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Discussion Starter · #1 ·
Besides there being 4 of them instead of 2 is there an actual difference between the Keihin carbs on the old CB750's & our CX500's?



Cycle X has a replacement carb system that replaces the 4 aging carbs on a CB750 with 2 new carbs & I wondered if that meant that 1 of those carbs could replace the set of 2 on my CX500.
 

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Maybe with jet changes but I would think that as the CX carbs are feeding {nominally} 250cc each and the specific cylinder size on a 750/4 is approximately 187.5cc you would be undercarbed. Jet changes aside the 750/4 carbs probably have too small a throat size anyway.

I'm sure there are others on this forum with more knowledge of this sort of thing than I have but I wouldn't attempt it.

Although, if they even fit you may have better fuel economy but of course at the expense of power. A smaller carb throat may even give better response at small throttle openings due to a higher venturi velocity but I think it would likely turn to c**p at larger throttle openings possibly even raising the spectre of engine seizure due to an overly lean mixture.

My 2 cents.
 

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There are way too many differences to overcome to try and use the 750 carbs. And the internal jetting and air bleeders isn't the same. It's not worth the effort. I agree with CXphreak that they are too small to be effective. And, the smaller venturis on a bigger motor will actually pull too much fuel through them due to the higher vacuum demand. They would end up running way to rich as well. Those carbs would think they were being told to deliver fuel for a higher engine RPM than you really are.



Why not just fix and rebuild what you have? When their cleaned and running right these bikes run strong and impressive.
 

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Discussion Starter · #4 ·
There are way too many differences to overcome to try and use the 750 carbs. And the internal jetting and air bleeders isn't the same. It's not worth the effort. I agree with CXphreak that they are too small to be effective. And, the smaller venturis on a bigger motor will actually pull too much fuel through them due to the higher vacuum demand. They would end up running way to rich as well. Those carbs would think they were being told to deliver fuel for a higher engine RPM than you really are.



Why not just fix and rebuild what you have? When their cleaned and running right these bikes run strong and impressive.


Thanks. Gonna clean & rebuild the ones I have using your guide.




I was just poking around & figured that while it was a long shot, it was worth asking.
 

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I agree, no harm in thinking outside the box! It's done good for me so far.
 
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