Motorcycle Repair: Running on one cylinder, vacuum hoses, cb400a

Question
I have an old 1978 Honda CB400A (Hondamatic) that I am trying to get running. The engine has good compression on both cylinders (120 psi) and I have spark in both plugs. The carbs have been complete cleaned. I can get the bike running and there is good pressure and heat coming out of the left side exhaust but very little on the right side. If I put my hand over the right carb throat to cut air flow down the right side comes alive, it back fires some but runs better, as soon as I take my hand away it goes back to were it was. My first thought was a carb problem so I had another set of carbs, they were complete gone thru and cleaned, installed and the exact same thing happened. There is more suction coming from the carb on the right, again if you block some of that flow the engine idle speeds up and the pressure out the exhaust equals out to the left side. Do you have any ideas? Could I have a weak spark on the right and it is not igniting the gas? I have tired new plugs, adjusting the carbs, etc. but can't seem to get it running right, I am running out of ideas. Please help if you can.

Thanks.

Brad";  

Answer
Hi Brad,

I suspect the carbs need adjusted.

Ensure valve clearances are properly adjusted, then synchronize the carburetors.

Is the airbox and air ducts free of objects such as bee and mice nests? Is the air filter clean and in good condition?

Are the throttle slides working properly?

Check fuel and vacuum hoses. Vacuum hoses may collaspe when worn. Is the petcock cleaning and allowing fuel to flow and fill both float bowls?

You may have a weak ignition on the right side. Grounding a spark plug to the engine and watching the pretty arc verifies the plug arcs. Under compression, a plug may not produce an arc.

Respectfully,
Mark Shively