Motorcycle Repair: Throttle and idle, throttle return spring, honda nighthawk

Question
Hello,

I have a Honda Nighthawk 650SC 1982.  I just replaced the rubber vacuum T-connection for the 1 and 2 carburators since it had cracked with age.  Now the engine runs great and all four cyclinders seem to be firing again, however it idles at 5000 rpms and will redline well before I've opened the throttle all the way.  It acts as if the throttle range has shifted by 4 or 5 thousand rpms.  I may have stretched one or both of the throttle cables when taking off the carburator, but I don't think that is the problem since after looking, the throttle return spring is still moving the throttle back all the way when I let off the throttle.  I took the carburator off again and looked at everything and couldn't find any obvious problems.  The idle adjust screw is far from even touching the throttle mechanism so that cannot be a factor.  How could the bike idle at 5000 rpms when the throttle plates are closed all the way?  One important note is that when installing the rubber T-connection I had to separate the 1 and 2 carborators, which the owner manual warned not to do, could that have affected the synchronization since the adjuster screw in-between those two carburators was seperated?  I don't know what to try next, I'd sure appreciate any help or ideas.

Thank you very much,

Jeff

Answer
Hi Jeff,

Q: "... How could the bike idle at 5000 rpms when the throttle plates are closed all the way??"

A:  Synchroniztaion out of adjustment or intake air leak.



Q:  "... One important note is that when installing the rubber T-connection I had to separate the 1 and 2 carborators, which the owner manual warned not to do, could that have affected the synchronization since the adjuster screw in-between those two carburators was seperated?"


A:  Yes. Ensure the synchronization adjuster assemblies are assembled properly and then synchronize the carburetors.

Respectfully,
Mark Shively