Weighing Fueling Options
The bike has a +3mm overbore (near-stock compression), stock head, the correct 1979 cams, K&N filter in the OEM airbox (I'm open to going back to OEM if that will help the OEM carbs work best), and a 6-into-2-into-1 header with a baffled muffler.
Given the amount of back & forth I've dealt with in trying to get these carbs right, I strongly suspect that they're suffering from a mix of bad tune and problematic wear. It's been 5 years of 1 step forward, 1 step back.
I have been spending some time on the fence about how to proceed. I'm stuck between these broad choices:
1. Have the OEM carbs restored and set up by an obsessively meticulous CBX specialist. This is the simplest and most cost-effective approach and the one that gives me most confidence that the bike will look, sound, and work right. The concern I have is that after the rebuild there's still the matter of getting them final tuned on the bike, which has proven to be an ongoing challenge. And if they don't work right after the rebuild because of other factors on my bike (specifically the exhaust), or because I'm just not satisfied with the stock carbs even at their best, then what?
2. Aftermarket carbs - either the bolt-on CR setup from TIMS or a custom-built rack of Yoshimura MJN carbs. I'm not looking for more power, but these seem like the way to get everything fresh and new, with the potential for more power as a bonus. The drawbacks here are greater cost, and I don't like the looks or the sound as much - I also worry about the CR's being rattly and annoying for street riding, and about the MJNs not fitting (as nobody is making a CBX-specific application). Also, both are less common than OEM, so I worry about making it even harder to find relevant tuning expertise. I really do want to keep the stock airbox, which is presumably more difficult or impossible with these options. Lastly, it's not clear to me if either of those carb choices would make tuning any easier.
3. EFI conversion aka the nuclear option. I am tempted to go this way for 2 reasons - the first being that it can be tuned with a laptop and there's plenty of local expertise for doing that, and the second being that with a good closed-loop tune I could also add a catalytic convertor and leave less bad karma in my wake. The obvious cons are cost, looks, and complexity. I have not found an individual throttle body solution that's likely to work well, fit the CBX, and look good to me.
A bit more on EFI conversion options:
I have thought about gutting the stock carbs and building a plenum that looks like the stocker but with a single throttle body. The carbs would basically be just plumbing in that case. Injectors would have to be worked in somehow sneaky, which poses serious difficulties. I think that this idea is a non-starter.
I've also thought about trying to use the TB's from the Triumph Bonneville that are specifically designed to look like vintage carbs:
They look dandy, but I seriously doubt that 6 of them will fit into the space left by the OEM carbs.
Maybe a hybrid approach where the CBX carbs are gutted except for the throttle butterflies and those giant caps are hiding injectors?
The other class of options are all-custom solutions for throttle body, plenum & manifold, and airbox. Don't try to look stock, just try to look good.
I'm really torn on this, and open to ideas or suggestions.