Weighing Fueling Options

[Syscrush]

Phil: I think the worst thing you did was park your bike! You need to get on that thing and ride.

Words of wisdom here.

But as much as I love it, I consider it unrideable right now. The fuel consumption is so extreme that I'm really worried about building up problematic amounts of carbon, or (to a lesser degree) gas washing the oil from the cylinders as I ride. I could send the carbs out to Dave or Mike to get them dialed in, but at this point I'm not really interested in spending another penny on fueling unless it gets me closer to EFI.

How about this, to give you a few more sleepless nights...

That's interesting, for sure. Customized ITBs from one of the EFI conversions you covered earlier? It looks like they would run open or with pod filters - not the stock intake and airbox, I'm guessing.

[BiKenG]

...My first choice is to have a returnless system in the modified OEM tank, using the ECU to control the fuel pump...

I would agree with you on that, but how do Honda supply fuel to their current bikes? At first they used a regulator and return line, but now I'm not so sure and having been recently knocked off my bike and only just out of hospital, I'm not really in a position to do much in-depth checking. I've a feeling they still run a return line. In any case I'd say probably follow what Honda do. Not only are they pretty good at getting this stuff right, but it increases the possibilities of using OEM parts which always helps.

[Syscrush]

...My first choice is to have a returnless system in the modified OEM tank, using the ECU to control the fuel pump...

I would agree with you on that, but how do Honda supply fuel to their current bikes? At first they used a regulator and return line, but now I'm not so sure and having been recently knocked off my bike and only just out of hospital, I'm not really in a position to do much in-depth checking. I've a feeling they still run a return line. In any case I'd say probably follow what Honda do. Not only are they pretty good at getting this stuff right, but it increases the possibilities of using OEM parts which always helps.

As far as I can tell, it looks like most OEM setups from the last 10 years have a combination filter & FPR integrated with the in-tank pump.

[BiKenG]

...My first choice is to have a returnless system in the modified OEM tank, using the ECU to control the fuel pump...

I would agree with you on that, but how do Honda supply fuel to their current bikes? At first they used a regulator and return line, but now I'm not so sure and having been recently knocked off my bike and only just out of hospital, I'm not really in a position to do much in-depth checking. I've a feeling they still run a return line. In any case I'd say probably follow what Honda do. Not only are they pretty good at getting this stuff right, but it increases the possibilities of using OEM parts which always helps.

As far as I can tell, it looks like most OEM setups from the last 10 years have a combination filter & FPR integrated with the in-tank pump.

Just did a quick check as much as I can do now and discovered that the following bikes use external regulator with return fuel line:-

• RVT1000 (VTR1000SP-1 & 2)
  VFR800 Gen 5 and 6
  CBR900RR

Then they changed to using single fuel feed with built-in regular in pump assy. in tank:-

• VFR800 8th Gen
  VFR1200
  CBR1000RR

Obviously not exhaustive but gives us an idea. Honda obviously now believe that single line and built-in reg. is better. However, could we achieve either with an external in-line pump that would avoid having to modify the tank?

[Syscrush]

One option for converting the carbs to TBs is the way that mlynch001 has gone: remove the slides and float bowls, and machine injector holders into the float bowl replacements. Another option that I'm giving careful consideration is the approach used for these VMax CV to EFI conversion kits, helpfully shared by Gearheadgregg. That approach would be a bit less simple for a CBX than for a VMax, as the VMax has a perfectly round slide, while the CBX does not.

Well, gang, I've been giving this a lot of thought and done a fair bit of research, and I've decided in for a penny, in for a pound.

The path I've settled on for the throttle bodies is to design my own and have them fabricated. Fabrication will be by CNC machining or maybe 3D printing (DMLS aluminum printed parts are expensive and will still require some finish machining, so just going for CNC from the start is the most likely approach).

The plan is to design them such that:

1. They retain all of the OEM mounting points so that they can go in the OEM rack.
2. The inlets and outlets are the same as the OEM carbs, so the whole OEM intake tract can be retained.
3. OEM throttle linkage and balance/sync linkages will be used.
4. Injectors will be mounted from above for ease of service.
5. The two outboard TB's will be made to look similar to the OEM carbs. I'm not trying to make them exact replicas, just have them similar enough that they don't draw the eye.
6. The 4 inboard TB's will probably be just the simplest design that can accommodate the necessary parts and mounting points.

The benefits of going all-new custom TB's as I see them are:

1. I can get an exact fit for the OEM intake tract, which is very important to me.
2. Should be close enough to the near-OEM look that I want.
3. All-new parts will mean the elimination of many variables related to wear and repurposing of old OEM carbs.
4. Lots of freedom in injector placement to find the best compromise of rideability/tuning, service, and packaging.
5. There's definitely some bling factor.

Given that I'm not a machinist and would be paying someone else to retrofit the carbs in any case, I think that the cost of going all-custom might not be way higher than the retrofit approach. I can pull, disassemble, and clean the carbs myself, have them 3D scanned, and model the new custom ones in Fusion 360. Being able to do all of that on my own without using the time and expertise of a professional machinist should partially balance the cost of the custom CNC or DMLS fabrication. My plan is to do the models myself, have them printed in an inexpensive plastic medium so that I can do a test fit with injectors, plumbing, and wiring, and then have the finish parts made.

If I go with CNC, then I will let the fabricator handle the real expert CAM-related stuff like toolpaths - but starting from a validated model should make that not terrible. If I go with DMLS, then the detailed CAM stuff isn't required.

Now, if you'll excuse me, it's time to get back to watching Fusion 360 tutorials on YouTube.

[Syscrush]

I'm sharing this both because it's a very informative discussion of AFR in theory and practice, AND it shows the incredible power of modern EFI tuning on a closed-loop system.

He literally changes the AFR in 5 seconds between runs, with the engine running.

[wyly]

You're a crazy man with waaay too much money ...I hope you succeed then maybe we can all have EFI

[Syscrush]

You're a crazy man with waaay too much money ...I hope you succeed then maybe we can all have EFI

We can all have EFI tomorrow if we just go out and buy bikes made sometime in the last 20 years. :)

It's a big challenge, and as far as I can tell, nobody's done it well for a CBX that's ridden in a wide variety of conditions. The approach I'm planning on will take time and money, and there's definitely no guarantee of success. I am hopeful that the same careful and analytical approach (guided by invaluable help and info from my friends here!) that I took to getting the brakes and suspension to the very high level they're at will pay similar dividends to getting a viable, rideable fueling solution with all-new parts. A lesson that life has been trying to teach me over and over is to take the time (and other resources) to get stuff right. Shortcuts never pan out in the end.

As for too much money - I spent more on a beater SV650 that never worked quite right than what I expect to spend on the EFI conversion... The only money I've spent on my CBX that I've regretted all related to chasing my tail with carbs. So as long as I'm making some forward progress, I'll feel OK about what goes into this project.

Now I'm thinking about that old SV. I used to joke that if I had bought it and a new GSX-R600 on the same day and lit them both on fire I'd have come out ahead money-wise. But when everything on it was working right, it was an absolute treat. Too bad that was almost never.

[patzx12]

I am an engineer with CNC equipment I think about EFI conversions but this is my input to the debate,
Prototype one off design and machining takes ages.
First attempt rarely works and you will probably go to Mk11 and Mk111 versions.
Using subcontract machine shops is expensive and requires project management to keep them on track. Any good shop will have a full order book and a guy wanting bits made for a motorcycle would be low priority.
I am running 2 CBX at the moment, they only do a few 1000 miles a year, they are not my primary ride so if the fuelling is slightly off so what.
As it happens all i did was strip clean and balance the carbs with new O-rings and no replacement parts.
The bikes run great for what they are, the CBX was never bought for performance a 2 grand Blackbird would blow it away. If i want to cover distance faster on a ride I will take my 2016 BMW RT.
Having said all this i hope you go for it and keep us posted.
The only advice i would give is to buy a second running well CBX as a riding bike while you are developing the special.

[patzx12]

There was an EFI bike at the French CBX rally (3 years ago).
It was a tidy job but did not get to meet the owner.

[EMS]

The French bike is from Jean-Luc (last name?) and is one of two in Europe that run quite well and regularly. The other (2?) is owned by Stefan Jung quite a few years ago and I wrote an extensive article about it on CBXWorld back then.

[wyly]

The bikes run great for what they are, the CBX was never bought for performance a 2 grand Blackbird would blow it away. If i want to cover distance faster on a ride I will take my 2016 BMW RT.

I did buy my CBX performance bike it was best there was in 1979. Now I just want it to run as best it can be, better brakes, suspension, quicker. Also more efficient and less/easier maintenance. Sure I could go my favorite parts shop tomorrow and hand over $3K for a used GSXR 1100 that will do blow my Z away but that's not what I want. Some of us want bikes that are untouched originals, others slightly modified and still others highly modified it's very personal, practicality doesn't enter into it.

I could easily buy that GSXR 1100 for $3K instead I'm choosing to modify it's grandfather a 1984 GSX1150ef just because I can and want to not because it's practical or financially smart. I love the challenge building it more than handing over a lump of cash to have it done for me.

[patzx12]

I am with you on that. As a classic ride the CBX beats them all something special. I updated the suspension and brakes on my 82 but not too radical, I kept a 19" front wheel. I have done a lot of brisk miles on the bike it has to be ridden differently than a modern BMW. I once came from Spain in a day 2000km in 18 hours.
I built a 79 chassis with Suzuki GSXR600 rear (one of the few modern short swingarms, most are 550mm +) and B-King forks. I made billet triples to correct the fork offset.
I did not finish that project.
I am now completing a 78 with Suzuki V-Strom forks and wheels (19 front), these forks are plenty long. This bike is almost ready with loads of billet stuff.
I will but up a build post once i hear it go Vrumm- vrumm.

[Syscrush]

The French bike is from Jean-Luc (last name?) and is one of two in Europe that run quite well and regularly. The other (2?) is owned by Stefan Jung quite a few years ago and I wrote an extensive article about it on CBXWorld back then.

Thanks very much for this. Looks like the people to talk to about that red bike are Philippe Hanus and Jean-Luc Millet. Time for more digging.

I found this article. I also dusted off my French and had a short chat with Jean-Luc to get a few pointers. Thanks again to all for the invaluable info and advice on here!

[Syscrush]

This week I learned about Saturn's oddball "compression sense ignition":

The waste-spark ignition is part of a unique Compression Sense Ignition (CSI) system that allows the powertrain control module (PCM) to determine proper engine phasing (cam position) without the use of a separate camshaft position sensor mounted near a rotating engine member.

Here's the source.

At this point it's not clear to me if this approach could be applied to a retrofit installation like what I have planned, but if it's possible that would be excellent. Other than tuning, I feel like cam phase sensing is the biggest open question I have right now. An approach that would work without having to mount any sensors in/under the cam cover would be amazing.