I had found that the pump pressure pulse fittings on the pump and engine needed to be larger with a larger hole though them to provide stronger pulses for the pump. Then the engine, carb and pump started to work good for me. I installed a 8/32 fitting into the backplate on the engine and a 8/32 fitting on the pump diaphragm cover. I then used 1/8 inch fuel tubing to connect the engine to the pump.

Now then after a while, I think the regulator diaphragm and the pump diaphragm became softer and stretched out on me, so I replaced them with better Walbro diaphragms. I suspect our USA pump gasoline will affect the diaphragms after a while.  I used the Teflon pump diaphragm from a rebuild kit and it worked really good for me. The pump/regulator on the engines uses Walbro carb parts, so fixing it is not a problem.  The engine could suddenly start to flood out on you, when that happens, and after cleaning the fuel inlet valve, then you can suspect that the regulator diaphragm has stretched out and isn't shutting the fuel flow off like it should.

Some other fellows had good luck using the Walbro pivot arm on the regulator too, as the stock one is made from a alloy that might be a little too soft, but I haven't had a problem with it. Another fellow found that the spring from the WYL carb (WYJ spring part # 98-3160-7) can help a lot by providing more fuel to the engine too, as it increases the fuel pressure a little bit.

Here is a video of one of my 9cc gas engines on my Escapade low wing plane. I used a OS muffler on the engine to quiet it down a little more.
It actually flies really well and develops good power too. I used a LiFeP04 receiver battery pack and ran the radio off the pack directly and I used a Tech Aero Ultra IBec to regulate the voltage to the CDI unit and also serve as a ignition cutoff switch too. I used a 11x7 prop and regular pump gasoline with Amsoil 2stroke oil (the 100:1 type of oil) at about a 18:1 fuel to oil ratio.
[youtube]http://www.youtube.com/watch?v=0HkMYRiLhPQ[/youtube]