TPS adjustment,Octane info, jetting Help, its all here!!

[rider123]

I'm hoping that my experiences with fooling with the mixture screws and TPS adjustment may help some of those guys out there looking to smooth out their bikes or get rid of some of the horridness of the stock jetting. From the factory everything on my bike was either out of wack or not set correctly. Here is my reply to help some other gentleman on this board and I hope it may help some others out too so they don't have to fiddle for days to get things running smoothly.

Here is the reply:

You could try the mixture screws if they're drilled out. For example I've been fooling around with my mixture screws these last couple of days to further fix the screwed up jetting from the factory.

For example on my 2005 Bandit 1200 with stock everything:

temp 9 degrees celcius, nice sunny day.


Haynes manual standard turns out 3.0

At 3.0 it works but is horribly rich, I can smell it when idlling at a stop light and not fully warm. Fully warm it idles ok and not so much smell, but very mushy down low (too rich)

2 1/2 turns out I'm getting it to idle ok but definately too lean, not too mushy down low but a bit and a little surging at cruise rpm and slight hesitation.

2 1/2 and 1/8th out is perfect but when it gets super cold and clear it gets slightly lean again.

I have it now at 2.75 turns out and it idles fine and not mushy at all. However it's still cold so when it gets warm out I'm probably going to have to lean it out slightly in summer temps >15 degrees celcius. Probably back to 2.5 and 1/8th turn out or so. I may just turn in the screws and extra tiny touch to see if it gets even a little better for fun. But remember its winter so when hot humid air comes along it may be a tad rich.

Also, Octane for me helped alot too. I was running 87 Octane and down low with larger throttle inputs, when fully hot, I was getting some pre-ignition and idle was rougher. I had a half tank of 87 octane and filled the rest up with premium at 91 octane and there was a huge improvement. The effective octane rating is around 89 or so. I know that mixing grades is not good so I will fill up next time with premium and then try 89 octane to see if it's ok. 87 on my bike is too low. Fuel milage rose dramatically and I got a bit more "snappyness" as well when increasing octane levels.

This may have something to do with the TPS sensor that advances the timing based on throttle inputs. When I got my bike it was set from the factory "lazy", meaning it wasn't giving much advance at open throttle inputs. When I set it correctly according to the Haynes manual it really helped alot with the throttle response so it must be advancing the timing correctly now. However as you advance the timing you are going to need slightly higher octane or you will get pre-ignition like on my bike. I don't think this effects the older (<2000) B12's as they dont have a TPS. It also explains why the newer Bandit's get slightly better milage as the combustion will be slightly cleaner and more complete when the timing is slightly advanced on open throttle positions.

[ray nielsen]

The TPS circuit "tells" the ignition module how much load (throttle) you're applying and it actually retards timing a bit to prevent pinging.  The transmission switch "tells" the ignition module which gear you're in to allow the module to "select" the correct advance curve.  Separate curves are used for 1st, 2nd and 3rd gear while 4th and 5th use the same curve.

This is accomplished with three wires, one of which is grounded by the transmission switch in first, second and third gear respectively.  None are gounded in fourth and fifth gear, this using the same curve for both.

There are four wires coming from the transmission switch, the fouth wire grounds the neutral lamp, turning it on when in neutral.

[rider123]

Oops!! You're right retarding. I see it in my head(timing before TDC) but I'm getting it backwards. I must be "retarded"!

At least we know for sure the TPS is doing something. But my bike still runs better with higher octane. I must have slightly better compression or being brand new my bike just needs it. My old GS750EF liked mid-grade gas as well and it had the same comression ratio as the Bandit. Well hopefully this info will help someone else, just passing on the help to the other guys.