Jack some from the EBU 2 machine shop 

Well I got around to adjusting the Throttle Position Sensor.

What prompted these adjustments was my idle being too low. Suzuki says my sv650 should be idling at 1300 rpm +-100 rpm. Mine was at 900rpm! Now wonder that I stalled out a light the other day. Anyways that was a very easy fix: warm the bike up to operating temperature (I just waited till it got up to 190 F)
and then adjust the idle adjustment screw. After adjusting the idle to a proper 1300rpm I could mess with the TPS. 

Now at this new benchmark idle rpm, I was able to determine that when I turn the throttle, the main fuel injectors engaged at about 2900 rpm. This was done by connecting a wire to two terminals in the dealer mode activation connection. Basically, your motorcycle is not just a hunk of metal and some wires and rubber. All those voltages tell you important information. Even more, when you connect the dealer mode "tool" your display turns into a diagnostic display. I never knew that, which is pretty awesome to find out. Anyways, the whole process involved turning the throttle and the display on the screen would change. You could find out the specific rpm by watching the tab change position.


Notice the bar change from center position.

The center indicator is the key to adjusting the TPS.

I adjusted the TPS by unscrewing two of the security screws on the actual sensor. You then adjust it by rotating the sensor. It was very delicate and I only had to move it barely half a millimeter to change the rpm response from 2900 to 1500rpm! Once again, you check that using the screen display. Turn the throttle and when the bar moves up, it is at that rpm. (Instead of having to turn the throttle to 2900 rpm for the bar to go up, I only turn it to 1500 rpm and the bar goes up!)

If you think about this, this explains why the torquey sv has that lifeless feel in all the low rpms. It is because fuel is injected as per command of the TPS. Now that the position is lower at the 1300 rpm idle to 1500 rpm, it only takes that 200 rpm to get that fuel injected power. This is verified in the test ride around my block. The throttle feels like one of those "dimmer" light switches compared to the previous "on off" light switch. It feels much smoother, shifting and everything. It feels like I get to redline faster which is something i'll have to check as I ride more but I think it is just all in my head.


A couple more things: Now that my bike is injecting more fuel at a lower rpm, this will affect my mileage i think. One guy that did the TPS adjustment said his fuel consumption went up: he got 52 mpg instead of 55 mpg. Basically, the argument is 1st and 2nd low speed drivability improvement vs. 3mpg. Which is more important? I have yet to ride a lot so I can't answer, though the low speed maneuvering is nice! Doing a u-turn, I have to do MUCh less work with the clutch! Anywho, I keep very good track of mileage so we'll see the next month or two how this affects my mpg's.

Engine braking is a little different after the TPS adjustment, don't know how to explain this yet either. To me, it makes sense that you save gasoline when you engine break. It has to do with the engine applying force on the drive and ultimately the wheels and ground. Apparently it has to do with throttle mechanics and how the fuel is injected to keep the engine pumping!

Moving onto the topic of factory settings: why did suzuki adjust to a certain rpm? Many speculate emissions control. It would make sense that to meet the requirements of agencies, reducing sportability for the sake of emissions would be one way to go. Thus the TPS adjustment is most likely one of the things that the corporation took into account because it specifically regulates fuel injection. This starts to come togehter if you really know how the system on the motorcycle works: fuel injection and throttle as applied to thermodynamics/physics.

This whole adjustment taught me much more about my motorcycle but likewise opened up that many more questions. I tis important to think of this whole project as exactly that: it is an adjustment. Whatever the results are, they are solely up to preference and performance. Finally, I want to leave off on the note that I am open to all comments and criticism! I simply hope to learn more about the workings of the motorcyle.

So my gasoline light flickered on at 166.3 miles yesterday (I need to fill up later this morning). That is pretty good considering the indicator light goes on at 3.00 gallons. This is showing me that the adjustment to the sensor didn't affect fuel consumption, that much. The only other way to explain this actually slightly better than normal gas mileage is that I guess on this tank I really lucked out with timing green lights. Likewise, my 8-9 am rush-hour lane-split speed has gone up and I find myself splitting at 35 mph normally. Disclaimer: I do not ride like a grandma haha. Red lights are a joy and the tachometer on the clear freeway is almost always 5600rpm @ 75mph. 

But that is insignificant. The main thing I feel with the SV is the improvement in turns. Before, I entered the curves with a little hesitation. Now it is all rubber on the road and full steam ahead into the turns (in my 20 minute commute that would be the on ramp to the I-5 on the way back home.) With the TPS adjustment, I do not hesitate in the turn at all either. Throttle response is very smooth and very precise! As an example, before when I was riding on the onramp or (Palomar twisites) a little hesitation and a rolling off the throttle felt very uncomfortable. I would roll off the throttle and the bike would feel as if I was rolling in neutral till the next second when the throttle was increased again. Now I FEEL the turn and engine working together and the slightest flick of the wrist is always there for me.