Motorcycle Repair: CB350 cable routing, plug caps, slow jet

Question
Since I'm here, I may as well ask you this one too.  I'm having a problem with the left carb running too rich.  The right side looks good, at least the plug indicates a good burn, but the left plug is black and sooty looking.  I noticed that the jet needle doesn't appear to have an adjustment, so I'm not sure where to go from here.  Also, one of the jets in each carb has a rubber plug over it, (I think it's the slow jet) what's up with the plug?   If I could get a few minor things ironed out, I'd be really happy.   

Thanks again..
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Followup To
Question -
Bill,

I have a problem with the throttle cable routing on a 1970 CB350. When I turn the bars full lock to the right, the rpm goes way up.  Can you point me to a cable routing diagram or perhaps explain the proper route for the cable?  Does it go through the metal loop at the top of the handlebar mounts?   

There's nothing quite as fun as riding a 34 year old Honda to work every day!

Thanks..

Answer -
Honda actually issued a service bulletin highlighting the importance of correctly routing the throttle cable.

It routes in the space between the tachometer and fork bridge, then dives down between the two meters. It continues around the steering head, along the left side of the frame, ABOVE the fuel tank mount. DO NOT route it through the cable loop at the handlebar mounts.

That procedure should correct your throttle pulling issues, but always check it before you ride.

Congratulations on your "daily driver" ride!

Bill Silver

Answer
Patrick, do the basics first. Valve adjustment, compression check, check spark plug caps for excessive resistance and mostly the ignition timing before you dive into the carbs.

Once you have eliminated the other possibilities, then you can check the float levels.. varies as to what series carbs you have (number is stamped on the bodies). All of the rubber O-rings and plugs have to be secure and sealing properly. There is a jet up in the carb body, under the rubber plug. There are other jets inside the body under other jets/jet holders. Remove all jets, clean the cross-drilled air emulsion tubes, then check the floats for any pinholes that may cause them to sink. Synchronize both carbs exactly after you have each one set to an even idle speed and mixture setting.

Bill Silver