brett65

My Feedback: (18)

I had my engine running strong last night, but now it seems like it has to warm up? If I try to go full throttle after about the first minute of idling it wants to just die. Even slowly going to full throttle it does it. After I let it just run for a few minutes, it has no problem. I just broke it in Saturday night and it was fine. I did the whole "super rich" to "little rich" thing and all seemed fine. Any thoughts? Glow plug maybe?

stang

My Feedback: (1)

Maybe the glow plug but first I'd try going more rich. It sounds too lean from your description. Let us know what happens.

ChuckW

Does it just immediately die or does it kind of gurgle and spit before quitting? If it gurgles and what not, it could be rich on the low speed needle.

Also be careful that you don;t get the high speed too lean. I've noticed that is easy to do on the .55-AX. Set it on the rich side then lean it 1-2 clicks at a time and watch your tach. As soon as the RPM's stop increasing as you turn the needle, immediately back it off 3-4 clicks or until the RPM drops 200-400 RPM or so.

brett65

My Feedback: (18)

It immediately dies, I guess I had it too lean. I'll mess with it more tomorrow starting very rich. I think its time to invest in a tach.[>:]

da Rock

Whenever an engine stumbles going from idle up, it could have too rich an idle needle. Could have........ Maybe.........

You really do need to make sure of a couple of things. It needs to be warmed up, and it needs to be cleared out. When you first start one, raw fuel often winds up in nooks and crannies inside that engine. It takes a few seconds at wide open throttle to clear that engine out. Needless to say, you don't go WOT until the engine has warmed up.

Now.
It is a new engine, and "I did the whole "super rich" to "little rich" thing and all seemed fine." may not actually have broken the engine in. The "little rich" part just might not have been lean enough. The idea actually is to get the parts hot so they'll work against each other, not just get them going some bit faster. Until you're sure the engine is broken in, it usually isn't.

First thing I'd do is dead simple. Give the engine one more tank of fuel and that OS break in "dance". Only this time the "little rich" running should be what you consider to be the max rpm the engine will do without sagging off lean. You actually want the engine running at it's highest rpm in comfort. That is what breaks the sucker in. You can do it or not, depending on your confidence in reading it's break in condition, but just doing half a tank will prove the break in or not.

da Rock

When a broken in engine stumbles when coming up from idle, the pinch test is called for.

(A broken in engine will hold a very low idle for as long as you've got patience to watch. A low idle is one that allows you to land the airplane comfortably. It's more than slow enough that the airplane just might stall on approach if you pull the nose up too much, but absolutely won't die on you.)

Get the engine warmed up and cleared out. Then let it idle for awhile. Now pinch off the fuel line. If the rpm increases just before the engine dies from starvation, the idle setting was too rich. Give it about 1/8 turn and check for stumble again. If it still does, do the pinch test again.

CGRetired

My Feedback: (1)

Brett: I follow this simple break-in for my OS's. Pretty much what DaRock said, but just to clarify what should happen I offer this:

Start the engine ( ) then allow it to warm up for about a minute. Then slowly work it up to full throttle and do what's necesary to get it there. As soon as it does, rich it out to the point of sputtering fuel/oil out the exhaust and leave it there doing it's 'four stroke' thing. After a minute, lean it out to full lean and maximum RPM and let it set there for about 20 seconds, then quickly richen it to the point of sputtering again.

Continue this for the full tank, shut down and let it cool for about 10 minutes, then do it all over again.

Once through the second tank, it should be reliable enough for flight but flying with it on the rich side of lean. As you fly it, on subsequent flights, as you go through a few tanks, it will run better and can be run up to a tad more lean. But, I always fly mine with a visible smoke trail in the sky. Many (if not most) will tell you that does not mean anything, but at least you will know that it is running slightly rich. Another sign will be all that crap you have to clean off of the wing and tail feathers afterwards..

Watch for black sooty looking residue, though. That usually indicates wear and that you may actually be way to lean. I use a colored fuel, and that color is clearly visible on my wing and vert/hor stab without any black anything coming out of the engine.

There may be, and probably will be, lots of suggestions, but the above works fine for me and my OS engines.

I do know, however, that my OS .75 AX was not running well one day, would dead stick on me or quit on the flight line before take-off, so I simply changed out the glow plug and that was that. They do wear out.

CGr.

da Rock

Yeah, it could have too lean an idle setting. But of the couple of dozen OS46AXs and the OS55AXs I've seen in the last few years, every one that didn't have a good idle needle setting had a very slightly rich setting. The ones I saw that hadn't had some fiddling already done and were rich took only one or two 1/8 tweaks. It's so predictable, that I'd bet big money that OS has perfected an very accurate air guage or somesuch for setting low end needles at the factory.

But on the chance the low end is the problem, and that it's a problem from beeing too lean, the pinch test is still the best.

When you pinch off the fuel completely, the idling engine will simple stop when it runs out of fuel. It's already hurting for air, and been hanging on to what little fuel is coming in, and simply stops when that little bit of fuel stops coming.

RCKen

My Feedback: (9)

Brett,
To add to Da Rock and CGretired have said. The break-in for OS engines is much much more than just one or two tanks of fuel like the manual says. It can take upwards of 15-20, or more, tanks of fuel through an OS engine before it settles in and starts running well. This is completely normal for an OS engine.

Now on to your problem, here are a couple of things to work on. Take the cowl off of the plane. It's possible you have a heating issue and removing the cowl can help you figure out if that is your problem. In addition, having the cowl off will make it easier to troubleshoot other issues if it's not a heat problem.

Another thing to check is your carb may have foreign matter in it. When I was reviewing the Great Planes Cherokee I had awful problems getting the engine to run right, and it was having symptoms similar to yours. It wound up being something in the carb. Try back flushing the carb. Remove the high speed needle from the carb, close the carb completely, and pump a bit of fuel into the fuel inlet. This will wash out any foreign matter that is in the carb. Because the needle valve on the 55 AX is angled backwards I think this makes it a bit easier for things to fall into the needle valve opening when you are installing the cowl and have removed the needle valve.

Give these a try and see if this helps

Ken

brett65

My Feedback: (18)

The low end seems to be just fine, it will idle forever and go to full throttle with no hesitation at all, it only took about 1/8 of a turn to tune the LSN. I have not even tried to put the cowel on yet, I wanted to maiden it without the cowel then start trimming it. I may be ahead of myself and not have given it time to properly break in, I did this with my TT 46 complaining that it wouldn't idle. I will try this evening to give it more time to warm up, and start from very rich to ensure that the HSN is not too lean.

RCKen

My Feedback: (9)

Brett,
Make sure you try back flushing the carb as I described above. If you have something in there the engine can do exactly what you are describing.

Ken

bkdavy

My Feedback: (1)

You didn't mention if you are using the stock muffler or a different muffler. We had a GP Extra with a 55ax a couple months ago with a Pitts muffler. It behaved exactly the way you describe. The problem turned out to be lack of back pressure from the muffler. The 55ax uses more fuel than the 46 ax, so its more sensitive to the back pressure. If you're using a Pitts muffler, try plugging one of the exhaust outlets and see if that helps.

Brad

Mr67Stang

I have used two different .55 AX's w/ the pitts mufflers and had no problems with either. This could be an isolated incedent. Not wanting to discredit bkdavy's possible solution, I just do not want anyone reading this to think the pitts mufflers don't work on the 55ax. Perhaps the increased back pressure pressurizing the fuel tank blew some forein debris through the system

I had the same problem with an OS .40la and a back flush of the needle valve assembly fixxed the problem.

brett65

My Feedback: (18)

It does have a bisson pitts muffler, but it is so inconsistent that I couldn't see it being a backpressure problem.