ORIGINAL: dbmartin
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.
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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.