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What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sat Apr 09, 2022 2:33 pm
by Syscrush
Hey all. Looking at photos and parts fiches, the CB1100F and CBX carbs look really similar, at least superficially. I thought that looking at the fiches on Bike Bandit would let me compare part numbers of corresponding components, but for whatever reason the parts diagrams are broken down completely differently for the 2 bikes.

As far as I can tell from my research, the CB1100F used 34mm Keihin CV carbs, as compared to the 32mm used on the CBX. Looking at the CBX carbs here at my desk, it looks like there's enough material there to bore them out to 34 without issue - even the throttle shaft bushings stop about 1mm shy of the bore.

It has me wondering if anyone has built a rack of 6 CB1100F carbs for a CBX, or bored out the CBX carbs to 34 and fit CB1100F throttle plates.

Re: What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sat Apr 09, 2022 6:24 pm
by CBX-tras
The bodies of the 1100F carb won't let you make the bend in the middle and don't have sync ports for starters.
However, I did know a fellow in Ontario that did bore out CBX carbs. But, I have no knowledge how that experiment worked out.
Keep in mind too about the airbox and filter box that are critical for proper vacuum signal for the CV carbs. 1. the Airbox wasn't designed for larger air volume and 2. If you don't have an airbox at all they probably won't work correctly either.
It's all a crapshoot and you might end up destroying a good rack and wasting a bunch of time doing it.
The stock CV carbs w/airbox on my 3mm over on the CBX in my avatar ran perfect and performed well after I did some special mods to the inlet of the airbox.
If you're going bigger than 3mm, just go to round slides w/pods. No airbox, no muss or fuss.
This was 10 years ago, 100mm K&N filter:

Re: What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sat Apr 09, 2022 6:40 pm
by CBX-tras
The other thing you might what to consider is that if you get the head to breathe more efficiently, that should be the first step, not the carbs.
Cut the seats and fit 900F/1100F valves in and out. Do some porting work. Change the cams. Degree the cams. Make certain the left and right are exactly in time with each other. (The oldham couplers can be off). Lighten and balance the crank. Get better rods. Have pistons made to maximize the combustion chamber.

More horsepower to be made there than the carbs.

Re: What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sat Apr 09, 2022 7:35 pm
by Syscrush
Thanks so much for all of the info. I'm not looking to upgrade my carbs, I just noticed the similarity and was curious if this was a route that others had taken or not.

I'm working now on the next version of my design for EFI throttle bodies to replace the OEM carbs, and did some research into the different variants of the Keihin CV carbs as part of that, which led me to the 34mm version.

Do you know if the 34mm plates are available anywhere as a replacement part, or are old CB1100F carb racks the only source for them?

Re: What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sun Apr 10, 2022 8:22 am
by CBX-tras
Throttle blades were never available separately, for any model from Honda.

Re: What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sun Apr 10, 2022 2:22 pm
by Syscrush
I thought so, thanks very much for the confirmation.

Re: What are the similarities and differences between the CBX and CB1100F carbs?

Posted: Sat Apr 16, 2022 10:28 pm
by AshishNJ
JR - I also have the same filter on my cbx and I cut an hdpp ring exactly the same way and sandwiched it between filter and cbx. Runs much better and consistent than without