TOPIC:

Hi all,
Basically since I aqquired my GPz1100 back a few yeas ago i've been experiencing what seemed to be a lean air/fuel condition. I systematically checked all "mechanical" type issues, and everything seemed to be in good working order. As I started getting feedback, and an understanding about the "crude" DFI design and the current usage of EPA friendly oxygeynated E10 fuel, I began to realize that i'm thinking I simply have a "too lean" fuel map. My bike always had a lean stumble around 3000-3500 rpms. Unfortunately there's not a lot of info or hardcore experiences about modifying the stock GPz1100's ECU. However a member of another forum who previously owned a early Kawi Voyager DFI (same inherant lean condition) schooled me on a neat trick dubbed the "680 Ohm resistor mod". What some genius figured out was to splice a resistor into the air temperature sensor circut to "fool" the ECU into thinking the air temps were slightly colder that it actually was, which in turn would slightly richen the air/fuel mixture. I tried a 680 Ohm, and quickly realized this made my GPz run a bit too rich. I opted to try a 1K Ohm resistor, and now I made positive progress, my bike really runs awesome ! Gone is the low to midrange hesitations, and seems to pull hard right up to redline. I am going to maybe try a few more resistors, or possibly fabricate an adjustable "potentiometer" type device to adjust "on the fly" over the winter. I'll keep updating this for other GPz1100 members as an FYI. Here's a few pics of this simple and effective mod:

Heres a pic of the 2 wire connector for the air temp sensor (it's to the left of the fuel filter):

Heres the resistor harness wires:

And here's everything all spliced in (no hacking required, as I used male and female spade connectors to plug into the OEM connectors)

that's neat, putting a pot on there would look really cool too

Now that is a great mod! I had grown to accept the 3500-4000 rpm stumble in my brand new 1982 GPz1100 back in 1982...fast forward 25 years in my recently acquired 1982 GPz1100 and its inherent stumble at that rpm

Mcdroid wrote:

Now that is a great mod! I had grown to accept the 3500-4000 rpm stumble in my brand new 1982 GPz1100 back in 1982...fast forward 25 years in my recently acquired 1982 GPz1100 and its inherent stumble at that rpm

You can get the resistors right at your local Radio Shack, so give it a try on your "B2" . Best thing is if you dont like the results, just yank the resistor back out ! No permenant damage or hacking done ! You start opting for "modified" ECU's and mechanical fuel pressure regulators in an effort to richen, now you are getting into more "permanant" type modifications (and expensive). A 4 pak of Radio Shack 1K Ohm resistors is $.99

Polar_Bus wrote:

H...splice a resistor into the air temperature sensor circut to "fool" the ECU into thinking the air temps were slightly colder that it actually was, which in turn would slightly richen the air/fuel mixture. I tried a 680 Ohm, and quickly realized this made my GPz run a bit too rich. I opted to try a 1K Ohm resistor, and now I made positive progress, my bike really runs awesome ! Gone is the low to midrange hesitations, and seems to pull hard right up to redline....

If adding 680 ohms resistance made it too rich, seems like adding 1000 ohms resistance would make it even richer?

Good Fortune!

Patton wrote:

Polar_Bus wrote:

H...splice a resistor into the air temperature sensor circut to "fool" the ECU into thinking the air temps were slightly colder that it actually was, which in turn would slightly richen the air/fuel mixture. I tried a 680 Ohm, and quickly realized this made my GPz run a bit too rich. I opted to try a 1K Ohm resistor, and now I made positive progress, my bike really runs awesome ! Gone is the low to midrange hesitations, and seems to pull hard right up to redline....

If adding 680 ohms resistance made it too rich, seems like adding 1000 ohms resistance would make it even richer?

Good Fortune!

The air temp sensor alters output voltage ranging from 1.7-3.8V . The warmer the ambient air temps are The lower the output voltage, and vice-versa. So my goal is to effectively slightly raise output voltage. To my understanding this is done by increasing the rated ohm output of the resistor ? Geez, I hope i'm doing this right !? LOL

No eBay APP ID and/or Cert ID defined in Kunena configurationThere is a system sold for that. That is tuned for every individual model bike. I bought one for my bike about a year ago. I paid about $7 for mine. I figured out later that installing a adjustable fuel pressure regulator was a better way to go.

Old trick from the mid 80's finds new life in the next century

You have two choices to fatten up the fuel curve on a stock Kawasaki DFI from those days.

1 - Air temp sensor Resistor
2 - Adjustable Fuel Pressure Regulator

For a mild street motor the air temp sensor works very well.

For anything that would require main jet increase on carbs, the FPR is the ticket.

Also, if you drill out the TPS plugs so you can adjust the TPS for highest smooth idle, it can help a bunch with bottom end throttle response. It's simple and very effective.

To do it, slightly loosen the 2 TPS screws and adjust to point where bike idles the highest. Lock them down and adjust your main idle screw on the TB rack for 1100RPM idle.

If you really want to wake it up, send the throttle bodies to Sid Pogue at Pogue Machine in Oklahoma City. Well worth having done

larrycavan wrote:

Old trick from the mid 80's finds new life in the next century

You have two choices to fatten up the fuel curve on a stock Kawasaki DFI from those days.

1 - Air temp sensor Resistor
2 - Adjustable Fuel Pressure Regulator

For a mild street motor the air temp sensor works very well.

For anything that would require main jet increase on carbs, the FPR is the ticket.

Also, if you drill out the TPS plugs so you can adjust the TPS for highest smooth idle, it can help a bunch with bottom end throttle response. It's simple and very effective.

To do it, slightly loosen the 2 TPS screws and adjust to point where bike idles the highest. Lock them down and adjust your main idle screw on the TB rack for 1100RPM idle.

If you really want to wake it up, send the throttle bodies to Sid Pogue at Pogue Machine in Oklahoma City. Well worth having done

GREAT FYI ! Thanks!

I recently bought a GPZ 1100 1984 and am experiencing problems with the stumbling at 2500 to 3500 rpm. I was wondering if you guys ever found a solution for this problem. The problem was more noticeable after I installed the Kerker K2 exhaust 4 into 1. I tried relocating the air temperature sensor closer to the air filter with no results.
If an adjustable fuel pressure regulator is the solution, could someone describe or show how it's done and what make and brand regulator to buy?

www.facebook.com/media/set/?set=a.103702...9715687&l=a44f0b13bc

Thanks,
Steve

Fuel Pumps & Regulators
www.fuel-pumps.net/gsl393.html
www.mpsracing.com/products/MPS/FuelPumps.asp

first off I would try the resetting TPS setting this was lean from factory !this cost "$0" and does work. now if you need more enrichment get adj FP regulator from Pogue its a direct bolt on and and can be returned to orig if so desired but why ???? these 2 can be done to correct 90% of problems. the res mod while it works somewhat you cover up the lean low rpms but you are tricking the ECM to think its colder outside temp but at wide open throttle the engine still thinks in colder temps and therefore not the proper A/F ratio. in other words you are changing A/R across the entire rpm range where as with TPS and FP regulator you can fuel it better across the range.