Before I start....I have 99 WR400. I am playing with jetting and am close, but not yet there. My problem (one of them anyway): turning the fuel screw has no effect at all on anything !!! It was suggested that I do the ACV air cut valve mod to regain 'control' of the pilot jet screw as the ACV is constantly adjusting the mixture. This I did. NO EFFECT. Hmmm.... then I realised the ACV mod is for model years 2000 and upwards....yes ?? My understanding is that the 2000 + models do not have the OCTOPUS. It is internal on these carbs and regulated by the ACV ? The 98 99 models DO have the octopus external pipes. So if I block off the hole where the ACV 1/8 inch O ring thingy is, without doing the full Octopus there is no effect?? Anyone confirm ?? So... if I do the full de-octopus I should be in good shape ? Tell me I'm right. Trouble is I cant make head nor tail of the deoctopussing operation described in the tech section. I am totally lost as to which pipes to block off and remove. The only thing I am certian of is how to re-attach the hot start tube. Yamakaze, that pic of your carb would be worth its weight in gold. NH Kevin, can you help too with a clear step by step. Finally, is it absolutely necessary to change the start jet from a WR#60 to the YZ#65 for de-octopussing?