Hi Guys,

Here we go again, after taking Pe's advise, I soldered a tube to the diaphragm cover and ran a line inside the fuse, this is about 20 inches long, and at a spot that I thought would be in still air.
The out come is that the engine behaves a before, no change??? On an 18X10 Prop it is very bad, and can hardly be set. I put a 22X8 Menz prop on and the problem goes away. This prop is however a bit large for the engine and only turns at 5900RPM WoT. Yesterday, we had a holyday and a big fly in at the field, I decided to put the Cowl on the plane and fit the Velocity stack, just because the guys said that that would help. I even cut a hole in the Cowl for the velocity stack. I was hoping that this would do it. I started the engine (it was hard to start) It ran very rich, Max RPM on a new 20X8 Menz was 4000RPM. I thought that it was the cowl that made it run rich so I took it off. It was infact the Velocity stack that made it run rich.
I set the high needle, and it pick up to 7250RPM WOT running very strong and clean, good transition and huge power good idle. So I went to fly. As soon as the plane speeded up there was the surging again, only at full throttle though, I flew a while and landed. I reset the high a bit leaner and flew, the same thing, this time the high end was to lean and it would sag at WOT. I then set it very rich almost 1000RPM below full power, and set the low a bit leaner. The transition got even better, and it now barks at you when you blip the throttle. In the air although no change, it surges at WOT. I landed and set the low as lean as it would go, this improved the transition even further (it's a bit scary now, this thing really barks at the slightest blip of the throttle) and now the high end was clean also at 7200RPM (massive power on a 12lbs plane) In the air, the same surging appears again.
I am at my whites end with this thing, I don’t know what to do.
The engine runs great on the ground, and as soon as I fly a vertical line up, I can actually open the throttle and the surging will go away. At half to 3/4 throttle it performs great in the air and like I said the transition is down right scary. What else can I do??????

Prop Is a Menz S 20X8 well balanced!
Fuel is 95 octane unleaded at 40 to 1 Klotz synth!
Altitude is 6800ft ASL
Engine starts easy, runs very well on the ground, no vibration, idle at 1800RPM and WOT 7200RPM very clean transition.

PLEASE HELP................