Problems with Carburetion

FrenchBernie

New Member
Joined
Jul 7, 2026
Total Posts
2
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Location
Montreal, Canada
Good morning gentlemen & ladies
I have a carboration problem with my friend's Nighthank.
Long story : He started to have problems about 4yrs ago. Could not figure out why so he put it in storage in a garden shed for 4 yrs. He was looking for someone to rebuild his carbs.
It has 30,000 kms
So I said I would help him out. When we took it out of shed would not it would not even start, took carbs off ,dismantled they & soaked them in a sonic bath . Put them together & the bike started up with idle only. Could not get it passed idle. We were on the right track.
Ordered a carb kit, took them apart again and changed out parts that were needed. Now after several tries it will run but after 2000rpm it doesn't want to go in higher rpm. I have to hold throttle and give it gas so slowly & I can get it up to 5000 rpm but just barely. I am wondering if anyone has had the problem & how you went about to fix it

Bernie
 
Someone with experience with these carbs will be along shortly to help out. In the meantime, if you could provide some more details on your bike and what carb model you have will help.
 
Just confirming we are talking about a CB450sc Nighthawk? Any idea what the initial symptoms were 4 yrs ago when this started? If it was struggling at upper RPM range this could be an electrical issue. do you have access to a timing light? if so, might be a good idea to verify the timing advance is working before continuing work on the carbs. trouble at higher RPMs could be carbs or could be electrical, so it would be good to eliminate one of possible. you could also try your previous test by pulling the choke to see if richening the mix helps some, that may help identify an overly lean condition. see the link below for list of tests on the electrical system to help narrow it down

https://www.vintagehondatwins.com/f...sis-for-1978-86-cb-cm-400-450-manual-trans.6/

It also would help to know if everything else on the bike is stock, when you start messing with the airbox/air filter and modifying exhaust is when it really starts affecting the Off-idle performance for this engine.
 
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