wow.....what a weekend. so a while ago i posted about the AP for my yz400. ( http://www.thumpertalk.com/forum/showthread.php?t=424100&parentpage=3 ) no one really had a lot to say about tuning the duration except for the taffy mod. so i decided to check the duration that was currently on the bike and i discovered that there wasnt ANY squirt coming out. so as i removed the carb i proceeded to try and troubleshoot the problem. when i took the AP cover off, i found that the o-ring from the AP supply opening was missing. thats funny, cause ive never taken off that cover before. so i guess joe blow who had the bike beforehand lost the oring. after a quest to find a new one, i finally put one back in. i thought that maybe fuel/pressure was leaking out causing no pump action. so after i reassembled it all, still no squirt. i took it all apart and recleaned all the passages, reassembled and still nothing. by this time i was getting frustrated. i tried taking the float bowl off, filling it up with fuel and while holding it in my hand, trying to see if the AP was sucking in fuel to prime it. well, it was. so now the problem was that it was building pressure but just not getting out of the AP reservior. still couldnt figure it out. so what i did by the grace of a higher power was, build up pressure in the AP and then slowly loosen the AP cover. to my suprise fuel came squirting all out. this was a good thing. at least i knew the diaphram was good. what it did lead me to was the problem. the o-ring that our mr joe blow installed for the squirt passage was a soft clear style o-ring. well, it was just a tiny bit too fat...or it had swelled from not being fuel compatible and when i would tighten down the AP cover the inner diameter of the o-ring would seal closed. this, not allowing the fuel to squirt. so i replaced that o-ring with one a lil thinner, did the taffy mod....and voila. got a 1/2 sec duration and no bog. whew. all because of an o-ring the diameter of a pencil. so i rewarded myself wit an 80 mile desert ride in prep for the Las Vegas 300. woo woo!!