BiKenG

Already done that, but they're still not showing up. Never mind, I've gone off the Triumph idea. I'll be modding a 916 wheel to fit the NC30 axle instead.

Oldish topic, but found it while trying to find some info about the Triumph rear wheel. Unfortunately none of the pictures posted by YoshiHNS can be seen, so perhaps someone could help. What is the offset of the Triumph (Sprint) 3 spoke wheel? I.e. the distance from the centre plane of the rim to the hub mounting surface. All the chain driven VFRs have a -19mm offset, but what offset is the Triumph wheel?

Those sensors would stop the spark and/or fuel, so if you have those, the sensors are unlikely to be at fault. Likewise the pulse generator must be working. Is it firing at all or just simply turning over? Basically, if you have air, fuel, compression, spark, and they're occurring at the right time, the engine must run. So one of those factors must be missing or wrong. Do you have a clip-on strobe light? Really useful to help diagnose ignition/timing issues.

Good to know. Thanks for that. A typical Honda MAP sensor (I just checked for the RVT1000) is £256. So for the CBX, that would be prohibitive. I also have a VTR1000F FireStorm (er, Super Hawk in the US?) that I'd like to inject. So another project to keep me busy. Possibly do that before the CBX. Just see how everything else pans out.

Yes, I've read most of it, but a power cut here prevented me from finishing it. I will go back and read the rest though. It has encouraged me to start looking again at adding CNC capability to my mill. That would be enormously helpful in so many ways. But I digress... I understand that modifying the TBs to suit won't be trivial, but Patrik and Durbahn both use the TBs from a totally different bike and then had to totally create their own maps etc. from scratch. I am currently of the opinion that using 5th Gen TBs will not actually be as difficult although I may change my mind once I start hacking them. However, if I can get the TBs to fit, the rest of the system is essentially off-the-shelf, just by using the 800 parts and it should even run like that with just minor tuning required with a PC. All that is a BIG advantage by using the VFR800 parts. I do have to add a Cam sensor, but that's been done before. Of course the first requirement is that I can get the TBs to fit and I'm waiting on a set of 5th Gens I can start work on. Currently I'm firmly of the opinion that it will be easier than modifying the carbs, but I guess I'll soon be finding out if I'm right or wrong on that. It's all good clean fun though.

I see, so there's a MAP sensor for each cylinder. I have a funny feeling Honda MAP sensors are rather expensive, but I guess he's using a more cost effective sensor. All food for thought re the CBX, but is another reason for grafting the 800s injection onto the 750 as provided it can physically be done, then it's relatively simple as there's a ready made wiring harness with all the required sensors and just the one ECU module. No other ancillary electronics required. Well, apart from a Power Commander or equivalent. At least I assume it will need some tweaking, although just have to see on that once it's running.

Aha, I've been thinking along those lines too, using the VFR750's carbs and I believe an early Kawasaki 900/1000 (I forget which) had a similar injector rail with suitable injectors. I've not discounted it and will be looking into that and the MicroSquirt for a similar project to inject a CBX1000 (6 cylinder), but that's further down the line. For this VFR750 I kinda want to make it as Honda as possible, so priority will be to see if I can use the 800 parts. If I can't use those TBs, I'll look for alternative TBs and if that fails, then it's modify carb time and a different ECU. But it's always interesting to see what others are doing to inject their bikes, even more so with regard to my CBX project. How does the MS use MAP sensor output to detect engine position? If the MAP sensor is connected to all intakes, how does it know which pulse is for which cylinder? BTW, why did you choose the MS over say Motec?.

Aha, first of all, yes those TBs will be perfect to try and fit, thanks, much appreciated. Secondly, very interested to hear what you say about the 3rd Gen carbs being bigger - music to my ears. Since 4th Gen rubbers are too small to accept the TBs, there's hope that 3rd Gen rubbers may be better, i.e. actually fit. I need to find a good (i.e. flexible) set of 3rd Gen rubbers and try to squeeze those TBs in.

Puzzling that despite what JZH's picture seems to show, those TBs on the right will NOT fit into the intake rubbers for the carbs on the left as the TBs are so much bigger. Really doesn't look that way in the photo. Mind you, I was trying it with 6th Gen. TBs. Could they be bigger? But it does explain from where I got my previous optimism about splitting the TBs. The 5th Gen. TBs as shown above are the ones I first thought about splitting and it looks entirely feasible. The 6th Gen. ones, not so, hence my more recent less optimistic, post. Not only are the castings less favourable to splitting, but also the upper intake connection to the airbox is siamesed on the 6th Gen, but separate on the 5th Gen. which is far preferable. No reason to not use 5th Gen. TBs on this 750 project so I just need to find some 5th Gen. TBs to cut. Don't 'spose you want to sell yours John? As far as I know the 6th Gen got 8 point injectors but then upped it to 12 point in 2006. At least the parts list shows different part numbers for the injectors themselves which supports that. However how can one distinguish between TBs with 8 point injectors and the later TBs with 12 point injectors. Obviously counting the injector holes would be tricky, but is there some other way to identify TBs as early or later 6th Gen? One other question to which someone might know the answer - Is it possible to fit the later multipoint injectors into the 5th Gen. TBs? Usually the whole TB is swapped if you want the later injectors, but would they actually fit? I suspect not, but don't have both here to try it. Anyone know the answer?

Taking a good look at the 800's TBs, the way they're cast is not how I remember from previously and separating them won't be as simple as I thought. May be impossible depending on if there's any internal cross passageways I cannot see. Hope not, but anyway I started looking at alternative TBs. First of all I discovered that the 929 FireBlade seems to have 2 pairs, just like all the other Hondas and not the 4 separate units as I have seen stated and as I mentioned in a previous post in response to Mohawk. So whoever wrote that is simply wrong. As Durbahn discovered, the GSX-R750 is a good candidate with 4 individual TBs. But at 45mm intake ID they'll make the rubber matching problem worse. Unfortunately, although the GSX-R600 uses smaller TBs that might fit nicely, they also use ECU controlled secondary butterflies and that's just not gonna work with the VFR. So nothing's falling into place at the moment:-( Just have to keep looking.

Fallen at the first hurdle unfortunately. It would appear the 800's throttle bodies are significantly larger than the 4th Gen carbs :-( There's no way that I can see the injection TB fitting into a 4th Gen intake rubber. I pushed hard but it's not even close. Also the internal shape is wrong as it partially obscures the actual injector. The 800's intake rubbers are shaped around the injector to not obscure the fuel pulses, but of course the RC36 intake rubbers don't have that. I also tried to fit the 800's intake rubbers onto the 4th Gen intakes. It's closer, but not ideal. They slip on very easily of course as they're basically too big and they don't grip the intakes at all. There's a mm or more of movement side to side - until you tighten the clamp screw. It is actually possible to squeeze the rubber onto the intake stubs. They're then quite firm although it is possible to twist them around if you grip them well and try hard enough. The stubs seem longer than the 800's as the rubbers are not snug up against the head. There's a gap. However, that wouldn't matter if the rubber can form a good tight seal onto the stubs. I think a better type of screw clip would have a better chance of getting a good seal. But I'm not sure of the long term implications of the rubber being compressed like that and whether any possible good seal would last. So, 4th Gen intake rubbers are a non starter (damn, just wasted £25 on them) but 6th Gen rubbers are a possibility, although not ideal. So the search is still on... Do any of the pervious carb models have a larger intake/carb diameter than the 4th Gen? That might help.

What's the difference in the intakes of the VFR versions, i.e. the Gen 3 to 6? I'm pondering the possible fit of throttle bodies and intake rubbers. Have 800 TBs varied in size over the years? I know the injectors have changed a couple of times, but what about the intake sizes, have they altered at all? Likewise, did the carb size change between the 3rd and the 4th Gen bikes? I have some 800 TBs (late 5th Gen and a 6th Gen) and will soon have some 4th Gen intake rubbers to compare to. But I've no obvious way of knowing if there were any differences from the items I have, without buying one of everything of course. I suspect all the 800 have the same size intakes and likewise the RC36 models, but can anyone confirm or refute this?

I'm not convinced they would be simpler. I'd have more to do figuring out how to assemble them in the correct rigid layout. Besides, I really think the larger choke diameters would not work in my favour and require far more of a change to fuelling from a basic 800. Probably a better option would be to use those from a CBR900RRY (929). They are similarly separate units, 40mm and also from Honda :-) At the end of the day, I'll probably use whatever best suits the RC36's inlet tracts and rubbers.

First step will be to find out if the 800's throttle body will fit the 750's intake rubbers. But I don't have the 750 engine to hand at the moment so it'll be a few days till I can do that. Another thought. The RC36 intakes changed size did they not, from 3rd to 4th Gen? Are the rubbers also different?

That's what Durbahn used, but he no doubt wanted power so the GSX-R's 45mm throttle bodies were appropriate. I always try to use Honda designated parts if possible and I have a spare set of 800 throttle bodies, so that's a big incentive to make use of those. One reason to NOT use those is that they are cast together in pairs which means trying to change their relative spacing would appear to be harder. But, on the other hand, the cast 'web' between each choke in a pair could be cut and then used as the mount on to which could then be bolted something to space them as required. Since these webs look kinda flat, that might open up the way to use some simple carbon fibre sheet cut to size which would be stiff enough and nice and light. Then something else between the spaced out pairs to suit the V and intake angle of the RC36 motor. A big plus is that with the 800's throttle bodies, injectors, ECU, sensors and wiring, it ought to run. A PC can then be used to clean up the ignition and fuelling. Simples But still just tossing ideas around in my head at the moment.

If the throttle bodies are close enough to the carb's diameter, it ought to be possible to just use the RC36 rubbers. That part number is I think wrong, but if you can let me know the correct part and I can look into getting one for you in exchange for the loan of the carbs in order to get it to first run.

Ah, so clearly the carbs are a larger bore than the injectors. Hmm. Durbahn used GSX-R 750 injectors which are larger and may therefore be better. But, I am more interested in mid range torque and ride-ability than outright power, so the smaller injectors might be a better bet. They flow enough for acceptable power on the 800, so really, they should be enough on this 750. Re-joining the bodies for the different spacing and angle will be one problem, but the intake rubbers will be another. Durbahn had some specially made. That'll be something to consider at a later date. In fact, if I use the throttle bodies with the same OD as the carbs, I could use the 750's original intake rubbers. You know the next question John. Could you possibly measure those ODs? How well would a throttle body fit in the 750 intake rubber? BTW, this is not a short term project. I also have several others I'm working on and this is more a case of as and when I get time. So don't expect rapid progress.

The dash is really simple and the ECU doesn't care about whether it's connected or not. I've not decided on dash for this bike yet, but won't be OEM VFR. I'm building this from a separate engine and frame (that I already have), so I'll just buy the bits I need rather than butcher any existing bike. The FI system requires a CranK Position sensor and a CaM Position sensor. The former will be very accurate to determine the exact position of the crank. The latter will be far less so, but is required to establish on which part of the stroke the engine is on as that cannot be determined from the CKP sensor output which is used to provide the ignition timing. The ECU can simply control the timing of the spark relative to the CKP sensor output, but also knows when it's TDC and when it's top of the exhaust stroke from the CMP sensor output and in this way there's no need for any wasted spark. What I'm not sure about is how it decides when to open the injectors. That's less critical than ignition timing and could use the less accurate CMP sensor output, but I think it's more likely that the CMP sensor is only used to determine the stroke and it's the CKP sensor output that is used to accurately determine when to spark and/or squirt. However, to a certain extent it's irrelevant. There will need to be CMP sensor and I'll need to figure out how to add that. Durbahn's site will help there as he's done it for the RC30 and a 400. In any case, assuming the ignition pulse of the 750 can be used as the CKP sensor output the CMP sensor is the only one that needs to be added to engine. I was thinking of using an 800 fuel tank, which has an internal pump of course. Might drop straight on. Anyone tried this? I'm not imagining any of this will be simply swap and fit from other bikes. I WILL have to manufacture parts for the throttle bodies assembly and the cam will need welding etc, but I have the equipment. There are various ECU options if I don't go with the 800's. Durbahn used Motec and could provide ready made working maps to start from, but there are others, although probably have to start from scratch creating the maps. I still think the 800 ECU and a PC would be the simplest.

I thought about and looked into that, but it wouldn't be trivial. Cut the S/A pivot boss off the back of the 800 engine for starters and then most of the mounting points don't line up so quite a lot of reworking the frame to make it fit. Even then you'd have to mess with the airbox, so no advantage there. But also, I like the idea of the 750 engine. Nicely symmetrical compared to the 800 and I think a fun project to inject it. Don't get me wrong about the 800 engine. I do like that also and have other projects going on involving a couple of those, so in some way, I also wanted this to be a 750 to differentiate it.

Hey Keef, I've been telling him that for years now.