An experiment: Tuning out last of the "shaking" via throttle grip metrics and PC V Map
Many of you know that I am currently working to eliminate the last of the "shaking" that the VTX 1800 commonly exhibits in the 1800 to 2300 rpm range, especially when there have been exhaust and intake changes made.
I have had the bike dyno tuned via Power Commander V ("PC V"), which made a big difference, but did not eliminate the shaking entirely. Micah Shoemaker, my dyno tuner, explained that tuning in that rpm range on the VTX via normal 4-gas method does not seem to work as well as it should (worked well every other rpm range), probably because there is an exhaust or intake resonance. Even the Cobra "PowrPro" autotuner was unable to eliminate it - the Cobra PowrPro exhibited notable loss of control of AFR in that range. Micah suggested I "hand tune" by manually modifying the Power Commander V fuel map manually via road test based trial and error.
The first step was to "calibrate" the throttle grip so that I could know what % throttle I was applying at all times. By doing so, I could know, every time I got the shaking, exactly what combination of engine rpm and % throttle it was occurring at.
The following photo shows how I did this:
The concept is simple. I put a piece of masking tape (masking tape as sued by painters, so that it can later be removed without a permanent residue being left in place) on the grip itself, and marked a "pointer" in ink on it, at a point that could easily be seen when riding the bike. I then also put a piece of masking tape on the grip housing, with a zero to 100% scale that could easily be viewed when riding the bike. By using these 2 pieces of tape, I know exactly what percent throttle I am applying when the shaking occurs. My Cobra tachometer gives me the engine rpm. So, I now have both rpm and % throttle.
As I discover rpm / %throttle combinations that exhibit shaking, I hold the combination as long as road grade and wind conditions allow to verify it is non-transient, and make notes on a notepad I carry. When I get home, I fire up my PC V software, and modify the fuel map to try to reduce or ideally eliminate the shaking at that point.
What has been working is richening the air fuel mixture at that point. You do this by increasing the percent of fuel increase within the body of the PC V fuel map, at that specific combination of rpm and % throttle. As you address more and more of these, the shaking becomes less and less frequent. This makes sense, because virtually all modern bike engines run lean from the factory for emissions reasons, and aftermarket exhaust and intake makes things worse due to more airflow beyond factory airflow. In the one book I have found devoted specifically to MOTORCYCLE engine EFI tuning, the author uses a Yamaha example where the mixture needed to be richened by a full 15% with STOCK exhaust and intake, in order to run like it should.
I now have gotten to the point where the shaking is almost entirely gone. It occurs now only specifically within a range centered on 2250 rpm and 20% throttle. It is detectable, although with far less intensity, as low as 2000 rpm and as high as 2500 rpm, and within the 15% to 25% throttle range only. It does not exhibit at all in normal level road cruising without notable headwind, but manifests only on uphills, headwinds or acceleration, because normal cruising at 50 to 55 mph in 4[SUP]th[/SUP] or 5[SUP]th[/SUP] gear does not require getting up to 20% throttle. Once I hit the 20% throttle range, I can still feel the shaking, although greatly attenuated from before. This appears to be the sole remaining sore spot.
So, last night, I richened that remaining range just a bit more (5% more), and will see this Saturday if it makes the necessary difference. (It is way too hot now here in Texas to go riding after work on weekdays - 98 to 102 degrees typically).
I have noted that the largest % increase in fuel that I need to apply was 42%! That needed to be applied to only 2 or 3 cells, but naturally tapering was required from there back down to the lower percentages developed around those points, on the dyno.
I'll let everyone know how this latest change works out, next weekend (unless it rains).