Hey, i have an os 46 LA on my supersports 40s and have been having inflight problems. The engine starts fine, idles fines, taxxi's fine, but after about 5 min in the air it starts to run poorly and then just dies. This has has happened to me my last three flights. Unfortunately, this plane doesnt like to glide as well as a trainer so i broke something each time this happened. This engine is only 2 months old and always ran well. Anyone have any ideas about what is causing this? thanks

You say the plane isn't a trainer. Is the engine cowled? It could be overheating in the air.

My first guess, though, is that you're running a bit lead. Try backing out the needle a bit more than you think you should.

Your symptoms are consistant with being lean and/or overheating.

If you fill the tank half way, does the problem happen on the ground? It's possible you have a hole or some other problem with the clunk line inside the tank which only shows up once the fuel level gets below half.

It could be fuel foaming as well, though I think this is less likely.

Old fuel, old plug? Too lean? Air leak somewhere?

Something else a lot of folks overlook- when you fly your plane, do you run the tank all the way out? If you run the tank half dry, then refill over and over, the fuel gets a lot of crud from exaust residue. It's good to empty the tank as much as possible before re-fueling.

Jetts

thanks for the help. yes, the engine is cowled and does seem to run a bit hot, but not sure cause i dont have a temp gun. i have a tendancy to run my engine as lean as i can. i will try to richen a little and see what happens

There's your problem. Too lean, and maybe too hot. Why do you run your engine so lean? It's not good for the engine, that's for sure. Back off a bit, you won't notice much differnece in the air, but your engine will last longer, and run more consistantly.

Wringing every last ounce of power from an engine rarely makes sense. It will result in overly lean runs, as you've already experienced, and one run that's a bit too lean will ruin an engine.

I have engines that are going on 9 years (new when I started flying), and they run like brand new. I always back them off about 500 rpm from peak.
Dennis-

Here's a dumb newbie engine problem for you all: I noticed at the field, as I starting the engine for the 4th flight of the day that the carb seemed to be sort of jumping up and down. Well I did the reasonable thing and shut the engine down (as opposed to just going ahead and flying with a what-the-heck attitude). Anyway, both of the carb retaining bolts were missing. They had apparently vibrated loose in flight. I suppose the only thing holding the carb on was the throttle linkage!

Anyway, back at the LHS (which didn't happen to have replacement bolts) the guys informed me that I really should have used blue lock-tite on these bolts. Live and learn.

Yep...sounds lean to me. I had a 46 LA and it would do the same thing. That little engine ran just fine though at a richer setting. Richen it up a bit and see if that doesn't help. Also this sounds like good advice. I never really thought about it, but it makes sense.

yea that was the problem....i richened it and flew without any problems. it actually didnt lose any power either which is good. what prop would be the best match for this engine ? i am using a 10x6 wood prop right now and it seems to be working ok.

Thats what i was runing on that engine. Try APC props, they are very durable.

That may be a little small, check this out.

One of the guys I fly with uses a 11X6 on his 46LA. It's been a good one for him.

About that "running rich".... actually, in the air, the prop unloads a little, allowing a bit more RPM. At which point, if you peaked it on the ground, you're lean in the air. Glad it's working for you.

Good luck,
Dave Olson

The standard for a 40 engine is 10-6. Go to a 11-6 for a 46 size. Get a MAS for training. They are very forgiving props and will tolerate bumping into the grass field without breaking better than othe props.