Motorcycle Repair: Virago 920 carbs, bikebandit com, vacuum type

Question
I have a 1983 920 Yamaha Virago.  Over the years I have had carb sync problems. This year I have a new problem.  The front cylinder seems to go dead.  Not sure if its a lack of fire or fuel.  Plug is very clean as though no fuel.  This occurs at low RPM. Above 5000 PRM the front cylinder kicks in.  Can you explain what the mixture control valve does.  It has two vacum lines both going to the front cylinder.  Any help would be great.  I'm running out of ideas.  Also can you tell me if there is any other vacum gauge, other than a mercury, that can be used to sync the carbs?  

Answer
Hi Mark,

I'm referring you to the following website links for answers to your questions. Visit "www.yamaha-motors.com" and "www.bikebandit.com" to see microfiche parts views on line.

www.vroc.org/dbva/php/faqdisplay.php3?category=mods#question5

www.viragoownersclub.org/all_link03.htm

www.viragotech.com


For air vacuum type synchronizing tool visit this link. Look on Ebay for same product at better prices.

www.jcwhitney.com/autoparts/ProductDisplay/s-10101/storeId-10101/p-3990/c-10101/catalogId-10101

Keep me posted on your progress.

Respectfully,
Mark Shively