Vertical dives should be done under full power, too. The max power setting for vertical performance is a no compromise thing with me, a tach helps, tune for max, then back off a few hundred. If your engine is loading up at part throttle, then your tank could be too high with relation to the engine, or the airbleed is insufficient. Muffler pressure usually irons out inconsistent, attitude sensitive running on glow engines. Trying to set up a clunk with a one or 2 oz DUBRO tank is a waste of time, just run a solid piece of 3/32 brass tubing to the rear, and do all the stunts you want, except for inverted flight that lasts over 15 seconds. If you have a hard landing, you will never have the problem of un kinking the flex line, that has pinched itself off when the clunk flies forward, a real time waster at the field.

Andrew, thanks for the tank which arrived safely. I'll have a fiddle and decide on which tank to instal shortly. Maiden flight this coming weekend :O

Unless you plan on making inverted flight the main part of your flight program, a flexible feed line in these tiny engines is unnecessary clutter. They don't consume fuel fast enough to suck 4 inches of fuel dry before the fixed location feed line can get another sip of fuel. If you do mostly positive G type manuevers and flying, your engine will always have a trouble free source of fuel with a fixed feed line. You can still do some negative G flying with a fixed line, but it is best done when the tank is full. Flex lines in small tanks introduce yet one more failure point in the system, with next to nothing in benefit. I make the HAYES 2 oz tanks with a 3/32" brass tubing feed line that is hinged with a hunk of fuel tubing. The solid feed section is too long to swing forward on a hard landing and accidentally pinch the line shut. The SULLIVAN and DUBRO 1 and 2 oz tanks need a clunk that weighs half as much as the engine to swing the feed line, and these tanks are prone to pinching themselves off. With a diesel set up, learning how to make you own tanks from hobby store tin, 3/32" brass tubing and 50/50 solder is easy, and I kind of enjoy doing it. you can cut the tin with scissors, and form it around wood blocks. this way, you can make the tank conform to whatever space your plane might have allocated for fuel storage.

I usualy use a small metal tank with a fixed tube in the rear corner, its good for everything but inverted, in the clunk tanks available in the UK the ones by slec seem the best, the round ones work but i found they turn round till upside down when flying with the vibration

Well I finally found some silicone fuel tubing that works on my Sullivan 1.5oz. and 2oz. fuel tanks. It is GreatPlanes 5/64" Fuel Tubing. 2mm inside and 4mm outside. That makes the wall thickness thinner than usual. The clunks in the tanks now have full movement.