Hi all
I have a problem with my os. 40 fp going lean very quickly, especially in a nose up attitude. I have had this checked by MANY experts and they have all come to the conclusion that it is not the tank and lines, so please don't go down that route, the problem is that the engine isn't great. My question is, would a one way pressure valve or check valve between the tank and muffler help supply a constant pressure of fuel to the engine? Thanks
Gareth

If you say the engine is not great and you want to spend extra on trying to cure it, would not the best solution be to get a brand new one or a NIB off ebay?? Just a thought.

Pressurising the tank will not solve your problems because the pressure will be inconsistent ... causing problems with fuel supply.

You would need to fit a regulator between tank and carb. There are several regulators on the market.

Alternatively, you could fit a Perry pump to the model. These work well and reliably, delivering a constant head to the carb.

Alternatively, alternatively, you could adapt a Walbro carb to provide a regulated fuel supply for your carb. This is easy to do ... once you know what you are doing!

My advice would be to either buy a better engine or else buy a Perry pump.

G'day If your engine is tired, perhaps as the previous poster said, you should consider a new engine. Having said that, more castor oil in your fuel mix (as much as 25%) can help increase compression and sealing in old tired engines. It is not a cure but a bandaid though. Plain bearing (bushed) engines like the FP and LA series like castor in their fuel mix.

Could you have a crank case leak? This too will reduce the efficiency of the engine.

Is the plating on the liner still in place? The LA and FP series are noted for wearing through their Nickel plating. I have a low time LA that is totally useless because of this. It was probably used in a dusty environment.

Mike

There really isn't anything else that will cause it to go lean if the fuel draw at the spraybar is good.


I have about a dozen .40fp and clones, magnum, tower, etc. I use them in funfly planes that gets tossed around plenty, never had a problem with the engines going lean.

Keep your tank positioned very close to the engine, is all I can offer.

Should you consider buying a replacement engine, new or used, please consider the Thunder Tiger GP-42. It is more powerful than the O.S. 46LA, user friendly and less expensive. Remember, if you buy it new, that it REQUIRES break-in. Your idle and top speed will both be affected. Be patient for a couple of hours and you'll be rewarded! I have two of them, both of them behaved the same way, both are a pleasure to use...
Beppe

No, it would just make the idle run lean after adjusting and running at idle for a lenght of time. It would trap the muffler pressure in the tank when the engine drops to idle, making it run rich, then you adjust the idle mixture to compensate. Now it idles great, but when you taxi you model out it leans out and quits because the tank pressure slowly drops.

Gareth,

What makes you think so?

It sounds to me as the low pressure at the Venturi is diminished by air leaks thru other points of the crankcase.

In nose up attitude, that marginal low pressure at the Venturi cannot pull enough fuel from the spray bar.
May be the muffler pressure that the tank feels is not high enough; do you have the factory diaphragm in it?

I would cover the carb and sumerge the body in water, then blow thru a hose connected to the exhaust.
Most os the air leaks are reparable, except the ones thru the flat bushing-bearing.

Just a quick test before quitting on the machine.

Hi!
Please post a picture of your set up!
It's very difficult to give any advise without seeing the plane/engine combo.

engines are disposables.
If no matter what, replace it! Saves you a lot of grief. If the new engine still has the same problem, get rid of your "experts"

I'll betcha 50 cents its the air bleed hole. This has been discussed many times here with the same symptoms, heck I even wore a small indentation in my onion with the same problem.
You most likely can correct it all by taking the carb apart and cleaning it with attention to the bleed hole and setting the bleed screw properly.