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Discussion Starter #1
I am having an issue with carbs. After rebuilding both carburetors. New diaphragms and covers too. Fired up right away idle takes off upwards toward 5500rpms. Both carbs where bench synched and throttle synced on bike. After spraying carb cleaner around to find if air leak was suspect. Left side carburetor diaphragm top showed change in idle.

I removed top cap and cleaned reapplied gasket sealer to the new diaphragms and cover surface and reinstalled. I got the same result, so I cleaned and installed without gasket sealer, again same result.

QUESTION IS - is there something I am missing? as I spray carb cleaner around the diaphragm cap idle dips considerably, leads me to believe there is air intrusion. Is there a better way to seal these caps? Or something plugged where there is too much suction? Mind you these are new diaphragms and covers. Boggling the mind!

Thank you for any help
 

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Moved to 350 Fuel Supply and Carburetion section.

Did you pull the throttle plates off the shafts when you cleaned the carbs? Plates slightly off center on the shaft will leak air and cause a big idle issue. Did you re-grease the felt seals on the throttle shafts after the rebuild?
 

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Discussion Starter #3
Moved to 350 Fuel Supply and Carburetion section.

Did you pull the throttle plates off the shafts when you cleaned the carbs? Plates slightly off center on the shaft will leak air and cause a big idle issue. Did you re-grease the felt seals on the throttle shafts after the rebuild?
Yes, Installed new felt seals with grease and centered throttle plates. No change in idle, with carb cleaner sprayed on the shaft outlets.
 

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When centering throttle plates I've found the most effective way is shining a light from the opposite side and looking for an even gap between the plate and body, what I call a smile.
309343
 

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When centering throttle plates I've found the most effective way is shining a light from the opposite side and looking for an even gap between the plate and body, what I call a smile.
View attachment 309343
I'm having a similar sounding issue with my 72 cb350. When I start the bike it slowly rises to very high idle. Although it doesn't happen every time. I have done similar things to what OP said. OP, did you finally solve the issue. What did it?
 

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I'm having a similar sounding issue with my 72 cb350. When I start the bike it slowly rises to very high idle. Although it doesn't happen every time. I have done similar things to what OP said. OP, did you finally solve the issue. What did it?
While you're waiting for that answer, check your Conversations and post an Introduction for the community
 

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Discussion Starter #9
I think my issue is with syncing the throttle to each carburetor. I think I am close as I rev the bike throttle very slowly returns to idle.
 
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