Was traveling on the Interstate the other day at around 80 MPH and felt a slight surge I twisted the throttle and it seemed as if there was nothing left to give. I backed off and twisted the throttle again and the power was there no problem. The surge contined several more times at high speeds did not notice and problem at lower speeds. ANy suggestions on what might be going on inside those six cylinders?
It's possible your petcock diaghram is beginning to fail.
My diagnostic suggestion above could be wrong, but I spent a long night in Las Vegas, NM researching petcock failures after the bike quit working on I-25 and had to be towed. My earliest symptoms were similar to yours and they got progressively worse until I experienced total failure of the bike to run.
According to posts in both the Tech Forum and Tech Archives, two factors come into play:
1. At high speed/RPM, the fuel delivery is near maxed out relative to demand by the engine.
2. Vacuum is reduced at higher RPM.
Since the OEM petcock operates by vacuum pulling open a diaghram, at higher speeds any leak in the diaghram will not allow the diagphram to open fully, reducing fuel flow.
When I took mine apart, it didn't look bad, but in fact there was an area at the center of the diagphram where the rubber had eroded from the mesh it is embedded in, producing a substantial leak at high speed.
The above petcock was 12 years old and had about 60k miles on it.
To test the diagphram, turn the petcock to the 'off' position and remove the fuel and vacuum lines from the petcock. After the intial residual gas from the line is gone, fuel should not flow or drip from the petcock. When you turn the petcock to 'on' or 'reserve' and fuel flows, the diagphram is definitely bad. If it leaks a just a little, it's on its way. If this is the case, you can rebuild the diagphram side of the petcock using a 'cover' set that's available for about $28 from HDL Parts.
I usually take the extra step of using a piece of windshield washer tubing and attaching it to the vacuum port on the petcock. You can apply a small amount of vacuum by sucking on the hose. The petcock should not flow fuel in the 'off' position, but should when turned to 'on' or 'reserve'. If fuel flows in the 'off' position with vacuum applied there is a problem with the spring-and-ball part of the petcock and the whole assembly should be replaced.
An alternative to either repair mentioned above is to install an aftermarket petcock such as a Pingel. Propoents of both approaches abound here.
