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Thread: GS1000G mods- big bore and fuel injection

  1. #1
    GS1000G Shopper Guest

    Default GS1000G mods- big bore and fuel injection

    There is an 8V 1100cc big bore kit from an eBay seller in Japan for $168 shipped. I'm using an 1100G cylinder and head.

    The threads here about fuel injection (FI) were incomplete or old.

    There is a LOT OF WORK & expense involved in doing this. My goal is to make it a repeatable project so others can do so if they think they have the time, money, and ability. Not being a super-wrench and hindsight being 20/20, this thread will include the mistakes I made, and the solutions to them. Constructive comments/suggestions are welcome.

    Current status (12/2015): Running, but I ran out of money! Needs final road tuning.

    Table of Contents Part 1
    Due to the length of this thread, below is a clickable list to go to the relevant thing. Part 2 is linked below.

    I'll also try to link/list WHERE to get some of this stuff as well as HOW to do it. If you can't get it (unobtanium) it doesn't matter how it will go together.

    Wiring post link (updated to include connectors for GSXR600 harness)

    Big bore section-

    Fuel injection section-
    Throttle bodies
    • Selection: 2001-2003 GSXR600
    • More info Pics 1 Pics 2
    • Center linkage mod courtesy of member coombehouse (this is the best setup and only required a minor mod by adding a 3/8" block to the linkage), also ST1300 idle adjustment cable
    • Spacing, hardware and fuel rail
    • Airbox I was able to retain the factory box, and used some 45mm silicone hose with smooth bore clamps at the TB ends. The 45mm hose is available in 3" lengths on eBay for <$5 each, you'll need 4 of them or a longer section you can cut up. It's a press fit through the airbox openings.
    • Pods- Use Unifilter UP-4182 if you don't use the airbox. About $15 each on Amazon. More room to mount the fuel pump, but they also have drawbacks such as plumbing in the breather.
    • Fuel rail tested to hold 60+ PSI of pressure. Normal pressure is 43.

    - Microsquirt V3 (found on eBay with 30" harness for about $325)
    • Sensors (purchased at unless otherwise noted, put the below part # in their search window and it will take you to the part):
    • Coolant temp (thermistor) Spectrum Sensors GC4914A-3-100, good for -25C to 300C (-13 to 572 degrees F), specs listed below. This is about the diameter of a 12 gauge wire and can be mounted in a ring terminal with JB Weld and bolted to the head, or a small chunk of aluminum can be inserted between the fins on the back side of the head and drilled/tapped for a 5mm bolt.
    • Inlet air temperature sensor. I used Vishay PN NTCLE400E3222H, good up to 85 degrees Celsius (185 F). It mounts in a single barb nylon fuel filter adapter that was cut off and filled with JB Weld. This part fits into a small rubber grommet in a 1/2" hole in the airbox on the lower right side.
    • Post with temp sensor pics
    • MAP, GM 1-bar, very universal sensor, <$10 on eBay. GM MAP sensor ID/info page.
    • Throttle position (use GSXR600 sensor & calibrate in Tuner Studio)
    • Fuel pressure sensor (optional for PWM fuel pressure control, otherwise use adjustable regulator), AEM 0-100 PSI #30-2131-100, $66. Avoid the knockoff that is on eBay for $25, it would not give reliable readings. Jegs sells the AEM part with free shipping.
    • Fuel pressure gauge, 1/8 pipe inlet, 0-60 PSI preferred.
    • Wideband O2 sensor and controller, Bosch LSU 4.9 or PN 17025 (Amazon link) with Spartan2 wideband controller (BPSX unit originally used had problems and is no longer made). This controller will ONLY work with the Bosch 4.9 sensor. The 4.2 and 4.9 connectors are different sizes. The vendor states the Spartan2 was designed with the Megasquirt in mind and they offer a spreadsheet with Tuner Studio input data.
    • Ignition input- After a lot of trial and error, I am using a 24-2 wheel supplied by GSR member ArttuH. Details are on this post for a 24-2 wheel with new VR sensor and mounting plate. I could not get a reliable signal off the coil. I tried the stock pickups, which use 3 wires, and cut the wires. I added in a 4 wire shielded cable to go back to the MS and tried the "dual spark" setup without success. I ended up making a 24-2 and 12-1 trigger wheel, but neither gave a useable signal with the OEM pickups. Member ArttuH's 24-2 wheel is also pictured here. I have designed a plate with timing marks and a more common 36-1 wheel here. That post also has crank sensor info. The plate & wheel are not cheap (over $250 total) if only 1 each are made. Arttu can sell his 24-2 setup for far less if he has any.
    • Coil driver- The Microsquirt V3 cannot directly drive coils, so you either buy an ignition module such as the Bosch 0227 100 200 (about $40~50 used on eBay, it fits a 1979-2004 Porsche 911 among others) or make your own. See the diagrams page below for a schematic, and this post for how I converted the old GS ignitor box to house these components.
    • Possible Bosch coil driver modules
    • Mounting a coil from a Dodge Neon
    • Wiring diagrams

    Table of contents exceeded maximum post length. I have continued it here.
    Last edited by GS1000G Shopper; 11-12-2016 at 08:17 AM. Reason: Updated status

  2. #2
    Join Date
    Sep 2007
    Mason, OH (SW)


    Oh, crap. The way you research and publish a project, it'll be too easy for me to follow in your footsteps. I'll have to do an EFI conversion.

    Seriously though, I'm looking forward to seeing what you come up with. Are you planning any head work and suspension mods to match?
    O LORD, be gracious to me; heal me, for I have sinned against you! - David

    Skeptical scrutiny is the means, in both science and religion, by which deep insights can be winnowed from deep nonsense. - Carl Sagan

    '80 GS850 GLT
    '80 GS1000 GT
    '01 ZRX1200R

    How to get a "What's New" feed without the Vortex, and without permanently quitting the Vortex

  3. #3
    GS1000G Shopper Guest

    Default Table of Contents Part 2

    Table of Contents Part 2


    Fuel system
    • Bosch #69469 (same as 0580.464.085 pump, <4.5 amps, 12mm or .472" in/8mm or .314" out) from a 1985 VW Transporter. SHOP for it! I found it on Amazon for $89 shipped. It was $120 on eBay. The pump mounts on the front of the airbox. This pump failed before I got the bike operational. I then used a $79 OFP-803 from eBay vendor Only Fuel Pumps (link dead as of 2015, try Rock Auto using the 1985 VW application above). It was shown as a direct replacement for the Bosch pump.
    • A heatsink for a 2" diameter vacuum tube is here (PCF-200) for $22 plus shipping. This will likely make the fit too tight. I did not use one. I used a 52mm silicone sleeve cut in two and a custom aluminum angle bracket with hose clamps. I isolated the bracket from the airbox with rubber grommets and bonded (rubber/metal) washers from Lowes.
    • Pre-pump filter: VW Transporter pre-filter (unk. micron, 7mm in/12mm out) Wix #33274 $4 at Rock Auto; GS petcock to fuel pump
    • Post-pump filter: Wix #33302, comes with 45 degree quick disconnect to 5/16 barb outlet fitting, 5/16 hose barb inlet, QD outlet, has bracket, about $12 each plus shipping; fuel pump to fuel rail
    • Post with pre-pump and post-pump filter pic
    • Two feet of 1/2" ID fuel hose (filter to pump), I found it on eBay for about $4/foot, also 2 clamps to fit
    • Two feet of 5/16" fuel injection hose and 2 FI clamps (if using above filter; otherwise 4 clamps)
    • Dorman 800-120 5/16" quick disconnect adapter. Available at local auto parts stores.
    • Fuel system diagram (revised July 2015 to incorporate AN fitting for gauge and pressure sensor)
    • Pump control- Aftermarket adjustable microcontroller (Arudino did not work, I think they are not suited for this application) Pulse Width Modulation (PWM) returnless system using original GS petcock; retains reserve function, about $50. See post for added parts needed such as enclosure, grommets, and zip ties.

    GSXR600 controls
    (lose self-canceling, gain flash to pass, headlight cutoff when starting, and hazard flashers)
    • Wiring diagram
    • Custom length throttle cable(s) I at first used a custom one that was $25 from eBay vendor steelescycles. You need 90 degree fittings on each end to fit GSXR housings and throttle bodies. The overall length should be 48.5~49.5" with 4.5" of this cable past the housing, so the housings are 44~45". It's better to have this too long than too short. I ended up using the center linkage and found the stock cable would work since everything is in about the same place as stock. The OEM choke cable fastens to the GSXR fast idle linkage.

    Last edited by GS1000G Shopper; 07-23-2015 at 02:25 PM.

  4. #4
    Join Date
    Jul 2010
    Republic, WA

    Default Fuel injection

    Try this as a starting place for your fuel injection.
    1982 GS750EZ
    1978 GS750EC

  5. #5
    Roger P. Guest


    I thought this idea for converting CV carbs to throttle bodies was a neat solution.

    He used off the shelf Mustang injectors then made adapters to slide them into the existing carb bodies to utilize the existing butterfly valves

    My apologies if I have posted this before.

  6. #6
    Join Date
    Jul 2005


    Microsquirt should be a good choice.

    For coolant temp sensor you basically want to measure the cylinder head temp, preferably from the intake side. I have used a NTC thermistor glued on a ring wire terminal. Then you can bolt that on suitable place. A handy and good enough location is the cam chain tensioner bolt. Another possibility is a valve cover bolt but there temp may drop too low in cool weather.

    As far as I know the GPZ TBs are the only ones that fit in without re-spacing. But like you said they are getting old and rare. 2001-2003 GSX-R600 TBs are quite good choice if you want something more modern. They are quite easy to re-space and the cylinder head spigots aren't overly large.

    Fitting some kind injector adapters on original carbs is always an option too. But I'm not sure if it will be any easier than fitting some throttle bodies in the end.

    For fuel pump almost any EFI pump will do but you need to watch carefully the current consumption of the pump. There isn't much extra current available from the generator and the pump is the main consumer in the EFI system. That's the reason why old GPZ pump would be interesting option. The GPZ pump draws only about 3.5A while some car pump may draw 6-8A.

    Fuel return can be routed to the tank through original fuel tap hole. Just make an adapter plate that has connections for take-off and return. It's a good idea to add some extended pipe inside the tank for return but it doesn't need to end over the fuel level. So something like this:

  7. #7
    salty_monk's Avatar
    salty_monk is offline Forum LongTimer GSResource Superstar
    Past Site Supporter
    Join Date
    Oct 2006
    London, UK to Redondo Beach, California


    One bike I have seen ran the stock submersible fuel pump inside a 1/2 gallon or so Aluminum tank which was then gravity fed from the original tank.
    Benefit (other than being able to use the original pump) was that the small tank acts as a "swirl pot" (i.e. stops the fuel pump from running dry of fuel with the bike leaned over or with acceleration /braking surge).

    The adapter idea for the CV carbs was poo pooed for several reasons (most of which seemed valid) elsewhere on the forum.

    1980 GS1000G - Sold
    1978 GS1000E - Finished!
    1980 GS550E - Fixed & given to a friend
    1983 GS750ES Special - Sold
    2009 KLR 650 - Sold - gone to TX!
    1982 GS1100G - Rebuilt and finished. - Sold


  8. #8
    Join Date
    Jul 2005


    Yep, I guess those thermistors will work just fine. If the resistance is in suitable range, about 1-10 kilo-Ohms @ 25C. Alternatively you can get them from any electronics shop. Something like this.

    There are two versions of the GPZ TBs. Earlier version doesn't have injectors but the later has. The GSX-R injectors flow about 280cc/min which is enough for almost 200hp. So they should be just fine for your bike. Generally injector size requirements depend on engine power not size.

    Finding a good external pump with small current consumption isn't too easy. I guess that there are some suitable pumps on modern FI bikes but I can't name any candidate for sure. At some point I had a Mallory 4060FI pump which was quite good. It draws only about 4.5A and produces enough flow for about 300hp. Downside was relatively short maintenance interval.

    One option is to use some "too powerful" pump and reduce voltage to drop flow and current consumption. I have made a small voltage regulator for this purpose. It drives the pump at about 50% current in normal conditions and switches it to full power when more fuel is needed (above 7psi boost).

  9. #9
    GS1000G Shopper Guest


    I gathered some data and made some scale drawings of several throttle bodies. Neither the GSXR600 nor the GPZ1100 shows as a direct fit, although the GPZ is closer. I need to examine the intake boots from the GSXR600. It appears the spacing for 1-2 and 3-4 are the same on the GSXR600 as the GS1000, so the only sectioning needed would be between 2 and 3- presuming the larger GSXR boots could be fitted to an 1100G head.

    Megasquirt forum page with lots of TB data

    This site has some spacing specs for various bikes.

    Linked are photos from the diagrams:

    GS1000 vs GPZ1100:

    GS1000 vs GSX400:

    GS1000 vs GSXR600:
    Last edited by GS1000G Shopper; 06-11-2015 at 09:00 PM.

  10. #10
    Join Date
    Jul 2005


    It seems your dimensions for the GPZ TBs aren't correct. At least my set had 78-93-78 mm spacing.

    Yes, outer pairs of the GSX-R TBs will probably fit without modifications. There is a 2mm difference but the boots will probably flex enough to cover that. However, I shaved some material off the bodies to get spacing exactly correct. There are few pics about the process:

    I used original GS1100/1150 boots. They accepted the GSX-R TBs with moderate forcing.

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