Strange RPM bursts 1982 CB450SC

Hey there
I have been rehabilitating a 1982 Honda Nighthawk CB450SC.  It was having serious hesitation issues between 3-4 k rpm so I did the “radioshack washer”* carb fix to lift and stiffen the needles.  THe hesitation went away and the bike rides wonderfully accept right before I need to downshift and the bike is under load.  Under these conditions, the rpm’s will suddenly jump from 3k to around 4.5k with NO increase in power.  It is almost like the clutch is slipping.  The clutch seems sound in every other area though, it has never slipped on me otherwise.  I have only experienced this issue while riding in 25-40 degree weather because I only bought this bike in late Nov. and havent had the chance to ride it in nice weather.  This problem is relatively consistant.
I would love to hear your thoughts and suggestions.

*THis trick involves taking a #4 size RadioShack brand washer and installing it at the base of the carb needles inside the needle housing.  The washers are secure and lift/stiffen the needles.  THis year bike had a TSB for the needles which were inappropriately sized and caused hesitation issues on the 450.

Thanks for the washer tip!!  big_smile

For jumping RPM under load – that doesn’t make sense unless the clutch is slipping. If the bike is decelerating and the engine is under load the rpms should never jump, and if the clutch slipped in this situation the RPMs would go down. Perhaps you aren’t clarifying the issue correctly. In 4th gear with the throttle pegged under hard acceleration the clutch doesn’t slip, correct?

Correct, it does not slip.  To clarify further, it seems like the engine is getting  fuel as I accelerate then around 3-4 rpm the it stops accelerating holds constant power then gets a surge of rpm.  There is a 1-2 second delay and then more power comes on.  THanks for the reply, I am quite enjoying your blog and your pictures, especially the HDR’s.

Sounds exactly like hesitation due to poor jetting to me. You said in your first post you cured that issue completely, but sounds like you didn’t. It’s a carburetor issue for sure, jetting seems most likely since you have been adjusting things.

Evan Fell

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