Motorcycle Repair: Jetting Honda CV Carbs, jet controls, needle jet

Question
I need some expertise on jetting some CV style carbs for a ’71 Honda CB350K3.  I know that you can’t give me a specific jet size to make everything work but need some general information on them.  I just rebuilt the motor this last year and have ridden it around for 50-60 miles.  I can tell that it is running lean.  It cuts out when getting in the higher RPM range, above 4500 - 500 range.  I have also checked the plugs and they show a lean condition.  I can leave the bike idle and check the plugs and they look fine so I believe the idle circuit is tuned close, its just the mid to high range is running lean.  Book says to raise the needle and change jets.  I didn’t think these needles could be raised in these carbs like you could in a slide carb.  Is it possible to shim the needle up? If so, how much can you get away with?  I guess my real question is about changing jets.  Since these carbs have a secondary main jet and a main jet should I change both of them at the same time incrementally or should I start with one and then the other?  What would be the proper sequence of events?  I believe right now the carbs have #68 in the secondary and a #100 in the main. (I believe #105 was stock on these).  I should also mention that the exhaust is not original; they are some shorty mufflers that I bought to get it back on the road.  Original mufflers are not cheap and hard to come by it seems.  I believe the exhaust is the contributing factor to the engine running lean.  Thanks for your time.  I am excited to get this old twin on the road again.


Answer
Kevin, you are right it needs to be richened up.  You can get small washers from the hardware store to shim up the needle jet.  If you raise it about .040 that about all that Honda normally built into their stock adjustments.  You can also try raising the float levels a millimeter or two.  That will richen up the whole range.  The needle jet controls from 1/8th throttle to about 3/4 throttle.  The main jet controls the mixture from 3/4 to full throttle.  If you increase the main jet size the midrange will also richen up even if you don't change the needle position.  So I'd recommend you get the main jet set the way you want it and then adjust the needle jet to get the throttle response you're wanting.

Regards
Rich