I'm trying to get a 71 cb350 to run and I'm having trouble getting it to fire on the left side. The plug sparks when out of the engine, and a timing light shows that it's sparking when its running, but the exhaust is cold and when I pull the plug, it's still looks new. There is definitely gas getting to the cylinders. It's got a new points plate and points, and the carbs have been cleaned. I'm sure the carbs need adjusting, but I can't get it to run well enough to so. How much spark is enough? Could it be just that the spark is too weak?