MSefi.com read only forum (Jan.15,2018)

Hi all,

After doing more research on my cbr250 efi project, I've come up with a few queries...

For now, it seems the best way of converting the bike to efi is to modify the existing carbs to mount the injectors where the CV slides used to fit. I am tending to like this idea because it seems to be the cleanest though it does have some issues. The fuel will be injected before the throttle valve. That isnt ideal for me but if it is the only way it will work then I can live with it. Are there any potential problems with fuel being injected before the throttle valves? After the valves, the fuel will have a very short distance to travel to the intake valves (less than 100mm at a guess). The other issue is the size of the slide valve opening. The CV slides are flat slides so there is less space to fit an injector in the opening than if they were round slides. From the manual and some other sources, it seems most injectors measure 15mm diameter around the tip. This may fit but there won't be much room to play with. Do you know is it possible to get injectors that are physically smaller with the same flow rate?

I have considered trying to use CB400 nc42 or GSX400 throttle bodies on this as it would make things easier if the tps and injectors were already fitted. The intake stubs are very close to the 250 stubs at 30mm diameter but the spacing is the main issue. The 400's have the throttle cables fixed between cylinders 2 &3, whether my cbr has this fitting between cylinders 3 & 4. The spacing between the other cylinders is also more than likely too big. Honda knew how to package the little 250 with very little room to spare! I havent been able to find any proper photos or info on the CB or GSX 400 throttle bodies and I have no idea whether the individual bodies can be seperated or not. And if they can be seperated, is there a possibility to move the throttle cable plate and reduce cylinder spacing? Does anyone have a set of these throttle bodies that would be able to give me more information on them? Photos, experience or manual diagrams would be great!

Thanks guys!

Edit: I believe its GSR400 and not GSX... my bad.

I think you're going to discover there aren't many people here on the Mega/Microsquirt sites that have any familiarity or experience with your CBR250 or the other small displacement bikes you mentioned. They're just not the usual targets for a fuel injection modification. I found this out myself when I was working on my EX-250. You'll probably find that you'll have to invent your own unique solution if you're going to be successful.

I don't know if you've looked into the Kawasaki EX-250 but over there in Europe it's fuel injected and its throttlebody might be just the thing for your project depending on how much machining/modifying skill you have at your disposal. I found mine on Euro Ebay through an English bike-breaker.

The EX-250 throttlebody has 28mm bores which would match your project's needs very nicely. The bore-to-bore center spacing between this throttlebody's two bores is 67mm (2.6378 inches) which breaks down to slightly less than 39mm (1.5354 inches) measured between the outer edges (metal to metal) of the bores. And there's definitely some "dead space" between the bores in the casting that could be reduced by a skilled machinist. Or you could keep them as-cast and make a short manifold that reduces the spacing as needed to mate up with the CBR250 intake boots. Just a suggestion. A well-executed modification and pairing of two of these throttlebodies could be an elegant solution to your throttlebody needs.

http://www.microsquirt.com/viewtopic.ph ... 7&start=50

The injectors that come with the EX-250 throttlebody are about 214cc per minute (as far as my testing could determine) which might be on the large side for your application. But at 19,000 RPM the math starts to get a bit ridiculous. They're high impedance injectors and being very small injectors they seem to have a short opening time (well below .1ms).

Thanks EWflyer! I know not many have done small bike conversions and as far as I know, I am the first to try it with a CBR250. I was really trying to get a feel for the general andvantages/disadvantages of various TB/injector configurations.

After more thought now I am leaning towards adapting existing TBs from bikes even if it does require machining and modification. Its interesting you should mention the EX-250 TBs. I wrote them off before because I assumed they were too big since they are feeding a 125cc pot while my carbs feed a 62cc pot. But from your measurements they are actually smaller than the CBR carbs! I presume the 28mm you measured is the bore at the throttle plate? My carbs are actually 30mm with a 28mm venturi bore. I guess the rev limit difference is probably the cause of this.

The GSR400 TBs seem to make more sense at the moment being 30mm also but I really should measure the distances on the carbs next before going any further. The GSR bodies will likely need a lot of modification and its not going to be easy to find them either as I will likely have to source a set on yahoo Japan. There was 2 sets up during the week for very cheap money but they didnt have the injectors with them. I would prefer to get the lot together. Though in saying that, maybe its better not to get injectors with them and just fit my own size ones. If you say your injectors are 214cc/min, I would expect the GSR injectors to be a similar size.

I have calculated I need to flow around 160cc/min for my engine. This is probably already on the large side though as I assumed 100% VE at 19,000rpm and AFR 12:1 with an injection time of 1 engine revolution. Just to be sure. Im not sure how to calculate if 160cc/min is too large for idle though...

The only issue I see with getting EX-250 TBs is the cost. Since I will have to buy 2 sets the cost is likely to be a good bit more than if I could source a set of GSR400 TBs. The machining/modification costs for both options are probably going to be very similar. Its not going to be easy either way though! Id better measure the stock carbs first anyway and go from there.

You may have more on your hands than you can handle with that CBR250R.

One of the signs pointing in that direction is the carb/throttlebody bore size issue. If you look around at the difference between "sport" and "super sport" bikes you'll notice the extreme differences in the ratio between bore sizing and cylinder displacement. Most super sport 600cc bikes (4 cylinder) use a 38mm bore on their 150cc cylinders while a sport or touring type of 600cc bike will use a much reduced bore-to-cylinder ratio. Example: Kawasaki's super sport ZX6R uses 38mm bores on 150cc cylinders while their sport-level Ninja 650R uses 38mm bores on 325cc cylinders.

The only way to make these crazy-oversized bores work well in a fuel injection system is to have an ECU-controlled secondary throttle plates in the throttlebody. Of course you know that the old-tech-carb version of ECU-controlled secondary throttle plates is the "slides" on the carbs that react (very precisely) to engine vacuum. Without one of these large-throttlebody-bore-to-displacement-ratio "workarounds" you'll end up with really bad off-idle throttle characteristics and a generally hard to control throttle everywhere except at or near WOT. The super sport bore to cylinder ratio allows the engineers to make huge horsepower under high-RPM, WOT conditions (which wins races and sells bikes), but requires some really carefull tuning and "workaround" engineering to produce a streetable bike.

Another bad omen in a one-of project like yours is that you need a real nice pot of cash to work through it.

Well, the stock carbs on these wee beasties are CV, so that part's covered; the challenge becomes finding a home for the injectors. Thomas and I were discussing the work of a fellow who installed the injectors on his V-Max in the slide chambers, but, obviously, this is a V-Max.

When I first started contemplating adding EFI to my FZR250 (the Yamaha version of Thomas' Honda), I asked the question if it would be practical to have the injectors squirting up through the needle jet ports. Actually mounting the injectors underneath is easy; the question is whether having the spray impinge on the underside of the slide would be good, bad, or indifferent. The actual contact area would be rather small, and the velocity through that throat as high as anywhere in the entire intake tract other than through the butterfly itself. It's one of those things that might await some intrepid soul to actually construct and test...

You're talking about this guy's work, right?

http://roadstercycle.com/yamaha_vmax_fu ... cv_car.htm

Looks like a very good solution to the problem; well engineered, proven on the road, etc., but it doesn't preserve the bike's vacuum-controlled slides which I really don't think the CBR250R could go without (unless you somehow reduced the bores to a size that conforms more to the "sport" bore-to-cc ratio rather than the "super-sport" ratio).

On the upside, the Vmax guy provides a breakdown and itemization of the costs involved in going this direction to achieve fuel injection (to help people gain a realistic perspective on the overall price of a project like this. Because even if, as they say, "your price may vary" he's definitely in the ballpark).

You're right, the CBR250R represents some untested territory. There are all sorts of possible solutions.

Before I read your response I was still thinking about the EX-250 throttlebody solution with regard to the bike's probable need for either a CV slide or secondary butterfly and the fact that there are no provisions in the Mega/Micro-squirt for ECU-programmed control of secondary butterflies. But who needs it when you still have engine vacuum that worked fine all these years on the CV carb slides. All you'd have to do is sample the MAP signal and use it to create an output scaled into an electrical signal to the secondary butterfly servo motor. Rudimentary, yes, but it could make the secondary butterflies act just like a slide. Maybe somebody with real electrical engineering skill could even build a circuit that factors in RPM and other variables (RPMdot, TPSdot) to more precisely control the butterflies.

I have been thinking some more on the CV slide/secondary butterfly issue over the weekend. I hadnt seen it as an issue until you mentioned it EWflyer but you have got the cogs turning in my head.

I've thought about the idea of building a circuit to control the butterflies based on vacuum to simulate the effect of CV slides. The thing is the CV slides are controlled by the reduced static pressure created by an increase in air velocity through the opening under the slide and not by MAP. (If they were controlled by MAP, then the slides would be fully open at idle and closed at WOT) I thought about testing the pressure differential needed to raise the slides and graphing pressure vs flow area and all that but then I realised that it is much more simple than that. The airflow through the carb (or throttle body) is solely dependent on engine rpm! If you suddenly open the throttle, the slides will not rise until the velocity through the venturi increases or engine rpm increases. Therefore, to control secondary butterflies to act like CV slides, all that is needed is a frequency to voltage converter. A basic circuit will need tweeking to convert the input frequencies to the correct output voltage but I think it should be possible. The CBR250 has 2 coil packs so I can use one for the rpm input to the ecu and the other for the input to the butterfly controller. The issue is that the voltage needs to go from -12V to +12V for the butterflies. (This is according to a guy on 400greybikes but I cant for the life of me find the thread again! I should really bookmark all useful info) Any frequency to voltage converter is likely to only have a positive voltage output so this will need to be looked into.

Another idea that popped into my head was to use the acceleration enrichments to soften throttle response at small throttle openings. As in remove the secondary butterflies and reduce the enrichment values at small throttle openings so I get less savage throttle response. Looking in the manual at how the megasquirt manages accel enrichments, this may or may not be possible... the enrichments can be based on TPSdot and can vary depending on the speed of throttle opening but whether that will give me the desired result or not will need to be tested I suppose.

Then again, this must have been addressed on other super-sport bikes which have been converted to efi... any carbed 600 or 1000cc bike that converted to efi would have the same issues unless using the R6 throttle bodies with the CV slides.

Don, I have been thinking about your idea of mounting the injectors in the needle jets also and spraying onto the underside of the slide. Though I really only want to keep this as an option if I can get hold of a second set of carburettors for handy money. I would like the option of returning to stock if things dont work out.

Hi, Thomas.

You might consider a Frequency-to-PWM converter, and use that PWM to drive a servo controller. Also, the secondary butterfly motor (the ones that aren't stepper type, anyway) aren't exactly +12 / -12, but are rather driven by an H-bridge. The idea in my mind (that I've yet to execute and test) for EXUP servo control is to scavenge a controller card from a $10 hobby servo (most of these are 6v, and will take the 5v PW signal from the MS quite happily) and use it to drive a 12v H-bridge.

The up-the-nozzle conversion I have in mind will hopefully be as purely bolt-on and bolt-off-reversible as the down-the-slide conversion that the Roadstercycle guy did. The other option might be to mount the injectors above the carbs entirely, spraying through the throat and leaving the carbs entirely stock. heck, this might even give you a "limp-home" capability, if all you have to do is turn the fuel to the bowls back on!

If you're using the OEM coil packs for timing info, I assume you're going fuel-only? What tooth pattern does this bike have? If you do go coil negative, EWFlyer made this post a little while ago: http://www.microsquirt.com/viewtopic.ph ... 86#p151772. It apparently gives a gloriously clean square-wave signal ...

I believe you can only learn from other people's perspectives on a given problem, so here's a link to something that's been going on in the Kawasaki EX-250 (baby ninja) community. http://www.ninjette.org/forums/showthread.php?t=74579

A guy named Matt running a company called Ecotrons has developed, tested, packaged and is now marketing a relatively cheap do-it-yourself fuel injection system for the Kawasaki EX-250. The link is to a thread on the forum at ninjette.org. I thought it might be useful/interesting to you to see what a $500 (US dollars) fuel injection kit looks like and also give you an opportunity to watch a bunch of fuel injection newbies work through installation issues. You'll see that some of them don't have any idea of the concept of a "clean install."

If you go through the pages of this forum thread I think you'll be able to tell which poster is me (for better or worse).

Yeah I was thinking they could also be PWM controlled. All this is purely guesswork. I really won't know the parameters of the secondary butterflies until I have a set of throttle bodies in my hand and can do some tests on them. For simplicity sake I think I will try to remove them first and see how the bike runs without them. Probably not very well but there is only one way to find out!

The plan is to run fuel only to begin with. Its the main reason for going the MS route and it will be easier to tune and troubleshoot when running the stock ignition curve. If theres one thing I learned from these projects is that you only change one variable at a time. I would like to look into letting MS handle ignition timing at a later date alright since I believe there is potential for a better topend through a different curve. I had planned on using the coils to read the rpm from just because its a simple setup and the coild are easily accessible but since the CBR uses an 8-1 ignition trigger wheel on the crank, I may use the signal from that for rpm. That will make less work when changing over the ignition control also. Thanks for the link to EWflyers post on the rpm readout. Very helpful!

I would be curious to know how you would do the up-nozzle injector placement! Looking at my carbs, I can't see how it would be possible without some irreversible modification to the carbs... I thought about fitting the injectors to the carbs after the throttle valve also but I just dont think there is enough meat there to allow it. Although it may be possible to make up adapters to fit instead of the rubber manifold boots which have an aluminium midsection that the injectors would fit into and the spray could be directed down the intake. This would involve moving the carbs back a bit though and so I'm not sure if the standard airbox would still work. Space is also a concern down by the engine head iirc... So many possibilities but which is the right solution?!

Thomas,

By removing the nozzle (and needle, obviously) there should be enough room to spray without much interference; the injector body, if it doesn't fit inside, will have to be mounted in the bowl area - the bowl, floats etc would be removed and an adaptor bolted on. The FZR carbs have this great big "jet block" that can be removed, leaving a relatively large passage in which to fit the injector.

Don, I see what you mean now. Though I'm not sure if it would work that well on my CBR... My main jet and emulsion tube are the only things that come out and the passage is not very big (probably 6mm). It also meets the needle jet at an angle so the spray would need to turn a corner as well as flow through a pretty narrow passageway. I can imagine that quite a lot of wall wetting will occur and although the fuel travelled the same path before efi, I just think it wouldnt give the full benefit of efi... I may return on the idea yet though! To give you an idea of location and size, heres a picture of the float bowls in the mc22 carbs. The main jet is in the middle and the end of the needle tube is beside the float hinge. Scale-wise, the hex head on the emulsion tube is 7mm.


Greg, thanks for the link! I must admit I cheated a little since I googled any info on your EX-250 project after you mentioned it to me first so it wasnt too hard to pick you out! That is quite a neat kit though for a good price. And the setup once the system is installed on the bike seems very straightforward too. The guys that installed it don't seem to have an indepth knowledge of efi systems and it seems to work fine for them. I'm not looking for pnp with the CBR though. I'm not worried about the cost of the project either. (as long as it doesnt run into ridiculous sums of course) Ive already put more money into the bike than it is worth! I am an engineer by profession and working on and experimenting with my bike is my hobby. I'm doing this to learn about efi systems and hopefully to improve on an already fantastic bike. I know its not going to be all plain sailing and thats all part of the challenge! If it was easy, I wouldn't be thinking of doing it!

The good news is that I got dimensions of the CBR carbs so I can compare to the GSR400 TBs and see how much modification needs to be done. And its quite a bit as I suspected but then nothing is impossible! CB400 TBs are out anyway doe to a larger stub OD. To give you an idea:

Dimension CBR250RR carbs GSR400 TBs
Stub ID 30mm 30mm
Stub OD 37mm 37mm
1-2 29mm 38mm
2-3 29mm 42mm
3-4 45mm 38mm

Completely off the subject but the first things my eyes always go to on a set of Keihin carbs are the "phillips head" screws, because they're not phillips head screws. They're JIS screws.

Just look at that poor tortured-looking screw head in your uploaded picture. Partially "cammed-out" and looking like it's not up for much more abuse before it gives up completely. It's a wonder the little things don't produce little screams of terror when somebody comes at them with an english/american phillips type of screwdriver.

And I'm willing to bet that screw-head in the picture is one of the better looking ones on those carbs. Which leads us to wonder, "Why do carbs stay in abusive relationships?"

That screw head looks like the UK Pozidriv. Philips drivers make a mess of them too. But Pozidriv isn't nearly as bad to a Philips head.

Haha! Yeah they were all pretty bad alright. Whoever was at them before did a good job of trying to make sure they wouldnt come out again! Replaced them with allen head screws though so its all good. Theres no need to stress about going at them anymore. Trekkie they are JIS alright. They had the little indent on the head beside the crosshead.

A short update on where my thinking is going... I've been researching the issue of secondary throttle valves and controlling them using an rpm based frequency signal. I havent made much progress on the electronics side but I have come across several cases where guys removed the secondary throttle valves on standard GSXR 600s and 1000s and claim to have gained power and response in the mid-range. They also report a lack of off-idle and low rpm response.

Since I will be removing the secondaries anyway to allow me to modify the spacing of the GSR400 TBs, I think I will leave them out to start with and see how the bike responds to having only the primary butterflies to control air intake. If I end up losing response or power below say 6k, then I cant see that as a major problem as the nature of these engines sees them revving above 6k for 95% of the time anyway. But then if it turns out that the bike runs like a dog and is totally un-tunable without the secondaries, then I can just as easily refit them and work on a way of controlling them off the rpm signal.

Its time to find myself a set of TBs and start modifying them!

Going off topic a bit here but just to keep it all in the same thread... What is the deal with sourcing injectors to fit certain throttle bodies? I mean injector physical size and fitting rather than flow rate. I have searched a lot and cannot seem to find any info on this. Do injectors tend to be standardised in the way they fit into throttle bodies? I suspect not since Ive seem pictures of injectors of all different shapes and sizes.

But do vehicle manufacturers tend to use the same types of injectors? As in if I buy suzuki SV TBs will the injectors from a GSXR fit the SV TBs?

The reason I ask is I have my eye on GSR400 TBs for the past few weeks but they keep coming up without injectors and fuel rails. Fuel rail is not a problem as the standard would be ditched anyway but it would be handy to get the injectors with the TBs. Since they are cheap without injectors, how will I know what injectors will fit the GSR TBs so I can at least start searching for them?

Cheers guys!

Hi, motthomas. Sorry to post in a necrothread, but I can't read or respond to your PM. What can I do for you?

Hi, Thomas.

A little off-topic, but here's the circuit you were asking for: