82 GPZ +other bikes - Air temp potentiometer mod

I have a 82 GPZ1100, but I think this works on some other models.

So I had to fix mine so I decided to post what it was. There is a bunch of talk on the forum here about the potentiometer mod but no one talks about the specifics so I would figure I would give back to the community and provide some details.

The one that came on my bike is a CLAROSTAT 73JA-1K POTENTIOMETER 10 TURN 1k OHM 2 WATT. There are 3 pots on this potentiometer, my bike only has the two furthest away from the knob hooked up.

I use it almost on a daily basis. It has 3 uses, as it dials in your AF ratio a little. For example when I'm in heavy traffic the bike runs hotter and starts to idle slightly worse, so I give it a few turns and it becomes happy. When its normal temp I can tune out that mid hesitation these bikes are notorious for. Lastly the previous owner put a bunch of hi-way cruising miles on it so he would dial it leaner to get better fuel economy. I'm at 4000+ft so I'm running rich from the factory settings.

Now for the people that have the single fixed resistor I'm not sure I see the benefit. I notice considerable differences after a couple rotations. It's a 10 turn so I probably can notice 4 different variations of tune. A single resistor to me would be quite limited performance is my guess if I can notice 4 differences in mine..

In the end an AM FPR is best but this is a 20-30 dollar investment for some noticeable differences. I think an aeromotive FPR is around 150 without hoses so this is a considerably cheaper investment.

These bikes will run rich if the one way fuel return valve is clogged too. It's on the bottom right side of the tank, connected to the fuel pressure regulator.

Very interesting topic. I just started thinking to do the same thing. :laugh:
Your pot can adjust value from 0 to 1000 ohm and single turn increase 100 ohm, right? Do you have enough resistance though?
I assume that you need 10 times more resistant, 10k ohm pot, to feel the deference. Did you connect the pot in series?
How do you make the mixture leaner? I am curious because, the series connection doesn't allow to decrease the resistance value.

I did math and experiment for air temp sensor mod, and I would like to report to the forum.
The goal is to create manual controllable fuel system without spend too much money.

Math:
At 20°C, if you want to increase the fuel by 7%, you'll need to tell ECU that the temperature is 20°C lower than the current degree which is 0°C by adding 3.5k Ω to air temp sensor.
(at 0°C, air is about 7% denser than at 20°C and you need to pump up fuel to keep same AFR, air/fuel ratio)
At this setting, AFR value decrease around 1 point. If you got 14.7 AFR at the original setting, you will have 13.7 AFR by the adjusted setting. (not so much )
By the same method, you can know that you need to add 10k Ω, if you want 7% more fuel at 0°C and 1.3k is needed at 40°C. You can do the math with the attached excel file.



There is not much information about the GPZ's air temp sensor available, I only can find 0°C=4.7-7.6kΩ, 20°C=2-3kΩ, 30°C=1.4-2.2Ω, but I assumed that characteristic of the GPZ's is not far from generic thermistor character.
I applied thermistor character equation and I found that it is within the range.
That said, if you need a replacement of the air temp sensor, most likely you can find parts and make it by your own with very littler money. I believe that the air temp sensor is out of stock.

Experiment:
I got a 10kΩ potentiometer from Radio shack and assemble for a quick test. For this test, I removed air temp sensor from ECU and connect to the pot directly.
I play around the pot between 4kΩ and 10kΩ range, I felt that at the higher value, you get richer fuel. That means it works!!
For the next experiment, I will need a better pot, linear taper or revers log taper, for better match to this system. The one I got for this experiment from Radio Shack was audio taper and doesn't give me enough range at the higher value and too much range at the lower value. I also need to upgrade my cardboard made mounting plate to something better. :blush:

Tito, did you end up putting your resistor in series or parallel to get the leaning? How did the reverse log pot work for you? How did you mount it for adjustment during riding? under the tank by the petcock or fast idle lever? I am very interested in being able to tune my 1982 GPZ1100