Hi All! It's been several years since the trusty steed's last let me down, but that day's come. Anyway, here's the problem... AFTER a rebuild of my stock 1972 XS2 carbs (rebuild kits from Mikes XS), the bike idles perfectly, but goes flat (severe hesitation) when engine speed is increased beyond idle. This happens BOTH under load (i.e., attempting to ride) or just revving the engine out of gear. If I engage the cold-starting choke (enrich the fuel mixture), it'll then rev properly out of gear (no load), but still goes completely flat under load (attempt to ride). So I think it's safe to say that something's causing one or both carbs to be running too lean. But I've been through the carbs so many times since the rebuild (which I've done many times over the years without issue) without finding any problems or making any improvement. At this point, I'm thinking it's gotta be something simple/obvious that I'm just too worn-out/confused to see. A bit of background... The bike had been running perfectly until this year. Due to scheduling and life, the bike's spent the past year sitting in the garage, without use (tank full of premium unleaded, petcocks off). When I finally took it out last weekend, it'd developed an INTERMITTENT flat spot under load (i.e., idled and revved great, but INTERMITTENTLY hesitated during acceleration and/or when maintaining ~40~50 mph). Oddly, I noticed that, again INTERMITTENTLY, if I let it sit and idle for ~25 minutes, the idle would suddenly increase to ~1,500 and become perfectly smooth. Then, the flat spot was GONE. A few nights ago, after this happened, I took the bike out for a long drive and it ran perfectly! But, the next day, the flat spot was back. So I figured there was either tarnish or debris blocking one of the carb fuel journals and Seafoam might clear it. Unfortunately, the Seafoam didn't help. As this flat-spot problem had happened previously and was remedied by a carb rebuild (with kits from Mikes XS), that's what I did this time. AFTER the rebuild, the bike started right up with a perfect idle, but it was now CONSTANTLY going flat--no more INTERMITTENT!--at anything beyond idle. Just to cover all the bases.... I just replaced the NGK plugs with same NGK plugs, but that made no difference. I've checked the petcocks/fuel lines, but both're clear and flowing great INTO the carbs. I've replaced the float bowl fuel balance tube, which was clear. Again, the only thing that changed between the INTERMITTENT and CONSTANT hesitating was the carb rebuild. So it's gotta be carb-related. This sounds like a classic fuel starvation issue, but I'm completely confused as to what to do now?