It's got me perplexed

[peabody]

Fooling with this Smoothie....it flew and the engine performed well in January....
I got it down to fly in the upcoming MCRC contest, and it runs from lean to rich......
When it's running lean, the run is terrific, but about 1/2 way through the flight, it begins to run real rich.....not demonstrating enough power to make me comfortable trying tricks.

I see no leaks in the fuel system.....


Thoughts?

Thanks

[Target]

What is the engine and tank setup?

[Larrys4227]

Hey Rich ... are you postiive it's richening up the last 1/2 of run? Could be overlean abit and its getting too hot --- sagging and exhibiting loss of power?

[Dan Berry]

Put in a new plug.

[Randy Cuberly]

Hey Rich ... are you postiive it's richening up the last 1/2 of run? Could be overlean abit and its getting too hot --- sagging and exhibiting loss of power?

Rich,
You didn't give a lot of information but...If it's a uniflo tank system ther are a couple of thing possible and both are linked to leaks in the system.

If there is a very small leak in the tank to the outside the richening can occur when the fuel is reduced enough to uncover the leak.  with no fuel blocking the leak the uniflo resistance to fuel draw is reduced and the engine draws fuel easier and causes a richening of the engine!

The other is similar but can result from an internal leak in the uniflo line like a cracked uniflo tube close to the inlet of the uniflo line.

The first is most likely and I would look for a tiny leak near the inside top of the tank most likely at the front of the tank.

If it's not a uniflo systen I would suspect a bad glo-plug.

Randy Cuberly

[peabody]

Thanks Randy....I had not thought that an internal leak could cause richness....
I'll take it apart ....just for my edification, as I have never successfully re-soldiered a tank....
It was the last of my Smith tanks, too, which I always had success with.
Thanks

[Garf]

If you still have a plastic backplate, check it very carefully. They are prone to leakage.

[Motorman]

maybe it always ran lean to rich and you didn't notice it until the weather changed


MM

[john e. holliday]

Well here's one that no one could give me an answer too(hijacking thread).   I had a vent tube that bolted to the fuselage side on my ARF Nobler which worked great.  But every so often the vent would come unbolted and blow toward the rear of the plane and the old Fox would go super rich.  I would have thought the engine would go leaner.  I know it was rich as you could the oil smoke.  But as stated previously you have a vent problem.

[Pat Chewning]

In my limited experience so far, all of my "weird" engine problems have been caused by dirt/debris in the fuel system -- it collects right at the needle valve or spraybar.  Take it apart, clean it, and the engine runs automatically become consistent and needle is easier to set.

[Tim Wescott]

In my limited experience so far, all of my "weird" engine problems have been caused by dirt/debris in the fuel system -- it collects right at the needle valve or spraybar.  Take it apart, clean it, and the engine runs automatically become consistent and needle is easier to set.

And always use a filter.

[FLOYD CARTER]

Filters are great until they, too, get clogged!

F.C.

[peabody]

I have swapped for a known good tank, ala Ford eek 3....
Have fun!