Motorcycle Repair: Motorcycle wont start and backfires, air fuel mixture, yamaha 175

Question
During a trail ride my 1975 Yamaha 175 suddenly cut out as though out of gas.  I couldn't kick start it after that and only got it started by coasting downhill and popping the clutch.  Now it won't start at all.  I checked the fuel flow which was OK.  Also, when attempting to push start it backfires.

What's going on?

Answer
Hi Bill,

Remove the spark plug and inspect it for evidence of fouling.

Visit "www.ngk.com/sparkplug411.asp" click the link "Problem Plugs" on the left menu. Compare your plug with the images on the website.

The matching image may explain why the engine will not start and run.

Otherwise, the engine needs correct air/fuel mixture, a spark at the exact time, and adequate cylinder compression to run.

You'll have to troubleshoot each element until the cause of the problem is known.

I suspect a ignition problem.

Respectfully,
Mark Shively