'93 yamaha virago 1100

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moldetch · #1 Unread post by **moldetch** » Wed Mar 28, 2007 11:36 am

need to know what i can do to help backfiring after the bike is warmed up, at idle or riding. my thought was a valve???

#2 Unread post by **Sev** » Wed Mar 28, 2007 2:12 pm

Backfiring is usually caused by unburned fuel detonating inside the exhaust system. This means you're not getting a clean burn inside the combustion chamber. First thing I would do is change the spark plugs.

When the exhaust it cool, shove a finger in there and feel around a bit, pull it out and check to see what color the "soot" is.

If it's black you're running rich and should get your carbs rejetted.
If it's a pale brown you're doing good.
If it's whitish you're running lean.

I think it's most likely that you're running rich and this is causing the backfiring.

If the valve was tight then it would always be open a little bit and you would have low compression. And a small amount of unburnt gasoline would be escaping into the exhaust and possibly backfiring. Have you had your valves adjusted recently? I think this is unlikely though.