Topic: 1974 CB750 Carb help

[Jcop.550]

Looking for some help/guidance on a carb issue I’m having. First time doing these round top cb750 carbs so I’m a little stuck.

Cleaned and rebuilt these carbs and put them all back together. When the slides are down (1st picture) they are really stuck in there and take a good bit of force to slide again. Once they release they don’t fully  go back down to the point of where they get stuck and are sitting too high (2nd picture) ….or is that where they should sit? They should be lower, right? And not get stuck that low, and move freely of course.





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[newday777]

Did you put in carb kits and their new brass? Or did you clean and reuse the original brass parts?

[Jcop.550]

Did you put in carb kits and their new brass? Or did you clean and reuse the original brass parts?

Yes all new brass


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[HondaMan]

I very STRONGLY suggest you put the original brass back in. There is no aftermarket brass that runs (nor fits) correctly in these carbs.
The problems with aftermarket brass (K&N, K&L, Keyster and others) ranges from the mixture running so lean that the bike performs badly and will burn exhaust valves to sticking the slides open because the new needles are too thick for the OEM needle jets. That can make the slides stick open. It also completely cuts off the fuel while doing it, which causes the lean condition that damages exhaust valves.

And, the bike will run like crap.

[Jcop.550]

Thanks for the input guys! Problems solved: needle jet holder was too tight causing the needle to stick. Loosened it a little and they move freely now and sit where they should.


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[BenelliSEI]

That suggests the needles were sticking in the jets. Loosening them really isn’t a solution. Do you have the old needles? Put them back in.

[newday777]

Did you put in carb kits and their new brass? Or did you clean and reuse the original brass parts?

Yes all new brass


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Hondaman's answer is why I asked. I hope you saved the old brass pieces.

[M 750K6]

My 750 didn't run properly until I put the old needle back in. Too rich in my case. Keyster branded replacements. Shouldn't be sold until they get them in spec.

[HondaMan]

My 750 didn't run properly until I put the old needle back in. Too rich in my case. Keyster branded replacements. Shouldn't be sold until they get them in spec.

Sadly, they have been that way since they appeared in the 1990s.
They have been recalibrated several times at K&N and Keyster (that I have witnessed) and somehow still never came close to being right. Strange, since all they needed to do is copy a set of original parts.