Carb EFI Conversion: VM or CV?

[93Bandit]

I've been reading all the EFI conversion threads I've been able to find here, and haven't found one yet that has the complete process documented with a reliable running bike at the end. I know of a few folks who have completed the project, but I haven't seen documentation of their builds, just comments here and there. Most I've seen involved retrofitting EFI from a more modern bike to the GS.

I also came across a guy who makes CV carb EFI conversion kits.

Someday when I get my bikes finished, I've thought about trying to build an EFI setup for one of my GS's and document it here. I won't be another one of those people who start the build then never finish and members never know what happened. I won't start it unless I have the means to finish.

Anyways, if I follow through, I'd like to use a set of factory carbs to modify for EFI. That being the case, if it's possible, which version would make the most sense? In my very basic understanding of VM and CV operation, I'd think VM would be better suited since it doesn't rely on vacuum/airflow to operate the slide. The VM carbs are more "mechanical" in operation. Plus, I've got a set of VM carbs that are otherwise scrap, so perfect for the experiment.

I was thinking, all the fuel and air passages in the carb bodies could be plugged/blocked so that the carbs are essentially only a throttle body. I have quite worked out where I would introduce fuel, but I'm thinking of a custom intake boot/runner that is longer than OEM and has space for injectors to be tapped into, between the carb throttle bodies and the head.

I would try to keep the carbs as factory appearing as possible which is another reason I'd like to use the carbs for the conversion.

As I mentioned previously, I've got a complete spare 750 engine with junk VM carbs that I would build the EFI system around as proof of concept. Then, if it works, I'd install the system on a running bike for fine tuning. So I wouldn't be ruining a running bike while trying to get it to work. A running bike would only be done once I've proven the system works and can be installed on a bike.

Anyone care to provide input? Would my idea with using VM carbs and plugging them be possible? Any other thoughts? Any input is appreciated.

 

[Steve]

Functionally, I don't think it would matter very much which carbs you used. The main reason for the slides in the BS carbs is to maintain airflow velocity over the jets to prevent the bogging that the VM carbs have when you open the throttle suddenly. If you have fuel injection with a mapping program that will compensate, you could epoxy the slides in the full-up position.

The main difference would come down to appearance and which bike they are going on. If you want to maintain a "stock" appearance, yhou would use VM carbs on '79 and older bikes, and BS carbs on '80 and newer bikes.

Your longer intake runners might not be noticed much by the average person (we GSers are MUCH better than average :encouragement, but what about the injectors you would attach to them? :-k

Do the injectors have to be installed between the throttles and the engine? If not, how big are the injectors? Is there a chance the carb bodies can be drilled out on the bottom, to have the injector spraying UP, where the main jets and needles live?

I obviously have NO experience playing with injectors. I only know that they spray fuel when opened. I don't know if the spray can be directed at an angle or if it has to be inline with the injector body. I don't know if it's narrow enough or short enough to fit into the bottom half of a carb, but I do think the (now empty) float bowl would be a great hiding spot, if it fits.

If you need some BS carbs to play with, I have a few candidates.

.

 

[Buffalo Bill]

Not surprised you couldn't find examples of a successful post conversion. I'm sure there are some, because people have been doing it on old cars since the 90s.
Problem is most new bike engine heads are designed for EFI with short intake runs with steep downhill angles. Very different from a GS with it's horizontal intake.
Building a proper EFI system is only the first part of the conversion project. The long hard part is endless testing and programming a working fuel map.
There needs to be an oxygen sensor located in the best place of the exhaust system.
Starting from point 0, you got a long road ahead before you got a good thing going.

 

[93Bandit]

Functionally, I don't think it would matter very much which carbs you used. The main reason for the slides in the BS carbs is to maintain airflow velocity over the jets to prevent the bogging that the VM carbs have when you open the throttle suddenly. If you have fuel injection with a mapping program that will compensate, you could epoxy the slides in the full-up position.

The main difference would come down to appearance and which bike they are going on. If you want to maintain a "stock" appearance, yhou would use VM carbs on '79 and older bikes, and BS carbs on '80 and newer bikes.

Your longer intake runners might not be noticed much by the average person (we GSers are MUCH better than average :encouragement, but what about the injectors you would attach to them? :-k

Do the injectors have to be installed between the throttles and the engine? If not, how big are the injectors? Is there a chance the carb bodies can be drilled out on the bottom, to have the injector spraying UP, where the main jets and needles live?

I obviously have NO experience playing with injectors. I only know that they spray fuel when opened. I don't know if the spray can be directed at an angle or if it has to be inline with the injector body. I don't know if it's narrow enough or short enough to fit into the bottom half of a carb, but I do think the (now empty) float bowl would be a great hiding spot, if it fits.

If you need some BS carbs to play with, I have a few candidates.

.

All your questions are the same I've asked myself and am pondering. As for stock appearance, hiding the injectors will be difficult. I'm not looking for a 100% stock appearance, I don't mind if some EFI components are visible. I just like the look of the carbs.

As for injector location, I've been wondering if I can place them vertical in the bowl so that they spray up through a port where the needle jet and jet needle are, but I'm not sure if that will be problematic when the slide is all the way down at idle, or if the 90 degree angle to go into the port will disrupt fuel atomization? Lots of unknowns.

Or, what if I built a type of "spider injection" similar to what GM used in the 90s? That way I'd only need 2 injectors and I could run a fuel nozzle to the area the main needle jet is in each carb. This option may allow me to place the injectors in a less visible location.

Another problem with using the carbs instead of throttle bodies is I'll have to rig up a TPS to the throttle shaft.

I have a few ideas, but all will take prototype builds to see if they'll work. I may take you up on that offer for the BS carbs. I may need to experiment on a couple different injector locations/setups to get something that works.

 

[LAB3]

My working knowledge of EFI could be engraved on the head of a pin with a rusty shovel. The best option I can think of is to draw a deep breath, take sip of gas and spray it into the air box.

 

[Steve]

As for injector location, I've been wondering if I can place them vertical in the bowl so that they spray up through a port where the needle jet and jet needle are, but I'm not sure if that will be problematic when the slide is all the way down at idle, or if the 90 degree angle to go into the port will disrupt fuel atomization? Lots of unknowns.

I mentioned earlier that the slides are there to maintain airflow velocity over the jets. With injectors, you do not need to maintain that velocity, as the mapping in the computer will inject the proper amount of fuel, so the slides are unnecessary. You could remove them and find a way to block the hole they sit in, or just raise them all the way and epoxy them in the up position.

If you decide to try this with BS carbs (the CV-type), I have some bodies I can donate for experimentation, as well as some slides with damaged diaphragms. The diaphragms won't be needed for the fuel injection, and it would be nice to save the ones you have.

.

 

[Rijko]

good info, may save some time/grief :

http://www.thegsresources.com/_forum/showthread.php?202848-GS1000G-mods-big-bore-and-fuel-injection

http://suzukigs500efi.blogspot.com/

Maybe you can buy a kit from Scheepers ?

http://www.youtube.com/watch?v=-mwTIadyhcY

 

[93Bandit]

I mentioned earlier that the slides are there to maintain airflow velocity over the jets. With injectors, you do not need to maintain that velocity, as the mapping in the computer will inject the proper amount of fuel, so the slides are unnecessary. You could remove them and find a way to block the hole they sit in, or just raise them all the way and epoxy them in the up position.

If you decide to try this with BS carbs (the CV-type), I have some bodies I can donate for experimentation, as well as some slides with damaged diaphragms. The diaphragms won't be needed for the fuel injection, and it would be nice to save the ones you have.

.

Correct me if I'm wrong, but if I'm using VM carbs, wouldn't I have to keep the slides operational for throttle control? There aren't butterfly valves in VM carbs, only slides. So the slides would act as the butterfly valves, like in a conventional throttle body, correct? I understand the CV carbs could have the throttles fixed in the full-up position, because they have a butterfly valve. Or am I totally wrong?

I would gladly take any carb bodies and slides you have, as long as you don't mind them being "damaged." I think the most "damaging" experimentation will be any drilling modifications necessary for injector, or related component, mounting. I have some ideas but until I can look at a carb body and have an injector in-hand, I'm not sure what I'll need to drill or tap.

 

[93Bandit]

good info, may save some time/grief :

http://www.thegsresources.com/_forum/showthread.php?202848-GS1000G-mods-big-bore-and-fuel-injection

http://suzukigs500efi.blogspot.com/

Maybe you can buy a kit from Scheepers ?

http://www.youtube.com/watch?v=-mwTIadyhcY

I've spent a lot of time reading that first thread. I'm going to attempt to replicate some of the things he did, such as the trigger setup and some of the electronics. Otherwise, I'll be blazing a new trail with respect to the EFI hardware.

I'll have to check out the second link when I get to a computer.

Lastly, what's the fun in purchasing a kit? If it came down to that, I'd just buy an EFI bike. Also, like mentioned in the EFI thread you linked too, I'd like to build and document my project in such a way that it could be repeatable by anyone else who may be interested in converting their GS. I like to help others and it's always been a pet peeve of mine when someone asks a question on a forum, figures it out on their own but never posts the solution. Or just when I find a project thread that's going great and I want to do the same, but it comes to an abrupt end without any further information on progress or if it even worked. I understand it's often due to unpredictable life events, but if I can get a start on this, I'd like to see it to the end and document along the way for everyone's benefit.

 

[Rijko]

i like the idea of EFI on an old GS, especially for a tuned bike.
Hiding the system in carb bodies like Triumph did, i like even better.

i met a guy some years ago, who built a working EFI for a Suzuki GT750.
Documented that pretty well online, too.
But the amount of money, effort and time he had to spend .. like the guy from that 2nd link i posted, is enough for me to not even try.

what's the fun in purchasing a kit ?

Well i have a souped up GS1000. If i could get that an extra handful of horses for an
acceptable amount of money/effort without the risk of blowing it up one or more times in the process, i would.

The current CR carbs work fine, and i will probably stick with those.
If i win the lottery, i will probably go for the Yoshi MJN's - expensive but probably the best improvement for carbs since they were invented.

I get the fun it gives to build something like this yourself.
I am not an engineer, and have limited time and money to invest in such a project.
But i have crazy respect for those that do, so should you decide to start that project i will
subscribe instantly.

 

[93Bandit]

i like the idea of EFI on an old GS, especially for a tuned bike.
Hiding the system in carb bodies like Triumph did, i like even better.

i met a guy some years ago, who built a working EFI for a Suzuki GT750.
Documented that pretty well online, too.
But the amount of money, effort and time he had to spend .. like the guy from that 2nd link i posted, is enough for me to not even try.



Well i have a souped up GS1000. If i could get that an extra handful of horses for an
acceptable amount of money/effort without the risk of blowing it up one or more times in the process, i would.

The current CR carbs work fine, and i will probably stick with those.
If i win the lottery, i will probably go for the Yoshi MJN's - expensive but probably the best improvement for carbs since they were invented.

I get the fun it gives to build something like this yourself.
I am not an engineer, and have limited time and money to invest in such a project.
But i have crazy respect for those that do, so should you decide to start that project i will
subscribe instantly.

I'd really like to start this build, but I've got other projects I need to finish first. Once those are complete, I do plan on making this the next project.

It would be great if I could hide the EFI components within the carbs, but I'm not too sure the carbs have the space, nor do I have the tool's or skills to accomplish that. But again, even if I could do those things, the average Joe who may be following along and want to duplicate my build on his bike may not be able to. So I want to keep it as simple and sleek as possible.

 

[Steve]

Correct me if I'm wrong, but if I'm using VM carbs, wouldn't I have to keep the slides operational for throttle control? There aren't butterfly valves in VM carbs, only slides. So the slides would act as the butterfly valves, like in a conventional throttle body, correct? I understand the CV carbs could have the throttles fixed in the full-up position, because they have a butterfly valve. Or am I totally wrong?

You are mostly right. :-k

You are correct that there are no butterfly valves in the VM carbs. The slides in them ARE the throttles. (This is why they are prone to bogging when opened suddenly, especially at low engine speeds.)

You are not quite so correct in your understanding of the CV-type BS carbs. (The "CV" is a construction type, not a model or manufacturer.) The slides are NOT the throttles, they are basically a variable venturi system. The butterfly valves are the throttle system.

It's possible that operational slides might enhance the system by still maintaining velocity past the injector, but that would take a LOT of experimentation.

.

 

[GSX1100 dreamn]

Hi 93Bandit,
Have you seen my thread here 'katEFI'. A successful EFI functioning conversion ?!
I do list all of the conversion here and any gaps can be found in the Katana Australia forum, and yes you will have to be a member to view.
As mentioned I spent 6 months preparing and 4 days converting.
That was in September this year and I have ridden it every day to work since. No problems/reliable.
I do need to adjust the fuelling at some stage but totally ridable as is, no fouling of plugs smooth power delivery, etc.
Like you I wanted to create a conversion that anyone could easily repeat and I think I have using a donor bike and factory parts.
As I have mentioned all the perifories e.g fuel pump, trigger wheel etc can all be done differently to individules tastes/preforances of componentes.
Cheers Andrew.

 

[Steve]

Click HERE to see the thread on GSR.

.

 

[93Bandit]

Hi 93Bandit,
Have you seen my thread here 'katEFI'. A successful EFI functioning conversion ?!
I do list all of the conversion here and any gaps can be found in the Katana Australia forum, and yes you will have to be a member to view.
As mentioned I spent 6 months preparing and 4 days converting.
That was in September this year and I have ridden it every day to work since. No problems/reliable.
I do need to adjust the fuelling at some stage but totally ridable as is, no fouling of plugs smooth power delivery, etc.
Like you I wanted to create a conversion that anyone could easily repeat and I think I have using a donor bike and factory parts.
As I have mentioned all the perifories e.g fuel pump, trigger wheel etc can all be done differently to individules tastes/preforances of componentes.
Cheers Andrew.

Hey Andrew, I just looked through your thread. Nice build! Fortunately for you, your bike is similar to the doner bike which I'm sure helped a lot. I'll probably end up converting my 850G which is a little different than what you have. Regardless, I'll have to pick your brain about the trigger system. It looks like you extended the trigger cover by combining two covers? Also, can you post some detailed pictures of the mounting bracket for the trigger pickup sensor?

 

[GSX1100 dreamn]

Hi 93 Bandit,

To answer your question. Yes I cut another ignition cover to extend the original to cover the trigger wheel, not pretty but works for now.
As for the mounting bracket I don't have anymore detail pictures but it was a piece of scrap stainless steel I cut to shape and bolted to the base plate and tapped to mount the pickup.
But also I am still running the Kat ignition setup (does nothing) it was a backup if I needed it when first starting up the EFI, ideally I should pull out the Kat pickup and remount the trigger wheel and pickup further in so I can also use original cover.
Your correct I chose the 1250 Bandit as for capacity it was all but the same as my 1260 Kat so fueling was always going to be very close from start and it is. Otherwise you have to spend $$$/time on a dyno to map the ECU for fuel and if you run it ignition. My o2 sensor is my best friend whether for cabys or EFI it just takes the guess work out of what the mixture is.

Just a few thoughts on setup,

I understand you want to 'convert' carbys to house injectors for that standard look but unless you create the injector angle that a throttle body has you will have very poor fuel atomisation thus negating any benefit/improvement you would normally gain with EFI. Ideally you should get an EFI system up and running reliably with throttle bodies and then once you are happy then muck about with these converted carbys then atleast you know any problems are related to these items and not the new EFI setup.

Another problem is electric power generation as in you will use alot (engine cranking/fuel pump/injectors/lights/ignition) generally more than what the original system was ever meant to cope with, this will need to be addressed. Some EFI converts have changed the rotor/stator from later model higher output bikes whereas others have just added another battery to have a bigger reserve. Either way you have to do something or just keep charging the battery when back home.

Engine management/ECU/computer/ECM call it what you want they all have one and you need to decide what you want to run as it can determine what type of sensors you need to use. After market ECU need to be programmed for all mapping conditions for fuel and if you run it ignition too.

Whereas if you run a factory ECU from a bike that is close to capacity to yours, doesn't just have to be Suzuki it can be any brand and 4cyl then you might be able to get away with only fine tuning the factory mapping, but atleast you have a map to start with and generally close enough to run (like mine).

There are a stack of other things to consider but just a couple very basic ideas for now.

Cheers Andrew.

 

[93Bandit]

Hi 93 Bandit,

To answer your question. Yes I cut another ignition cover to extend the original to cover the trigger wheel, not pretty but works for now.
As for the mounting bracket I don't have anymore detail pictures but it was a piece of scrap stainless steel I cut to shape and bolted to the base plate and tapped to mount the pickup.
But also I am still running the Kat ignition setup (does nothing) it was a backup if I needed it when first starting up the EFI, ideally I should pull out the Kat pickup and remount the trigger wheel and pickup further in so I can also use original cover.
Your correct I chose the 1250 Bandit as for capacity it was all but the same as my 1260 Kat so fueling was always going to be very close from start and it is. Otherwise you have to spend $$$/time on a dyno to map the ECU for fuel and if you run it ignition. My o2 sensor is my best friend whether for cabys or EFI it just takes the guess work out of what the mixture is.

Just a few thoughts on setup,

I understand you want to 'convert' carbys to house injectors for that standard look but unless you create the injector angle that a throttle body has you will have very poor fuel atomisation thus negating any benefit/improvement you would normally gain with EFI. Ideally you should get an EFI system up and running reliably with throttle bodies and then once you are happy then muck about with these converted carbys then atleast you know any problems are related to these items and not the new EFI setup.

That would be an ideal way to go about things, but that sounds like twice the expense to me. I shouldn't have any problems budgeting for a project like this, but doing it twice seems kind of counter productive, financially anyways. But I see your point.

As for the injector angle; yes it would be 90 degrees if I mounted the injectors vertically, placing the injector nozzle near the needle jet. As for poor fuel atomization due to the angle, I agree. I'm still trying to work that out, I have a few ideas on how to mount the injectors at an angle to help with that, but I'm not too sure how well it'll work. Also, I don't know how the fuel will react at idle with the slide so low over the injector nozzle port. The biggest issue right now is I don't have any injectors to play with, so I don't know how big they are which makes it difficult to see where they will and won't fit. I don't know what injectors I'll use either.

Another problem is electric power generation as in you will use alot (engine cranking/fuel pump/injectors/lights/ignition) generally more than what the original system was ever meant to cope with, this will need to be addressed. Some EFI converts have changed the rotor/stator from later model higher output bikes whereas others have just added another battery to have a bigger reserve. Either way you have to do something or just keep charging the battery when back home.

This is something I've considered as well. I've read about some people rewinding the stator for more output for accessories. I still don't know what power/current demands the EFI system will require, so until I get an idea of it's demands, I won't be able to work out a way to meet that demand. I wouldn't think it would be too much though? I think the highest current draw would be the fuel pump.

Engine management/ECU/computer/ECM call it what you want they all have one and you need to decide what you want to run as it can determine what type of sensors you need to use. After market ECU need to be programmed for all mapping conditions for fuel and if you run it ignition too.

Whereas if you run a factory ECU from a bike that is close to capacity to yours, doesn't just have to be Suzuki it can be any brand and 4cyl then you might be able to get away with only fine tuning the factory mapping, but atleast you have a map to start with and generally close enough to run (like mine).

I intend on using the DIYAutoTune MicroSquirt ECU. There's plenty of support for their ECU's, and even more people using them. I think I could make it work with some trial and error. That's half the fun anyways, right?

There are a stack of other things to consider but just a couple very basic ideas for now.

Cheers Andrew.

I have another question concerning the kaw trigger wheel you used. How did you determine how to time it? I see your thread mentions 7.5 teeth from top dead center, but it doesn't appear there's a way to adjust the timing on your setup? It looks like you filed a nut with the slot so that it would fit in the trigger wheel in the right position, but wouldn't you need a little adjustment ability to get it perfect? Or is the pickup able to move slightly to account for any timing error?

If possible, can you send me some dimensions of the injectors you're using? Like overall length, nozzle diameter, diameter at its widest point?

Also, what kind of idle air control valve setup does your throttle body setup use? If I convert my carbs to EFI, then I'll have to work out the idle air control portion. Will the throttle slides sit high enough at idle to allow easy cold starts? Obviously there wouldn't be an automatic high idle with that set up. Could I just compensate with a rich mixture?

 

[GSX1100 dreamn]

I find my highest electrical load is sitting at the traffic lights ;engine idling/headlight on/blinker on/ brake light on and you can literally see the voltmeter drop down from the load.

Sorry no readily available injector dimensions they are stuck in the throttle body, but now we revisit my previous post on setup.

You have decided on an ECU so now you need to build around this ECU with sensors that will work with it. Then that will give you the parts you need to buy and then how to mount them based on their specification.

Thats why I used the components on my setup because they suited the Bandit 1250 ECU.

To answer your question on trigger wheel and ISC.
Here is the stock GSX1100 part I modified to mount the trigger wheel.
Item #7

You can see below the slight elongation of the base plate mount which gives me slight movement to line up the 71/2 tooth position.
Timing is done by the ECU so set and forget.

And the picture below shows the ISC, the two lower hoses and the control soleniod on the left.

Hope this helps but remember this setup only suits my Bandit 1250 ECU you need to research the specific components needed to drive your ECU.
Cheers Andrew.

 

[Spyder]

Hmmm, it would seem to me, that for a GS850, one would look for a GSXR750 setup. (easiest would be an '01-'02)

I have a '95 GSXR that I would like to convert to EFI, and the same setup would likely work out great. The fun part being, FINDING a complete setup. OR, doing a LOT of research, and piecing it together off Ebay... Would also be really nice to have coil over plug as well. Hmmm...

 

[GSX1100 dreamn]

Hi Spyder,
If your choosing a factory ECU setup for a carby bike best to get one with similar characteristics and capacity.
e.g your GSXR and use a GSXR EFI. ( high rpm power engines similar power delivery)
for 93Bandit with his GS850 look at low to mid range EFI bikes like the GSX-S750.
For me thats why I chose the Bandit 1250 for my 1260 Kat.
Then you can fine tune the ECU to better suit your exact engine needs.
Of course if you are going to use an aftermarket ECU then it dosen't matter in relation to the above except for INJECTOR FLOW CAPACITY SIZE.
Cheers Andrew.