I flew up to my country place in the Catskills from my home base, Long Island's 1N2. We landed at Freehold 1I5 and tied down. My buddy picked me and my other friend Steve up and we spent a few hours at my place. It started getting grey so we decided to head home. Steve and I got dropped off at freehold at around 1:00pm. Untied the plane and took off for home. My plane is an RV-6 with full dynon Skyview system. I also have a backup steam airspeed, altimeter and a compass. My thinking was that if the entire electronic system went poof, I could probably get home on steam. Anyway, when we were taking off on the grass I noticed that the stall warning was screeming like it never had before. I mean beeping way more than normal. I chalked it up to taking off on the grass, and once we were off it stopped and we started climbing out. As soon as we got to the end of the runway we started hitting light rain. Very light rain and I let it climb to around a 1000ft and throttled back. I have a wood prop. I didn't want to damage the prop in the rain. We were climbing slowly and I headed home. I could see the weather was clearing ahead so I kept it throttled back and continued on. I noticed that the airspeed seemed very low like 100 knots, but figured it was because I was throttled back. I usually don?t fly that way on a trip like this. I was climbing slowly and had the autopilot set. All was well but it seemed much slower than normal even though I was throttled back. It looked like a nice tail wind because we had a ground speed of around 135 even with an indicated of 100. The trip is about 109 nautical, around 45 minutes. Steve fell asleep, I was up to 5500 ft cruising along and all of a sudden I hear CAUTION in the headset and the plan dives. I look at the screen and it's saying speed too slow, or some such thing. Steve jumped up and the airspeed indicator went from 90 knots up to 145. What the heck? I hit the auto pilot cancel button when the plane dived and wasn't sure what was going on. What we think happened was something crawled up the pitot and partially blocked it. It must have either blown off or back into the tube further and cleared. The rest of the trip was uneventful. Luckily it cleared, I don?t know what I would have done had it still been blocking the pitot. I did hit the cancel button and level it off before I even looked at the screen. But had it been reading stall and I was really not? I thought I was so cool having backup steam airspeed and altimeter but guess what if both are fed from the same pitot you don?t really have backup. I looked at the log file and you can see where it dives and the pitot clears and the airspeed jumps from 90 to 150 knots while the ground speed goes from 138 to 150. I haven?t gotten to taking apart the pitot and lines, but I will before I fly again.