xsryder

Hi group, I am a huge XS1100 fan, and have owned, maintained and restored several 1979 XS1100s. I like the 79 model because of its reliability, styling (decals) and kick starter (for praticality rather than machismo). My current XS11 is a 1979/80 hybrid. Two years ago I bought a running 1980 bike primarily for the engine, seat and tank, and had it fully serviced, including carb overhaul and cam chain replacement before I totally dismantled it, and have spent two years building up a fully restored machine pulling together the best parts of several bikes. The roblem is that since I finished the rebuild, the engine runs out of steam at about 110kms. The strange thing is that the machine goes like a scolded cat up to that speed, but then feels like it has run out of gas. The local Yamaha dealership have been working on it off and on for three months, and have thrown in the towel saying that they just can't pin-point the poblem. I have fitted new inlet manifolds, new carb diaphragms, carbs overhauled and balanced more than once, plug caps changed and timming light shows seemingly correct advancement. It idles nicely with good throttle response, and the drop of the clutch is as exciting as ever, especially with the sidecar attached because the home-made wheels are considerably smaller than the standard 19" alloys and the altered gearing easily lights up the tyres. But as soon as I get to the outskirts of town and my speed increases to around 110kms, the engine loses power and I am forced to pull over and wait for revs to rebuild before I can continue. The engine doesn't miss-fire or blow smoke, and has good compression across all four pots. The engine is in good condition and set up as a sidecar has gone over 170kms/hour and has been timed at 15.5 seconds quarter mile (with out second gear). There is something very simple preventing this engine performing as it should, and the local Yamaha dealership and I have run out of ideas...can any one help?