"Black Sheep" 81 GS550L EFI conversion

[GrantMonast]

Hello, my name is Grant Monast. im from orlando Florida and i am re-rebuilding my 1981 GS550L.
i bought the bike in 2012 from from my friends dad for $400. he was the original owner and there were only around 6000 miles on the bike but it had been sitting for almost a decade.

with much help from this forum i was able to clean and rebuild the carbs, refurbish the tank, fix the stuck calipers and get it into running condition.
i rode it daily to work and university for about 2 years until the stator gave out on me. for whatever reason at the time i stashed the bike in the shed at my parents house and left it there since i had my jeep to drive.

well here we are halfway through 2019 i decided to pull the 550 out of the shed for a proper rebuild a second time. the sticker on the tag indicates that i last registered it in 2015

while any sane individual would get the necessary parts to return it to running condition. when i rebuilt the carbs i wasnt the first person in there. stripped bowl screws and broken float posts were a tell tale sign of novice repairs previous.
i got it running but only just good enough, sometimes sticky float would leak gas everywhere.

i found a decent rebuildable set of carbs on ebay for $99. i didnt buy them.

instead i got a set of throttle bodies from a honda cbr600 and customized them to fit the GS.

i also got a megasquirt engine control module.

some of this EFI conversion was started in 2015 but the project was shelved due to lack of funds and i am returning to the project with a better understanding of the whole system.

i dont think this has ever been done before so this is going to take some experimentation.
even though i was a member in the past i am reluctant to post this here on the forum, everyone will say " just fix your carbs" ,"get a jet kit", "you're wasting your time/money"

are these all valid and truthful points? yes.

am i a foolish, self proclaimed engineer with an appetite for punishment? also yes.

anyway heres what im working with, fresh out the shed, complete with halfway done stator job. custom handlebars, rearhoop, and bread loaf seat all done by yours truly about 5 years ago. windshield came with the bike

IMG_0704 by Grant Monast, on Flickr

IMG_0705 by Grant Monast, on Flickr

 

[Guest]

Nothing wrong with trying new things. Your EFI sounds interesting. I've never heard of megasquirt. Is it a stand alone unit? I had an instructor at MMI that said he had a CBX that he converted to EFI using a Toyota system, but I never saw it, so he may have been full of BS. Show lots of pics, I have a 650L scrambler project that it would be cool to try on.

 

[Grimly]

Just fix your carbs.

Nah, just kidding. Give the EFI a go. The Megasquirt modules are well regarded all over the world by petrolheads everywhere, and for sure there's somebody out there who's used one on a middleweight Suzuki. There have been a few EFI conversions to larger GSs on here over the years, but I'm not sure if those members are still current, that you might pick their brains for useful info.
The biggest piece of awkwardness is the triggering arrangment (I'm just passing on an observation from what I've seen), since the crank nose is already occupied by the ignition triggers. Whether you can make something to live in harmony with that or even piggy-back the ignition timing impulses into the Megasquirt control unit with suitable delay (delay, as in it reads the coil trigger pulse and with knowledge of the engine speed incorporates a predictable delay for the next injection event - or even say, it knows pulse one triggers coil/cylinder one spark, so the same trigger event might be used to pulse fuel into cylinder three, as it's next to go).

It can be worked out - plenty of people have. When it gets down to it, a double-pulse as we have might just be all that's needed to double-pulse the injectors and the fuel/air mix in the throttle body/intake is just sitting there waiting to be intook for burning. So there might not be any need for a delay at all.

 

[Nessism]

A number of people have come and gone through the GSR over the years proclaiming their desire to fit EFI to their GS...and to my knowledge none of them have succeeded or at least none have posted here to that effect. Go for it, pretty sure you would be the first to actually pull it off.

 

[Steve]

Sure, carbs can be cleaned, fixed, etc., but EFI sounds more interesting. I think more people would find it to be more practical on a larger bike, but once you blaze the trail, it might not take as much experimentation to find a larger system that will work.

As Nessism said, several have tried, but we haven't heard of any that actually succeeded, so please let us know. Also, don't be afraid to post some of the stuff that you have tried and found it doesn't work. Someone might be following along and would be happy to avoid that mistake.

I have heard that in 'normal' engines (not Ferrari, Lotus, etc.), fuel timing is not all that critical. There is so little time in between intake strokes, you could almost spray constantly. At 4000 RPM, there are 2000 intake events per cylinder per minute. that is 33 per second, or 30 milliseconds apart. I don't know how long the injectors actually squirt for each event, but it probably won't make much difference where they fire in the crank rotation. You could probably fire them all at the same time and get away with it.

.

 

[dorkburger]

https://www.thegsresources.com/_for...ore-and-fuel-injection&highlight=Efi+big+bore

 

[GrantMonast]

thank you all for the encouragement. a lot of setting up the system is very engine specific which is why i tapped into this forum with such a wealth of knowledge.

i checked the link to the other efi thread, wow very involved!
i am not looking to control my spark, just injector pulses.hopefully i wont need to add any extra toothed wheels or sensors

my first time around on this i had the bike mostly wired but the ignition triggering stumped me. no signal. tried tapping into the coils, and the stock signal generator. nothing.
i did more research and found out i needed a VR Conditioner circuit in order to use the signal for rpm input.
the stock signal generator creates an AC current with sine waves. the conditioner converts it into a square wave DC signal that my megasquirt can read

Here is the VR Conditioner, i dont know much about it or the speeduino system.

Untitled by Grant Monast, on Flickr


Untitled by Grant Monast, on Flickr

 

[GrantMonast]

MOAR Pictures for anyone interested.

Honda CBR600RR throttle bodies widened to match the intakes on my GS
DSC00006 by Grant Monast, on Flickr
DSC00005 by Grant Monast, on Flickr

Temp sensors, notice the one on the left is for coolant temp. whats that you say? i dont have any coolant?! what ever will i do

DSC00008 by Grant Monast, on Flickr

 

[Griffin]

Assuming you are successful in getting it running again, I have three words of advice:

GET NEW TIRES!!!!!!!

Those look to be the original tires still on the bike. Ten years ago I picked up a 550L with similar mileage and identical tires on it. The seller (giver, actually) was the original owner, and confirmed they were the factory skins.

You might as well be riding on the rims in regards to traction.

 

[Grimly]

MOAR Pictures for anyone interested.

Honda CBR600RR throttle bodies widened to match the intakes on my GS
DSC00006 by Grant Monast, on Flickr
DSC00005 by Grant Monast, on Flickr

Temp sensors, notice the one on the left is for coolant temp. whats that you say? i dont have any coolant?! what ever will i do

DSC00008 by Grant Monast, on Flickr

You do have coolant, and it's easily tapped into - I'm assuming the GS550 lump is the same as its larger brethern and there's an oil passage at the rear of the block, where lurks a blanking plug. I'm using that on mine for an oil temp gauge sensor.

 

[Steve]

Assuming you are successful in getting it running again, I have three words of advice:

GET NEW TIRES!!!!!!!

Those look to be the original tires still on the bike. Ten years ago I picked up a 550L with similar mileage and identical tires on it. The seller (giver, actually) was the original owner, and confirmed they were the factory skins.

Absolutely no argument about the need for tires, but did any Suzukis ever come with Raised White Letter tires? :-k

.

 

[Grimly]

I have heard that in 'normal' engines (not Ferrari, Lotus, etc.), fuel timing is not all that critical. There is so little time in between intake strokes, you could almost spray constantly. At 4000 RPM, there are 2000 intake events per cylinder per minute. that is 33 per second, or 30 milliseconds apart. I don't know how long the injectors actually squirt for each event, but it probably won't make much difference where they fire in the crank rotation. You could probably fire them all at the same time and get away with it.

.

I recently came across a comparison of timed sequential (accurate) fuel injection and a couple of different types of batch injection. There's surprisingly little difference in power output. There is enough to be worth doing if you're chasing the most power, of course, but for most uses it's not necessary to go above batch injection. That got my interest up, as doing what the OP is suddenly becomes feasible and attainable at not a huge cost.
With my existing manifold, I can even go Single Point FI, as that's exactly what Rover did when they stopped using the SU carbs, so the SPI hardware is available for me to use should I care to go that road to keep it real simple.

 

[roeme]

Imma sure to follow along. An EFI conversion just for the hell of it on one of mine definitively is in the books for me as well; but resources current and past (no shop, no spare time, ...) prevented me from doing so.

 

[Griffin]

Absolutely no argument about the need for tires, but did any Suzukis ever come with Raised White Letter tires? :-k

.

L models did. Tim's GS 850GL still had the original tires on it the first time he showed up at a rally, with raised white letter Dunlop Qualifiers on it. Just looked at the picture today.

A lot of the "Custom", "Special", and "Limited" models from all four manufacturers came with raised white letter tires.

I guess people thought them to be real head turners back in the day.

 

[Steve]

OK. I have put them on a few bikes myself, just didn't know if they came from the factory that way.

I guess the Ls were 'special' enough to justify the extra cost. :-\\\

.

 

[Guest]

I have recently put fuel injection on a 1970's naturally aspirated Kent 1600 engine using Yamaha R6 throttle bodies, the Speeduino module that you show is used to filter/smooth out the trigger circuit, trigger circuits are used on engines to know where the engine is, you usually use a trigger wheel with either a VR sensor or Hall effect sensor to pick up the missing tooth and know where the engine is, Speeduino helps filter out a bit of the noise that can be generated in home installations. Whether you decide to trigger fuel or ignition or both you will need an ECU to control all of these functions, I used Megasquirt for my car, it is very programmable and people run them on bikes. I would say if you enjoy a project then go for it, I did it for performance with a stage 2 build on my engine with your 550 it is not going to deliver magic performance, it will give more reliable running less susceptible to degrading performance but it will cost you more than getting those carburetors serviced, if you are doing fueling then you might as well do ignition as well because you have invested in an ECU that should do both, . Google "Megasquirt" "HomeBrew" to do some more research.

 

[GrantMonast]

I absolutely am going to replace these tires, I checked the DOT numbers on the sidewall. The front tire was manufactured in 1980 so that?s original. The rear tire has a date code of 1994 probably replaced with factory matching Dunlop

i have the Megasquirt v2.2. It was one of theirs first iterations I?ve had it for over 5 years. It is designed to be used for fuel only installs which is all I want. I plan to use the stock VR trigger for rpm input.

Im not trying to make a performance increase just reliability in all temps. This no way practical but I have been wanting to complete this project as a test of my engineering skills. That?s what I went to school for after all.

 

[GrantMonast]

Here is the wiring diagram provided by diyautotune.

 

[GrantMonast]

You do have coolant, and it's easily tapped into - I'm assuming the GS550 lump is the same as its larger brethern and there's an oil passage at the rear of the block, where lurks a blanking plug. I'm using that on mine for an oil temp gauge sensor.

I will have to check for that. I can either use the cylinder head temp or oil temp. That is up to me to decide which will be more appropriate.
The temp sensor is mainly used for fuel enrichment on a cold engine and leans out when it hits a predetermined temperature.

The fins on the head may heat up faster than the oil. Both will work just have to experiment and test different cutoff temps

 

[Grimly]

I will have to check for that. I can either use the cylinder head temp or oil temp. That is up to me to decide which will be more appropriate.
The temp sensor is mainly used for fuel enrichment on a cold engine and leans out when it hits a predetermined temperature.

The fins on the head may heat up faster than the oil. Both will work just have to experiment and test different cutoff temps

Yes, that would be the problem. I find the oil gauge moves within a couple of minutes of startup, but it takes at least ten minutes of riding before it's anywhere near the normal range of hot enough to be useful for this. Probably not what you need. Cyl head temps obviously much more immediate, but the sensors might be more vulnerable and shonky. A decent industrial or aerospace temp probe designed to last is what's needed. I've seen various ones designed to go under spark plugs or cyl head bolts and I've not been impressed, to be honest. They look shonky and I don't think they last very well.