Maritime
Over 10,000 Posts
If you are blasting it into the intake with motor running, it will get blown out of the exhaust. Seafoam does the same thing. If you are taking the plug out and filling the cylinder and letting it sit, you can then take the plugs out of all cylinders and turn the motor over to blast the cleaner out as well. Try it running, then the one bad one spray a bunch in the spark hole and leave it overnight, then in the morning leave the plug out, take the plugs out of the rest and spin the motor. put a rag over the one hole that had cleaner so it doesn't fly all over. Once it is all sprayed out, put plugs back and run the motor again till warm then test compression.