Last week, I picked up a '01 XR400 and after absorbing all the best known methods here on TT -- I tore into it today to give it a once over. My objective was to check the "gordon mods" and to perform the usual maintenance. I did verify that the exhaust port, aftermarket can and desnorkling was done. I feel good about all of the steps I've performed, but I'm having some hot running issues that I'd like to see if I can get some pointers. But first, I'll give the set-up. When I picked up the bike, it ran well - started OK (I wanted it to be better). Here's a list of what I did: Replaced filter with Uni filter (oiled it up first) Adjusted the valves. I think the right term is they were "tight" as the feeler gauge would not go into the gap. Adjusted them to 0.004 intake and 0.005 exhaust. Pulled the carb, did a minor cleaning (very little varnish present in the bowl) - replaced the existing jets (148/55) with (160/60). Replaced Air/Fuel screw with Kouba FS-3 adjustable screw (turned out the suggested 1 1/4 turns per Kouba's instructions (the screw I took out was at 1 7/8) Replaced spark plug (existing was fouled rich) with Denso IX24 plug Changed oil / filter and cleaned screen. Installed K&N fuel filter. Used new fuel (premium - no ethanol) When I was done, it cold started fine, ran fine. Took it for a spin in the snow. Here is where I think I screwed things up. I started to follow Kouba's instructions on dialing in the air/fuel. This was done by bringing down the idle speed and then going -in / out on the air/fuel screw to find the middle between just about stalling on both ends. In hindsight, I think I did this too soon (engine not yet at the right temp). Here's my problem and what steps I took: It was running fine at 1/2 choke (normal idle speed, etc) - then when moved to choke off, it would die Here I adjusted the idle screw to increase idle. Now 1/2 choke was still fast idle, but would still die when choke was "off" Increased idle screw more, but I noticed it would not "hot start" without 1/2 choke. At this point, I increased the idle speed screw even more and it would hold idle at choke off (albiet too slow and rough) This is my first dirt bike and I'm a total novice with regards to carburation, etc. Suggestions? Thanks in advance.