I have a pretty new(2months)o.s max 46la which was broken in according to the manual. My question is this...Whats wrong? After about 5 minutes in the air i loose power for some reason.. I end up having to land the plane. Am I running too rich or too lean maybe?

I am most definitely NOT an engine expert, but have many years of meesing with them. You didn't mention how many times the engine has been run/flown, but I suspect that it may still be "breaking in. If so, it needs to be run a little rich. Many flyers, and especially rc newcomers, adjustt the needle valve for absolute maximum rpm on the ground. When the load on the propeller lessens in flight, the engine speeds up , leans out (not getting enough fuel/oil), gets hot and quits.

I haven't had a .46 LA, but I am currently operating four OS Max 40 LAs (covered in the same OS operations manual as the .46), on two twin-engine planes. Each of the engines was broken in on a sport plane, and took about 10-15 flights (two hours??) of running before they could be flown near peak rpm. On the twin I always keep the engines just slightly richer then peak.

Some things to check;
1) are you using the recommended size propeller - 11 x 7 (a smaller prop could have the engine running too fast...and lean)
2) before taxi and take off are you peforming a full throttle test with the nose vertical? hold for at least 5 secs, rpm should stay constant and about the same as when level. Decrease in rpm indicates you are too lean, while an increase indicates too rich. The greater the rpm change, the more you will adjust the needle valve setting.
3) can you feel oil coming from the exhaust (its hot so hold hyour hand a few inches behind the muffler outlet), and/or is there a visible exhaust trail behind your flying airplane? if not, you are probably too lean on the needle valve setting.
4) does the exhaust have a lot of black residue? This occurs some what while the engine is breaking in, but a lot of black indicates a lot of aluminum wear and generally indicates the fuel-air mixture is too lean.

I hope something in the above is of some help.

Really need more information. Like how enclosed is the engine? Where is the center line of the fuel tank with relation to the motor? Are you using the right glow plug? Try a new glow plug bad glow plugs can do some strange things. Is the fuel foaming? Do you have the fuel tank padded? How about the clunk? Have you made any hard landings? Like nose into the weeds. If so check the clunk it can get forced to the front of the tank and lodged there. How large is your tank? What size prop are you using. Try a different size? Have you tried a richer or leaner?

All kinds of possibilities for the cause... but it SOUNDS like you are running lean.

A hard to locate cause is a pinhole in the flexible line inside the fuel tank. The fuel level in the tank goes below the pinhole and suddenly the engine won't run right. Runs fine with a full tank ever time. This one can drive the local engine expert nuts. (and its a good reason to have the ability to easilly pull the fuel tank from any model.)

Dirt in the fuel system tends to accumulate inthe needle valvve is you don't have a fuel filter. That will make the engine go lean. (but it will be impossible to retune it and make it work until you clean out the needle valve.)

A split muffler pressure line can make the engine run lean... and it will get worse as the fuel level goes down.

Too heavy of a prop can make the engine run hot... too small or too large is not good, but you can adjust the fuel mix to prevent overheating with the undersize prop easier than with oversize.

*****

My bet is a fuel line problem. 5 min is too long for it to run properly with the wrong size prop. It is also too long for it to run properly with an excessively lean fuel mix. Sounds like its running too well and consistantly for it to be dirt in the needle.

yeah it happened on my last couple of flights, and the engine is still fairly new only had about 15 flights on it. I have an 11x7 prop. The plane is a kadet lt 40. There is black on the front of the rudder after a flight. I dont really see any smoke coming out of the exhaust during flight, just when i am testing on the ground. It kinda sounds bogged down when i loose power.

I'm almost positive that you are trying to run the engine too lean. You can not tune it for maximum rpm on the ground because our engines get a bit leaner in the air as the prop unloads and the fuel tank level gets lower.

That black on the rudder is probably metal shavings from your engine mixed with oil. Definitely not a good thing. []
Dennis-

I have the same engine. Sounds too lean. More importantly you're wasting you time even trying to adjust it if you don't have the right fuel. I found I had to run the green Cool Power 15% Heli fuel to get my to run consistant. Yes I said heli fuel. You could adjust it all fricken day long and it would go out of tune on the frist flight if the engine doesn't like the fuel. The the fuel I just mentioned it run great with to tweaking required.

Does somebody know what so special about the heli fuel?

thanks for the info. I just bought a gallon of 15%. I am finishing up some 10% first...

If you are only going to change fuel the higher percentage will only make it run hotter. If it was me I would go to to a smaller prop. I only run 10 x 6 on my .40's. I don't really think the LA 40 has the horse power to properly turn an 11x7.

I agree with A.J., there is no way that your LA will turn an 11 x 7. I use to turn a 11 x 6 with my FX of the same displacement. I would suggest you go with 10 x 6-7. Running lean will get you in trouble but anyone that has tuned an engine should be able to run it right without having it lean out.

I think the cooling could be a problem. If you have it in a full cowl, it will overheat. Use to happen to my engine all the time!

First thing, though, try a smaller prop and ensure there is good cooling!

I didn't mean simply 15%. The last fuel I was using was 15% as well and the engine ran like total crap... if it stayed running at all. For me it was that exact brand and type. Green Cool Power Heli 15%.

Oh and follow the instruction exactly to tune the top and bottom end. EXACTLY. Don't use some other method.

I have a 46LA and it runs very well on standard 10% glow fuel.

The 11X7 prop is a bit too much for the engine though, try a 10X6 or 10X7.
Dennis-

thanks for all the info guys i will try and change out the prop before i change the fuel.