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Unread 03-21-2013, 10:19 PM
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Smithers Smithers is offline
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Location: San Luis Obispo, CA
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#3 SPARK

Just for the heck of it we decided to check the spark. And boy did we get some spark. With the sparkplug dangling about an inch away from the exhaust header we could see huge spark connecting between the two. Then when we held the plug right on the header we got a flash of white spark. To most people that means they have spark. To me that just seemed like an odd spark. It was too much spark. You might think of it as a wreckless and uncontrolled spark. The resistor was not working properly. While inspecting the spark plug boot I could see obvious signs of overheating. The boot actually stuck to the spark plug like it had melted so I knew right off the bat before I bought the bike that there was more to this bike than what you could see on the surface. When I came back with a new plug the spark was not as explosive but it was a controlled violet colored spark.

The bike fired right up. I was very happy but not out of the woods just yet. The engine would die as soon as you pushed the choke in and I had to adjust the idle screw very high to get the bike to hold idle. Then when I would back off the engine would die. At this point it wasn't easy to start anymore and it surely wouldn't hold a proper low rpm idle speed. Not even close. Something was wrong with the carb but I just spent all sorts of time going through the carb and checking for proper flow in all the passageways and everything.

What was the last thing on the whole bike that I didn't check? The fuel screw! I knew I would find something wrong. The fuel screw controls a lot of the mixture throughout the whole rpm range and it also has a lot to do with starting. I had backed it out 2 turns to begin with but there was a deeper problem. I removed the screw and it simply dropped out of the hole. There wasn't a spring, washer or o-ring to seal off the outside atmosphere from entering in around the screw into the fuel stream. If you don't put the o-ring and the other washer and spring that holds the o-ring tight against the fuel screw you won't have a chance to get the bike to run correctly. The added air simply leans out the fuel mixture and causes a massive lean condition. This is why the bike would only run with the choke on! The mixture was so lean that the choke counteracted this by flooding the carb! What a way to ride a bike!!

And now you know why the spark plug boot was melted to the damaged spark plug. Overheating was the result. Kinda funny how the chain of event unfolds. When you have a condition in any engine you have to ask yourself what was the root cause of this change? You will always find a reason why you have the obvious problem in the first place.
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