As posted ealier, make sure you have large (1/8" ID) fuel tubing from clunk to carb.
The symptom you are describing sounds like the motor is starving for fuel.
Don't fly it this way!

If the tank is close to the engine, respectfully suggest you leave the Cline off to start.
Get the engine running good without the regulator, then put it on.

Let us know how it works out for you.