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EFI updates

Started by chris900f, January 30, 2023, 07:11:35 PM

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Nice! I bought an arduino UNO and plan to use a microcontroller in the gs soon.

I have a friend who is a Python developer so if you have any doubts don't hesitate to ask.

About the cap on the speed sensor I suppose it's the noise that you are filtering.


Cool, once I get the fuel delivery sorted out I'll hit you up for help encoding the rotor for the ignition :cheers:

When going back and forth between cap/no cap on the input signal. I noticed that without the cap, the input would run high--about 10v and the led on the input signal conditioner was "on" continuously, until the engine was started, when it would begin to flash in sync with the rpm.

With the cap installed, the led on the input signal conditioner flashes once at power-up, and doesn't light up or flash again until the engine starts.

I now think the cap charges, and only discharges on the voltage drop from the tach signal pulse. It seems that without the cap in place, the 10V output from the Tach pin drains continuously through the Speeduino and completes the circuit. The bike's mechanical tach isn't seeing enough voltage, or enough of a voltage drop to register the pulse.

Luckily it was an easy fix, The cap was from a DIY capacitor-discharge ignition kit I bought about 30 years ago and never built. You may have a point about line noise filtering, I think I just need to add a 10k resistor in line with the cap...but I'll have to check on that.


Plugging up the holes. I used black silicon, and a silicon plug for the larger cavity.


The silicon didn't work very in the smaller holes, so I ended up cleaning it out and using JB weld.

I should have just done the whole job this way as the JB is much easier to work with.

My trick for filling small holes with epoxy; mix it right in the syringe

Once the epoxy hardens, just peel the tape for a perfect flush radius.


Some detail shots of the TPS and mounting plate.


At 11,000rpm each injector fires 22,000 times per minute.

Quick math re: end of video, 50ml in 30 seconds or 100ml minute = 6L per hour at 11,000rpm
using a fuel table based on the Honda's 225cc cylinders. But the fuel level dropped  from 10ml
to zero after cutting the pump; possibly indicating that the gravity feed doesn't quite keep up
with the pump under extreme demand.


I'm loving these updates! Really cool project  :)
2006 GS500 Naked Touring Bike


Thanks Roof, here's the latest...

After spilling a lot of stinky solvent during my first tests, I was looking for
a cheap fuel tank on Amazon. I ended up getting this low-cost, low-pressure pump instead.

Some interesting results: at 9500 rpm it took only 3.5 minutes to fill the jars.
The LP pump seems to be overdriving the main pump. After some google searches I found that
this is a common problem for carbed bikes that use a LP pump, like the Honda Magna. The Magna
pump runs 1-2 psi and these cheapo replacements run 4-7 psi. Put one of these in a Magna and it
will run super-rich.

The extra volume isn't a problem, since I can control the pulse-width of the injectors via
software. Luckily though, I tried running the system at idle rpm for an extended period and
discovered an issue at low rpm. After a few minutes of idle speed flow (think sitting in traffic)
the injectors began making a stuttering sound and both pumps began to get hot. I'm guessing t
the over-pressuring and limited flow thru, was causing the fuel in the main pump to cavitate,
actually impeding flow...

Oh well, the Amazon pump was under $20, and will be useful for draining the fuel out of yard
equipment etc.

The flow between the TB's is well balanced. I'm considering an OEM 1-2 psi pump from a Magna or something
just to be sure the modular pump doesn't outrun the gravity feed from the tank.

*note the color of the was pink? I guess the injectors are nice and clean now.


I mentioned earlier in this thread that power (electrical) can be a challenge when
converting a carbed bike to EFI. It was the only real problem I faced with my Honda,
as I run a 5 amp Denso pump in that bike. I eventually solved the issue with LED
lighting, saving about 60 watts worth between the Headlight, taillights and signals.

For the Suzuki, I found an LED replacement headlight bulb that actually fits the F housing.
This change alone frees up about 35 watts, and that may be all I need.

I wanted to know what the pump (or pumps) and CPU consume, but I don't have an ammeter.
I found the answer on Youtube. Using a low-ohm resistor and a regular multi-meter
I was able to get two data points from each device and used an online "ohm's law"
calculator to get amps and watts.

Main Pump: resistor - 1.3ohms
          measured voltage across the resistor - 2.26v
            = 1.73 amps
            = 3.93 watts

Low-pressure pump r - 1.3ohm
                  v - 1.78v
            = 1.36 amps
            = 2.44 watts

ECU         r- 1.3 ohm
              v- .3v
            = .23 amps
            = .3 watts

Full System   r - 1.3ohm
              v - 3.7v
            = 2.85 amps
            = 10.5 watts

I confirmed that each pump will run fine and not blow a 2 amp fuse, and the whole system will run
with a 4 amp fuse (I didn't have a 3amp handy). This is a big relief. The 35 watts conserved by the LED headlight is enough to
cover everything so far, with enough left over for the relay(s) and an O2 sensor. :)



Not really EFI specific, but since I've never liked the amount of pull-back of the stock bars I decided to swap them for these chromeys from a'76-77 Honda CB400 Four.

They are a little lower and quite a bit flatter; they free up a little extra cable length, and with the barback mounts the reach is acceptable. I had bought them new around 2002 (one of the last few sets in Canada), but they felt too low for me on the Honda. They were considered a cool mod for the Supersports, since they are a direct swap. Unfortunately I had to drill them for the Suzuki's placement of the control mount stays.

Although the manual says you need to cut off the left grip, I learned a trick from a buddy. You can work the little red straw under the end of the grip and hit it with the compressed air to make it pop. Once you have enough space under the grip, slide in the straw for the silicone beside it and give it a few squirts then give it a twist and it slips right off.

Instead of gluing it on with adhesive, I'm trying another trick. I cleaned the inside of the grip with alcohol to get rid of the silicone, and then sprayed acetone (I used carb cleaner) inside to act as a lubricant to get the grip on the new bar. The acetone melts a few microns of the rubber surface, and after it dries for a few hours it will stick like glue--seems to be working, I guess I'll see tomorrow.

I had to loosen off the banjo bolt for the brake reservoir and it dripped a bit until I got it tightened down in the new position, so I left everything protected overnight--I've had previous bad experience with brake fluid and paint >:(

The new/old bars feel pretty good, but I won't really know till I ride I guess.

Update: the acetone trick worked perfectly...I'm thinking this is how they do it at the factory, since there didn't seem to be any glue residue on the original bar.


New bars look pretty good

Throttle bodies installed,

but sadly I don't have room for the long intake tubes.


On the bright side. the fuel rail clears the starter cover by a few mm and sits well inside of the clutch cable (which wasn't a given with the re-design). The control cables, including the fast-idle (choke) cable are all connected and working well. The lower bars/barback combo function as planned so there is plenty of slack that even at full turn.

The big 10 micron fuel filter might not make the final cut, which is too bad. When I dumped the filter contents there was a big glob of water in the catch jar. None of the water made it to the output side of the filter though. The open solvent supply tank must have absorbed some moisture over the days of testing. It would be nice to have that kind of protection as a permanent feature, but I did find out that the smaller plastic filter is rated at 12-15 micron...still pretty good.

Next steps: Main fuel pump, low-pressure fuel pump, and filter; then on to Fuel pump/O2 sensor relay...lots of little details and fitment issues to work out before installing sensors and wiring up the piggy-back harness.


EFI fuel pump installed, I plumbed it for gravity feed for the time being...Loops are better than kinks, I still need to put some clamps on the high-pressure hose.

I'm going use the air box mounts to hold some kind of shelf (see magnet stick) to hold relays, fuses and the air temp sensor. If it turns out I need a low pressure pump I can mount it on the under side of the shelf, but the one I have is too big and awkward for this set-up. I rerouted the injector harness and TPS to run though the center of the bike, to keep the stock harness routing from getting too "lumpy" on the sides of the bike.

Right side: you can see the rear fuel pump mount on the battery box. I fabbed it out of a card blank from an old computer. The front of the pump is mounted to the frame rail with a through bolt. The bolt is held down on either side on rubber cushions cut from some old Honda engine manifolds and secured with two hose clamps. It's really solid, and the threaded through-bolt hole on the pump has a conical rubber cushion on either side, held tight with nuts and washers so there is no metal to plastic contact. The cushions are used valve cover bolt seals, again from the Honda.

Left side: As you can see, the clearance over the starter cover it very tight. I got lucky bench-building the fuel rail off-season. The material sandwiched in between the rail and cover is heat resistant silicone with some kind of fiber weave reinforcement, it provides amazing insulation for something so thin.

The plugged hole casting for the previous generations tach-drive, is where the cylinder head temperature sensor will go. It's almost the right size. I need an M10x1 tap and a 9mm bit for that job; I can get them locally, but I might have to wait a bit.

On the header cross tube, you can see the marking for the O2 sensor. I bought a radiused "saddle" style bung, but I'll need to take the pipe to a welder to get it installed.


Wow, you are getting so close. No offense, but I thought this would be one of those projects that fizzle out and never leave the bench. We had seen attempts at GS500 fuel injection before but I don't remember any of them actually finishing.

Hats off to you!


Thanks Blue, keeping fingers crossed and knocking on wood. :) I got hold of the M10x1 plug tap and a 23/64ths (9mm)drill bit today! Lucky I'm in an oil town with all the industrial supply shops.

I then went to a Princess Auto, which is kind of unique to Western Canada, they have all sorts of cheaper tools and supplies for "farmer fabrication" :wink: and found some pre-wired relay kits for adding LED lights to vehicles in the surplus section. I got two kits for the price of a single relay and socket at the regular auto-parts store, and these have the inline fuses, battery leads, switches, and some nice cable sheathing--another lucky find.

I think this guy may have the only running EFI GS500 on the planet. Pretty rough, and he bailed at the tuning stage, but I have to give him credit: He designed/built his own computer and coded his own software from scratch :icon_exclaim:


Went down to the Bike salvage place today. The owner owed me a few hours from last winter, so he gave me a some parts for the project as payment. I took two low pressure pumps and will bring back whichever one doesn't fit.

I made a shelf to fit between the airbox brackets (kind of a rough job, but its a thick, sturdy piece of aluminum flat bar) After some back and forth I managed to fit this under the shelf, clearing everything.

Both spigots face the same direction, so it should be pretty straightforward to  plumb it in with minimal cuts to my gravity-feed set-up.

The paint pencil was mostly rubbed off but I was able to discern/guess '?8, Honda and V65 from what was left. After I cleaned it up a bit, I did a quick test with solvent and it runs great.
The current draw test indicates about 4 watts.

The other pump was a little cleaner, but the spigots faced 90 degrees from each other--so no go. I couldn't use either of the stock mounting brackets, but I was able to use the rubber insulator from the 90 degree pump, so I can attach this one directly to the shelf with yet another hose clamp, (I'll add 2nd to make it more secure.) Currently it's just tacked together with whatever I had on hand to check the fit and make sure the tank clears. All good so far.

The yellow hose is on the output spigot. I need to use the filter as an adapter between the 5/16" hose and the smaller 1/4" that the EFI pump uses on it's input side. I have one brass 5/16" 90 degree fitting left in my inventory, I need one more to make a u-turn back to the the output from the petcock to the input of the Honda pump, then a short piece of 5/16" hose to reconnect to the filter. I think I'll be able to tighten up the loop a little too, so it doesn't sit on the engine-side rail of the injector rail assembly.
One other advantage of using the LP pump is that the petcock should function in all positions--running the EFI pump as gravity feed the petcock only flows in prime--so no reserve.

I almost forgot to mention this little gem, a Denso narrow-band O2 sensor--very nice, looks almost new.

I did a current draw test and it pulls around 12-13 watts at start-up and drops to about 6 watts when fully heated up. I tested the response using a multi-meter. The mechanic's trick is to power it up and wrap it in a piece of heavy cotton cloth, like denim (anything that won't melt). You spray a little WD40 on the cloth first. The sensor will detect the O2 in the evaporating WD40--you measure the voltage between the output and ground, with the two "same-colour" heater wires connected to the battery. The voltage is small, it will quickly rise from 0.1v to about 0.9v if you've got a winner.

Because the current draw is pretty high at start-up while the sensors heater brings the element up to temp (about 500F) It's good to have some way to delay power to the sensor, and let the exhaust gas warm it up first. I'm mounting the sensor in the header cross-tube, so it should heat up pretty quickly.

The Speeduino software has a temperature-driven app for a cooling fan. So you can use the cylinder head or coolant temperature sensor to trigger the fan relay at whatever temperature you choose. The NO2C board I'm using doesn't have a specific output for a fan, but you can select an output in software--I just need to figure it out.

This is why I bought a second relay--(you MUST have one for the fuel pump(s) for safety, so the fuel stops when the engine stops.) This is just a little bit of extra slickness and insurance so you aren't drawing power while starting a cold bike with a weak battery some day, (and you don't have to think about it.) On the Honda, I just use a toggle-switch. If I can't stuff in an extra relay, socket etc. I can always just opt for the  manual switch.

Once the tank and fairings are installed the whole set-up should be pretty stealthy.


Installing the cylinder head temperature sensor: the scariest part of the job so far...

A very tight fit to use the drill, and had to use a mini vise-grip instead of a tap wrench
I only cut about 6 threads, just enough for the sensor. The sensor fit tightly, but there
was a small gap. You have to be careful with the aluminum sensor and overcome the urge to
overtighten to make it look right. Imagine the joy of snapping it off in the head :mad:

Instead I made a second, thin washer out of a 3/8" ring-connector and tightened it down
solid. I used a tiny bit of Permatex hi-temp thread seal.

Quote for the day: "don't let the perfect be the enemy of the good"


I bought this radiused O2 sensor bung on Amazon, but I still had to spend an hour(more) grinding to get a tighter radius for the GS's small diameter headers. This is going into my 1989 pipe (currently on the bike).

To get the right diameter I stuck some sticky back 3M 220 grit to the header of my 2005 pipe and just zoned out--zoop-zoop-zoop...check,rinse & repeat... :icon_lol:

I have a small neodymium magnet under the plug holding it in place to get it centered and get the angle right to miss the cross bar. I found a welder/fabricator guy via the bike wrecker; so I'll take it to him next week. The paint pencil marking will let him do the job without any guesswork.


I had two NPT fittings left over from the TB build, so all I needed was a coupler to make the u-turn back to the low-pressure pump.


Removed the exhaust to take it to the welder and took some pics to shown the difference between
1st gen and last gen. The later exhaust can is about 3" larger in circumference; the increased pipe diameter
seems to be for aesthetic purposes. There is a noticeable difference in weight of about 4 or 5 pounds.

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