Motorcycle, 94 Yamaha Virago 750 two cylinder. As I'm driving down the highway I pull the spark plug wire off of the front cylinder and nothing changes in performance. But when I pull the spark plug off of the rear cylinder, the engine dies.
Air, Spark, Carbs (fuel), valve adjustments, are all good. The front cylinder has compression of 90, rear has compression of 120.
Exhaust patch work from previous owner (made with kevilar) failed/burnt out 1 month ago leaving a hole in the header. Last oil change I saw the oil viscosity was like water, and the color was charcoal.
After patching the exhaust, the non-firing (front) cylinder, it's is now blowing black smoke, but only when the throttle is open all the way. There is still no improvement in performance.
It still drives as if the front (90 compression) cylinder is NOT firing at all, aka the bike still has the same power as if only one of the two cylinders is firing.
Again, air, spark, (and carbs) valve adjustments, are good. compression is decent (90 on front - 120 on rear)
Oh yah, and the brand new spark plug on the front cylinder (that aint working) is blobbed with oily deposits after 5 minutes of running.
I think that the header hole caused the exhause to fill into the front cylinder.