Question about 1979 Yamaha XS 650 F
It would pay to check your HT lead on that cylinder and also check that after it has been misfiring, remove the sparkplug and see if it is wet and not dry that way you will be positive that it is the ignition system.
Apart from these couple of things it could be the coil playing up.
Let me know, if you need more information.
Posted on Aug 28, 2010
mixture or fuel regulating screw.The mix screws should come out. There's nothing holding them in once they're unscrewed all the way. They have a spring, washer, and o-ring on them that may be causing them to stick in the hole. If you cleaned the carbs using carb cleaner with the screws in place, that cleaner may have melted the o-rings. That could be what's holding the screws in. Unscrew them until you're sure the threads are disengaged then try grabbing them with some pliers and tugging them out.
You may not have gotten the passageway clear that these screws fit into and regulate fuel/air mix through. You really can't properly clean it with the screw in the way. That may be the cause of your misfire. Also, that little o-ring needs to be in there and in good shape for the screw to regulate flow properly.. Check fig:----
The 650 mix screw regulates the all ready made air/fuel mix that comes from the pilot jet. The strength of that mix can be altered by changing the pilot jet size on the BS38s. On the BS34s, it can be altered by changing the pilot jet size and/or the size of the air jet that feeds it.
The air/fuel mix from the pilot jet is delivered into the main bore through 4 tiny holes. 3 are clustered together about where the butterfly plate closes. These flow directly from the pilot jet and are unregulated. Whatever mix the jet sizes are producing will come out here. The 4th hole is off to the side (BS38) or ahead (BS34) of the 3 others and is the regulated feed from the mix screw. The mix screw gives you control and adjustment over approx. 25% of the feed from the pilot jet..Check fig:---
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Posted on Aug 28, 2010
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Posted on Jan 02, 2017
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