Preigniting???

[CRobL]

Hello all, nice forum you have here
I'm currently *trying* to repair my '85 Yamaha Virago XV700 and have just adjusted the fuel levels. The levels are about 2-3 millimeters from the top of the float bowl.

But I don't think that's my problem. My problem is that when I start my bike and idle it, I get a popping sound and as it pops, carb #2 looks like it's getting punched from the cylinder becuase it physically 'bounces' out for a split second.

It would seem to me that it's preigniting too close to the carb and thus popping the carb a little as it fires. This is on choke or off.

BTW, and this is probably important,,,,it seems like I'm running on only one cylinder becuase I have almost no power.

p.s. The plugs both get carbon fouled every time I've run it. I know becuase each time I take them out, I clean off the end (terminal).

[BuzZz]

You could have a tight(mis-adjusted) or possible burned valve....

[CRobL]

Fortunately, that's not the problem (yet, anyway). Hopefully I can avoid adjusting valve clearances on this bike.

Anyway, I've found out what is possibly my main problem. The petcock is intermittently working, and then not working, in the 'on' position. I've sucked on the vacuum line and fuel came out, ten minutes later, after a hard ride, I sucked on the vacuum line again and no fuel came out.

This would explain my fuel level problems in my float bowls after running it with the petcock in the 'on' position.