Ole Blue let me down today =-( This one has a few of us scratching our heads

[Paul Taylor]

I got out to the flying field today. Weather was not too bad. Upper 80's, over cast, and a nice breeze at times. I would say it was a good day to fly model planes with the best of friends.
We got started around 8 am.

I put two flights in on my Tutor II, I had replaced the tube muffler for a home made tongue muffler to take weight off the front of the plane. I seem to fly better or maybe it was just in my head. Either way the tongue muffler stays on even if my plane gets a lot more oil on it.

Now for the bad report. I pull out the Vector with the LA .46. FP venturi, OS NVA, metal backplate, running 10/22 and launching at 9800 and some change. The plane would take off fine then go fat for a few laps, then several laps later go lean. After the very first flight I put in a brand new Brodak fuel filter. Next flight was better. It did not go lean but did seem to get a little fat. Like it needed a few clicks on the needle. I landed and next time up, same thing. Fat then lean. I was not running muffler pressure. But in search of the perfect stunt run I put it on muffler pressure. Same thing.  
I spent the whole day chasing a engine run. I was tired and frustrated.
When I got home I pulled the needle and put a paper towel on the other side of the NVA to see if anything came out as I blew it out. Clean. I then blew out the brand new filter and got some trash out. The filter blocked it so I don't know if this could cause the type of engine run I had.

The only change I made to the plane in the past few weeks was to put in a new 6 oz take. The tank was pressure tested before it went in the plane.

The only other thing I know to do is replace all the fuel lines with new ones.

[Paul Taylor]

With a filter having crud in it, it will go lean and stay lean. 

Yea, that's what I figured. But this engine would set fine on the ground at 9800, launch and go fat, and stay that way for some time then go lean.

I told Lou don't bother mixing me more fuel. I'm about ready to go electric if I can not get this figured out soon.

I'm not going to the WKSI contest if I don't get these bugs worked out.

[Wynn Robins]

Yea, that's what I figured. But this engine would set fine on the ground at 9800, launch and go fat, and stay that way for some time then go lean.

I told Lou don't bother mixing me more fuel. I'm about ready to go electric if I can not get this figured out soon.

I'm not going to the WKSI contest if I don't get these bugs worked out.

I wont help then - if it means you are going to go electric !!!! 

[Dennis Toth]

Paul,
Ty hit it, the OS needles can leak air through the back. They are not as bad as the old FOX stunt needles but close. Sometimes they work but temperature changes outside or if the motor get a little warmer and the needle expands and the leakage changes. Change to a PA or ST nva, make sure the lock nut is reasonably tight and that the spraybar is sealed (I always use some silicon gasket sealer between the venturi landing and the spraybar nut) against the case and you should see a big improvement.

Best,              DennisT

[Bill Heher]

You may want to try the old tank and see if the run settles down. Maybee something wrong with the vent /supply piping inside the tank.
You can also slip a piece of fuel line over the needle where it screws into the spray bar to seal any air leaks at the needle.

Good luck

[Paul Taylor]

Thanks guys!
Something to think about.

The NVA has been in this engine for some time and has worked fine. I may end up doing it.

Good call Bill on going back to the old tank. My good friend Zuriel called me this afternoon and told me the same thing. Just to eliminate the tank. Might do that as well.

I do have another LA .46 with a Randy Smith NVA on loan to friend for testing. Might get it back in a week or so and give it a try.

Stay tuned....

[Dick Pacini]

Paul, there have been several good suggestions here and you did some sleuthing on your own.  But I think your initial post has a relevant clue in that the only thing you changed was the tank.  That would be the first place I would look.  Pop the back off the tank and see what it looks like inside.  Inspect the tubes for cracks.  It wouldn't be the first time a new tank was funky.  We did that as a matter of routine 35-40 years ago, usually to notch the baffle and check the solder joints and location of the pickup tube.  Often times a tank was assembled wrong or there were small bits of solder rolling around.  Let us know what you find.

[Bob Hudak]

I chased this problem recently. The problem dodged me for some time. Until I found a small hole in the plastic tank. A fellow flyer had the blues with his until yesterday. His had a break in the uniflow silicone tubing where it slips on the copper tubing(plastic tank also).
          Bob

[Paul Taylor]

Just got off the phone with my coach and mentor.

The old tank is going back in the plane!

[Derek Barry]

In the picture it looked like there was a substantial amount of trash in the NVA. I am sure that it had something to do with the erratic runs. If you have a chance try it again like it is and see if the problem goes away. Another thing to check would be the glow plug, the newer fuels seem to grow taters on the plugs and this too can cause some problems.

Derek