated, I can now run it with the needle valve fully closed. I plan to pull it to see if there are any obvious things plugged or leaking hoses. If not then back it goes.

Thanks for your input. If "DoubleDee" had one operating properly then mine should as well.

I have an OS Max 91 fs Surpass also doing the same thing.... yet runs and idles fine IF fully closed top end, It's nopt the surpass II and i cant seem to find tuning info, The os site dosent show it, all others but not the surpass 1.

It used to peak on high end 1/2 tune out the yesyerday it wouldnt and does peak or VERY closed fully closed.

Ive taken the carb off and apart and totally cleaned and blown out, Perfect but still same problem.

Does anyone have factory settings on this carb?

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It sounds like you and the other gentleman's pumps are kaput.

The Perry VP-30 pump utilizes a vent hole in the pump body. If this hole is plugged with debris, the pump loses its ability to regulate properly. The OS pump, since it utilizes a diaphragm too, must certainly have a similar means of venting the backside of the diaphragm. I would look for an opening that is plugged and then unplug. What have you to lose? Good luck.

Mine has NO pump ......

At the risk of repeating myself, if it is new and you can't get it to run right, send it back while it is still under warranty. Don't keep fooling with it and end up banging your head against the wall.
Send it back, send it back, send it back. That is what warranties are for.

Regards,
doubledee

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It has no pump, yet it runs with the needle valve closed? Or am I mixing up two different posts?

Ok, on the advice of doubledee (ggod advice I may add). I took it back and exchanged it for a new )S 91 pumped. On this one, I broke it in with 2 tanks - it seemed to break in the same as the other one. Now, I have NOT changed the low end at all. I now have 10 tanks through and have found the following:

1) It now idles much better (DUH - to be expected with some breakin).

2) If I just go and start it cold then the needle valve needs to be open at about 1/2 turn from fully closed. This will let it idle and accelerate fine.

3) After one flight I change the needle to be about 3/8 of a turn out and it now runs just fine.

4) I have not been burning through "F" plugs with this engine.

So, I expect that after a few more tanks I'll do some low end tuning but it appears that it wants to run between 1/4 and 1/2 turn (3/8 seems ideal right now) out on the main needle.

I can find ZERO information from OS. For breakin (and indeed for starting) they suggest having the needle out 3 to 3 1/2 turns. And while mine would start like this (as long as the glow ignitor stays on), I need to quickly turn it back in to only 1/2 turn out.

My well broken in O.S. 91 Pumped Surpass runs a little rich at 3/4 turn out from closed with a 15-6 APC. My U-Can-Do 60 is just a perfect match for this engine. It seems to have a very narrow adjustment range, with 1/2 being the lean point.

Correct, This os 91 fs surpass has NO pump and high end needle fully closed its still a tiny bit rich..... its not a new motor so i cant return..... if i put the high end needle 1-2 turns out from fully closed i doubt it would even get off the ground.

What are we overlooking, has to be something simple, I wonder if the hole the high end needle stops up gets wore and bigger hole?

The orifice hole in the carb body gets enlarged by one or both of two factors.

One the steel needle vibrates in the hole and enlarges the orifice.

Someone closes the needle down hard against the orifice thereby enlarging the hole.