My 25 LA has a metal backplate and front NVA. Hauls a Pat Johnston Stunt Trainer around.

Was pulling magnificently until I got to the last corner of an inside square. For one reason or another it was a bit tighter than originally planned (the ground was in the way), and the engine "burped" about half way through. Made the corner, but the engine didn't recover to the smooth note for the rest of the flight. Speed/line tension down for the rest of the flight, but still enough for a few wingovers.

I'd run a tank through a few minutes earlier with no problems, and the previous landing was as perfect as my flying patch allows.

To my ear it sounded like the engine had leaned out and just never recovered.

Any suggestions?

I had been having some problems with consistent runs with this motor, so I re plumbed the feed line, to remove all sharp bends in the silicon tubing, and it did appear to solve the problem. Tank was flushed/washed and pressure tested after rework with no leaks (or rattles). I had also cleaned/flushed the complete fuel system recently, and this mornings fuel was filtered between can and filler bottle, and tank and engine. Tank is a home made uniflow.

My tutor has suggested maybe a different plug (after first suggesting an Enya 30), as I'm using the plug that came with the engine, and to check the fuel line for pinholes. Any more advice?

Lou,

Thanks for the suggestion, but no good this time.

The tank is a home made metal uniflow. Tank is the "standard" house shape, with feed pickup at the back corner (apex). I've always vented my uniflows to the apex at the front of the tank, and this one is no exception. Mind you the largest I've needed up to now was 50 cc (~2 oz)

The change I made to the plumbing was to angle the feed line down, once it left the tank to remove a potential tight spot on the silicon tubing. i.e. 30/45 degree bend aded to the fuel feed line, on the outside front face of the tank, to give plenty of clearance for the cylinder head.

It seemed that on earlier flights I'd had a kink in the silicon tubing where the feed line exited straight out the front of the tank and the silicon had to do all the bending.

I'm feeding silencer pressure to the uniflow vent.