I recently posted about my 1980 Yamaha Champ (VERY similar to QT50 Yamahopper) and my problems starting/running.I received it recently after being dormant for 2 years. Did all of the cleaning and flushing and adjusting of fuel delivey, carburetor, and spark plug. Did not however drain and refil oil in tank (its injected) can this go bad too? Anyways after stumbling off of starting fluid and carb cleaner a number of times I found that clearing out the small idle jet did the trick and off I went!
This worked for about 3hrs of riding before sputtering out. I get it home (after LONG walk) to see what appeared to be a fouled plug (no spark) so after purchasing new ones and seeing spark on them prior to installing and attempting to start, it still would not even sputter at all. In fact after just a few kicks I would pull the plug to find it wet with gas and no longer seeing a spark when grounded. I repeated this process several times.
Then suddenly just as it did before, I put in yet another (about 5th) plug and it fired up first kick! Again ran for a couple hours and a good distance with normal engine and transmission behavior, running very strong with decent accelleration reaching 30-33 mph no problem, no excessive smoke, easy restaring after shutting off and just all out FUN! Then of course the same thing happened again! While going at a decent speed it sputtered out to nothing and would not restart even after changing to a fresh plug, I learned my lesson to carry an extra in my little basket. The plug that was merely a couple hours old looked good and clean, not overly dark and rich nor white and hot, just a good gray.
Now I am back to square one with it having gas, compression, air, and clear exhaust, and a visible SPARK before installing, yet, NOTHING! It is NOT the carburetor, it IS getting gas. I have researched and have read about a spark just not being strong enough and once the fuel hits it it is not strong enough to create combustion and is fouling out. Is this possible. It is CDI so no points to check for. Coil and spark plug wire are all one piece but I hear it is rarely the coil. Do either of these tend to fail? Why does it go so good when it goes, and then die out to NOTHING?! I am stumped. YES I have done all of Freds checklist to get it running, which is why I have it narrowed down to the ignition. I have been suggested everything from vapor lock (not it), to dirty points (dont have em), to broken flywheel key (what is it? do I have one with the CDI?) to bad plug (changed it 10 times) bad gas or mix (drained fuel several times, injection works) to bad coil/wire, to bad CDI box, to recently engine gets hot, head gasket changes shape thus losing compression, but this would not account for sparking issue after sitting a long time. But could I use a liquid high heat gasket in place of paper thin metal one? I am going crazy and have no clue! I just want to ride!