Motorcycle Repair: I think my 1977 Yamaha Enduro DT100 is dead, piston rings, dt100

Question
Hi Chris-
I resently aquired a 1977 Yamaha Enduro DT100 from a friend who left it to rot in a barn for the last 5 years or so (according to him, it was running 5 years ago). It is my first bike and so please bare with me. I've replaced the battery, checked the spark plug, checked the wiring and refilled the fluids. All seems OK. Everything is turned on that should be on. I hold down the clutch, put it in neutral and hit the kick start but the motor still refuses to start. What else can I check?   

Thanks, Lynne

Answer
Hi Lynne.
 Did you clean the carb out?  I mean a proper, disassembly cleaning.

This becomes a common problem with bikes that have spent too long in storage without being properly set up for it.
What happens is that the fuel that is left in the system evaporates, leaving a nice, gooey residue that we have come to call "Varnish"  (It looks like varnish, thus the name).

It contaminates the entire fuel system and will prevent the carbs from working right, and sometimes it will prevent the carbs from working at all.  Clean out the carb completely and properly.

Another thing to check is to see if you are getting spark.  This is one of the simplest tests to do.
Get some automotive starting fluid and spray it into the air intake immediately prior to starting the bike.

If you have spark and compression then it should start and then die.
If you have spark, compression and fuel flow, it should start and run.
If you have spark, compression and varnished carbs, then it should start, maybe run, maybe not.

Even if you have spark without compression, it should fire, but will not do any more than that.

You can get a compression testor and see if you have compression.  Match what you find against the specs in the repair manual.  If those readings do not match the minimum specs or better, then you need to work on the piston, rings and cylinder head internals.  They could all be damaged if that is the case.

Even with all of that, I still feel, in your case that it is a case of a gummed up carb and possibly no or low spark.

One last thing that I almost forgot.  Make sure that your ignition timing is right and the valve gaps are set correctly.  Without those things being right, it will never run.

Check those out and let me know what you find.
Good luck.
FALCON