Well look at it this way. With 3/4 tank, cap on and the vent hooked up to the rollover valve mine will flow about 26 ounces/minute from the petcock. With the carb
bowl off, the float at full drop and the pump running the most that will flow through the float valve is between 10 and 12 ounces/minute. That's why I stated that the petcock will flow more than the carb will use.
And yes the Grizzly valve is the best because it has the largest opening (3 mm
)anyone has found for the stock carburetor. The 42's use a 4.2 mm opening for pumpless use and I wish there was one that size for the stock carburetor out there somewhere.
Others have stated that they can see the air at the top of the fuel filter and haven't had any problem running the tank dry. Without the filter mine would always run dry at just under 1/4 tank with the petcock in the regular position. I put my pump back on before I found out about the filter thing but plan on taking it back off this winter.
The other thing I had to do was raise the float level up to between 5 and 6 mm's above the bowl seam to get the running level right. The reason for that is because the float has to drop farther to provide the same flow rate at speed than it does when the pump is hooked up. Obviously the pump can force more fuel through the very small opening when the float first opens the valve than gravity can.
It's true that cutting some off the stand pipe will allow more fuel to flow from the tank but it also means that there will be less fuel left for reserve. It doesn't cure the problem.
You can try it with the rear spring set at the full 2" preload if you want but from my experience that's a really rough ride. I like the fuel filter fix the best. And 45 degrees on the filter is probably fine as long as the air can gather at the top and flow back up to the tank. The trick seems to be not to let any air get into the line to the carburetor.