Went out on the Grenade at the weekend and found it pinked like a fatherless child at high throttle openings and low engine speeds. I was baffled, until I thought back to what had changed recently...
...During a regular 'once over' on the Grenade, I found the VOES looking a little tired, the wires exiting had lost their insulation, so I decided to change it out for a new one...
People are probably scratching their heads wondering what a VOES is. Well, it is on all carbed Buells (and Harleys) and is a Vacuum Operated Electrical Switch, which tells the ignition unit which curve is needed. With a depression, such as the throttle closed, the switch makes contact and a curve with more advance is selected. When the throttle is opened, the depression goes away and the switch should then break the circuit and a map with less advance is selected.
As everyone knows, you need more ignition advance if you have a diluted (closed throttle - exhaust gases are sucked back into the cylinder during valve overlap) or lean mixture. In both these situations, the mixture is burning slower so you want to start it burning earlier. The other time you want more ignition advance is at high engine speed, where the charge has a shorter time to burn, so again, you start it burning earlier.
As everyone also knows, an over advanced ignition, especially in big bored engines, can lead to knock or pinking at large throttle openings and low speeds, hence when you rip open the throttle you want less advance.
Back to my problem and it looks like the new VOES has a different (higher) trigger pressure than the one before. I did a bit of reading up and found lots of articles about how they tend to differ in trigger pressure out of the bag. I also found that you can pull the silicon sealant out to get to the adjustment screw with a little hook... Before...
...And after...
The screw controls the preload on a spring which essentially changes the pressure (depression) at which the contact is broken. At the extremes, if the screw was removed, you would always have the curve with the higher advance. If the screw was screwed in all the way, you would always have a lower advance curve.
Looks like I need to screw mine in a little, but how much? Well that is where some monitoring of the switch position comes in.
I have produced a slave harness:
And connected an LED in series with the switch:
This will allow me to see when I am on each curve, when the LED is on I am on the higher advance, when the LED is off I am on the lower advance curve.
In addition, I put a longer bit of hose on the switch so I could hang it onto a frame rail for easy adjustment:
And more importantly, I need to seal the top of the VOES again to ensure no leaks down the screw thread. I will do this with some insulation tape or similar.
Back to the ignition timing, I am going to need to have less advance when I crack open the throttle, so I will be watching the LED when I do this and it needs to be off... But at cruise, where the mixture is diluted, I need the LED on. And back to the ignition curves above, I am using curve 4, I will want the LED on at part throttle up to 5000rpm. However the plan will be to get rid of the pinking and see where that leaves me...
That is a job for tomorrow though...
PS. This is nothing new, I had the idea of what to do, but then when googling I have found that every man and their ferret has done it already...
Nick 
no not the one to stretch me dong 
....pat pending ?.....I really dont think so, some of us have been doing this stuff for years 
says, not new by any means, just a challenge set by original part variability that I have not seen anything posted about here before.
