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Hi, i have an Honda CB450 and i have a couple of CB500t carburator that have an additional valve (cutt-off).
what are the differences? can I mount them in the 450? do I get any improvements?
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There is no performance improvement for the 500 carbs with the air cutoff valves. The purpose of the valve is to enriches the idle circuit when the engine decelerates. What it does is cut off the pilot air to the idle circuit. This is like closing the pilot air screw every time you close the throttle when the engine is decelerating. It eliminates the popping when you close the throttle. It allows a leaner main air mix in an effort to get to a lower emissions.
 

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What Jim said...

Although the CB500T carbs do have vacuum ports built in so syncing them is easy peasy. I prefer the 500T carbs for this very reason.
 

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What Jim said...

Although the CB500T carbs do have vacuum ports built in so syncing them is easy peasy. I prefer the 500T carbs for this very reason.
I just feel the exhaust to sync the carbs, I like the intimacy with the bike :)
 

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I just feel the exhaust to sync the carbs, I like the intimacy with the bike :)

I could say something but I will refrain. This is a family friendly forum after all LMAO
 

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You would also want to look at the jetting dependent on the year of the bike as even on the 450's it changes
 

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I just feel the exhaust to sync the carbs, I like the intimacy with the bike :)
I used to do this until I decided to drill vacuum ports in the head, once properly synced it was like a completely different bike.
 

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Anybody know what one might want to use to get started? I've got a 76 500 that I blew the engine on and have a 74 cb450 that I'm dropping in as a full replacement. I'd prefer to keep using the 500T carbs as I know they are good... the 450's would (probably) need a full rebuild.
Thanks!
Toran
You would also want to look at the jetting dependent on the year of the bike as even on the 450's it changes
 

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use the CB500T carbs. They're better than the 450's since they have the vacuum sync ports already which makes tuning a breeze.
 

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For balancing the carbs? No, you need a manometer.
 

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If your tester can read low vaccum then yes, you will have to read one side and then the other. Then make an adjustment then read again back and forth until you get it as close as you can get it.
 

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odd, my mightyvac wouldn't register anything when I tried it years ago.
 

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you COULD probably use one of these as well.




IMO it would still be easier to just drill the sync ports or better yet use the CB500T carbs instead.
 

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I tried the uni syn, won't fit on both carbs on a 450 and couldn't get it to seal on the carb it would fit on. I forget what was in the way. Battery box?
 
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