Vacuum Lines and fuel pump! I was getting symptoms all over the board from potential timing chain to valve timing to gearbox prolems. Finally got it narrowed down to multiple fuel system problems:
1) Fuel filter & Pump: At higher RPM boggs, it's not getting enough fuel. Take your fuel pump assembly out & disassemble completely. Blow out the plastic housing that encases the fuel pump & reassemble. This solved my RPM bogging issues (mine bogged at 7k RPM). I did a rebuild off of a crashed bike, so plenty of debris in the tank to get rid of.
2) Vacuum lines. Once my bogging problem was solved, it nearly flipped the symptoms to running great at 5k+ RPMs and complete garbage below that, which indicated TOO MUCH fuel. I've read people desribe their bike doing a "Herky Jerky" ...and that's what I'd best describe it as. Anyhow, Pulled apart the air filter housing down to the throttle body assemblies and started tracing vacuum hoses. Sure enough, a TINY hose for the Air Intake Pressure Sensor had pulled loose, so it was drowning the engine in fuel. Popped the hose on and watched it roll coal for about 20 seconds.. good as new. Long story short, apparently when I changed the spark plugs initially, that's when the vacuum hose pulled loose. Bonehead move on my part, but at least it only cost me a set of spark plugs and a fuel pressure relief valve.
1) Fuel filter & Pump: At higher RPM boggs, it's not getting enough fuel. Take your fuel pump assembly out & disassemble completely. Blow out the plastic housing that encases the fuel pump & reassemble. This solved my RPM bogging issues (mine bogged at 7k RPM). I did a rebuild off of a crashed bike, so plenty of debris in the tank to get rid of.
2) Vacuum lines. Once my bogging problem was solved, it nearly flipped the symptoms to running great at 5k+ RPMs and complete garbage below that, which indicated TOO MUCH fuel. I've read people desribe their bike doing a "Herky Jerky" ...and that's what I'd best describe it as. Anyhow, Pulled apart the air filter housing down to the throttle body assemblies and started tracing vacuum hoses. Sure enough, a TINY hose for the Air Intake Pressure Sensor had pulled loose, so it was drowning the engine in fuel. Popped the hose on and watched it roll coal for about 20 seconds.. good as new. Long story short, apparently when I changed the spark plugs initially, that's when the vacuum hose pulled loose. Bonehead move on my part, but at least it only cost me a set of spark plugs and a fuel pressure relief valve.
