fishairflow wrote:...half way down - there is no water coming out and there is very little resistance...
The lack of resistance is caused by air in the piston chamber. I find that if I coordinate my pulls with the pressurestat, so that the lever is in the up position and the chamber starts to fill while the heater light is still on, I get more water and less air, and hence the resistance on the pull starts sooner, ultimately producing more shot volume. The pressurestat can usually be coaxed a bit by letting out some steam right before you're ready to start.
Recently I have also started using 4 or 5 micro-pulls during the pre-infusion stage, returning the lever to the top position each time to get a bit more water in. When this works correctly, the final pull starts with resistance and flow nearly from the top lever position. The trick is to work the micro-pulls fairly quickly, as going too slow can produce an over-extracted shot.
Before I started the micro-pull technique, I was using a single pre-infusion pull, and then raising the lever to replace the water before the final pull. But I found that even this small 1/4 pull for pre-infusion can cause problems when the lever is raised. The objective of the micro-pulls is to minimize the vacuum created above the puck, which tends to disturb the puck and cause channeling.