Motorcycle Repair: Maintenance/Repair, air oil, valve timing

Question
Falcon-
I just bought a 1983 yamaha viraago xv700 with 12K.  i took it in for carb cleaning, and the air & oil filters were changed as well.  The old problems are still there:  sputtering, coughing, backfire, power is low then comes through in bursts while riding.  Typically a bigger backfire will open things up and the bike will ride normally until i stop riding.  it doesn't always happen, and never reverts in the middle of a ride once it's clear.  of course, when i took it back to the shop, it was running perfectly.  they told me to bring it back when it acts up, but the last couple of times it's cleared up on the way to the shop.  can you tell me what you think is happening and if i need to take the bike back in or if a home quick-fix is possible.
is this still carb-related, or spark plugs?
thanks for your help.


Answer
Hi Phu.
 Here are some things to check;

1)  Carb synch.  If the synch is off, the timing will be off.  The XV series is set up so that synchronizing the carbs will reset the timing.  Do this before you do valve ajustment.

2)  Valve timing and adjustment.

3)  Carbs.  Are they clean or do they need cleaning?

4)  Air filter.  Is it dirty or due/overdue for replacement? This is something that Yamaha's a re notorious for and unless they are really used to dealing with Yamaha, then most shops won't know to check this as relates to engine operation.

5)  Ignition system.  Any shorts, bad/dirty connections or bad components?  Search and repair/replace.

6)  Fuse and fuse connections for the ignition system.  These could cause symptoms like you describe if the fuse is marginal or the connections are bad/dirty.

Start with those and let me know what you find.
Good luck.
FALCON