Well, before I explain, I have to say 'thanks" to 2ndcashboy for helping
me to expand my mechanical knowledge. Having worked on cars and
various other mechanical devices for 30 years, I felt pretty confident in
my understanding of certain things. Well, I was only partly correct, and
2ndcashboy straightened me out on the rest! So, here you have it...
Notes on ignition timing:
Lean fuel burns slower (which may be why Super doesn't really help our bikes
much - they're already lean, and the mixture already burns slower!)
(I didn't know this..)
Conversely, richer mixtures burn faster (stay with me here...)
(oh, and I didn't know this either! :shock: )
As the RPMs increase, the ignition module increases the timing advance
(I had ths part right! :applause: ) ...which is why we "curved" our old
distributors with mechanical weights.
HOWEVER....as we put a load on the engine (by rolling the throttle open)
we dump more fuel. from both the jet opening and the accellerator pump,
creating a momentary richer mixture. That mixture burns faster so the
timing actually needs to be retarded a bit (or not advanced as much!) on load/hard
accelleration (had this wrong too! :shock: )
or else you'd get a lot of *pinging* (pre-detonation).
On the VOL and the C50, we have a "3D" timing map, which means that
there is a base 2-D timing curve from the ignition module based solely on RPMS
(and it increases as RPMS go up (again, I got that one right!))
The TPS switch adds the "3rd dimension" to that map by modifying the RPM
map based upon throttle opening (engine load). In essence, the TPS switch
retards the timing (actually, lessens the RPM based advance a bit) to
accomodate the richened state of
hard accelleration or heavy load, then advances it back for cruising.
So here's how it affects the VOL after you do intake mods and a rejet:
You've richened the mixture overall (from the rejet) so you actually
probably need to retard
the ignition timing a tad to get maximum power.
Additionally, since the air/fuel to throttle opening has changed (increased)
you need to get the TPS switch back in sync with the RPM portion of the timing map.
Net result: advance the TPS switch JUST A SMIDGE! to get the map back in sync
and adjust for a richer mixture. (since advancing the TPS means you actually retard
the igniotion timing!) That gives the best performance.
How do I know?
First, I tried full TPS switch advance (major retard - no cracks please! :wink
and lost
power BIG TIME! No pinging or knocking
(as you would expect if ignition timing were actually advanced by this), just crappy power.
Next I tried full TPS retard. Result? *Ping-Ping-Ping!* (don't worry, the test drive was
REAL short! No damage!) which means the timing was advanced.
When I say "just a smidge of TPS advance, I ended up with the switch rotated just
a few degrees ahead of where it was form the factory. I could not see the oblong holes
on the side of the washers,
just the edge of the brass guides (this will make sense when you look at the switch!)
Again, after testing various positions, I feel this is pretty well "dialed in".
Many thanks again to 2ndcashboy for helping me to understand this. In my 30+ years of
fooling with this, I had it wrong (well, partly right anyway! :shock: ) This is what makes this site so
great: all kinds of folks sharing ideas, making everyone better in the process!
To all you VOL owners who do this, I hope this thread helps further your understanding
and performance of these great machines! If you're like me, you just can't stop
messing with it till it's the best that it can be!
Oh, and to coin a phrase, I had it out for 2 hours tonight and it ran like a "raped ape!!" :lol:
me to expand my mechanical knowledge. Having worked on cars and
various other mechanical devices for 30 years, I felt pretty confident in
my understanding of certain things. Well, I was only partly correct, and
2ndcashboy straightened me out on the rest! So, here you have it...
Notes on ignition timing:
Lean fuel burns slower (which may be why Super doesn't really help our bikes
much - they're already lean, and the mixture already burns slower!)
(I didn't know this..)
Conversely, richer mixtures burn faster (stay with me here...)
(oh, and I didn't know this either! :shock: )
As the RPMs increase, the ignition module increases the timing advance
(I had ths part right! :applause: ) ...which is why we "curved" our old
distributors with mechanical weights.
HOWEVER....as we put a load on the engine (by rolling the throttle open)
we dump more fuel. from both the jet opening and the accellerator pump,
creating a momentary richer mixture. That mixture burns faster so the
timing actually needs to be retarded a bit (or not advanced as much!) on load/hard
accelleration (had this wrong too! :shock: )
or else you'd get a lot of *pinging* (pre-detonation).
On the VOL and the C50, we have a "3D" timing map, which means that
there is a base 2-D timing curve from the ignition module based solely on RPMS
(and it increases as RPMS go up (again, I got that one right!))
The TPS switch adds the "3rd dimension" to that map by modifying the RPM
map based upon throttle opening (engine load). In essence, the TPS switch
retards the timing (actually, lessens the RPM based advance a bit) to
accomodate the richened state of
hard accelleration or heavy load, then advances it back for cruising.
So here's how it affects the VOL after you do intake mods and a rejet:
You've richened the mixture overall (from the rejet) so you actually
probably need to retard
the ignition timing a tad to get maximum power.
Additionally, since the air/fuel to throttle opening has changed (increased)
you need to get the TPS switch back in sync with the RPM portion of the timing map.
Net result: advance the TPS switch JUST A SMIDGE! to get the map back in sync
and adjust for a richer mixture. (since advancing the TPS means you actually retard
the igniotion timing!) That gives the best performance.
How do I know?
First, I tried full TPS switch advance (major retard - no cracks please! :wink
and lost power BIG TIME! No pinging or knocking
(as you would expect if ignition timing were actually advanced by this), just crappy power.
Next I tried full TPS retard. Result? *Ping-Ping-Ping!* (don't worry, the test drive was
REAL short! No damage!) which means the timing was advanced.
When I say "just a smidge of TPS advance, I ended up with the switch rotated just
a few degrees ahead of where it was form the factory. I could not see the oblong holes
on the side of the washers,
just the edge of the brass guides (this will make sense when you look at the switch!)
Again, after testing various positions, I feel this is pretty well "dialed in".
Many thanks again to 2ndcashboy for helping me to understand this. In my 30+ years of
fooling with this, I had it wrong (well, partly right anyway! :shock: ) This is what makes this site so
great: all kinds of folks sharing ideas, making everyone better in the process!
To all you VOL owners who do this, I hope this thread helps further your understanding
and performance of these great machines! If you're like me, you just can't stop
messing with it till it's the best that it can be!
Oh, and to coin a phrase, I had it out for 2 hours tonight and it ran like a "raped ape!!" :lol:
