Point of fact: The OS FS .70 Ultimate has no regulator. It's just a pump, at least according to OS. The carb's needles take care of the fuel metering as they normally do in carburated internal combustion engines.
There is more than one seal in the carb, too. A vacuum leak due to crash damage, unnecessary disassembly, or improper reassembly can screw up any motor. Just like a fuel line leak can make any motor "impossible to tune". There are a lot more fuel line connection points because of the pump than a simpler two stroke without a pump. When something complex looking doesn't work the way people expect, or want it to, they usually look for excuses before examining the simple things. Like air leaking into a fuel line where you can't see it...like in the back of the motor.
AS MR. BILL B simply stated above: "The problem is that fuel in the pump/regulator system dries out and you have to turn the engine over a bit to get fuel back into the system. The best way to get fuel back in is to open the carburetor to full, choke it with a finger, and turn the propeller over by hand in the normal forward direction. This will eventually draw fuel into the pump and carb system, and then up, into the cylinder. When you can hear fuel spitting out of the exhaust port, remove your finger from the carb intake and briskly flip the propeller forward through compression several times. Now retard the throttle to just above idle, attach the glow plug battery, and start the engine. The pump needs to be primed, once it's become dry of fuel."
It took me a while to get used to pumped motors, but after learning how to tame my trusty
old HB .40 with the PDP carb and pump, I can do anything, except speak French in Russian.
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','_image/s4.gif')) Maybe it's a case of a leaking pump gasket, who knows? The sell 'em at Tower. I've never taken mine apart, maybe that's why it works.