:eam Annnnd....that will do what???????
even when the throtle is closed the buterfly is slightly open to allow sufficient fuel/air mixture into the engine to run but any restriction in the incomming airflow will affect the compression test
to get a correct reading you need to give the best air flow possible to eliminate any inaccuracy
Brian
I always did compression tests by bumping the starter. Never with the engine running.
Open or closed throttle won't make any difference.
It makes a very noticable difference in the numbers. The throttle plate should always be open for the truest reading of the compression. In a CV carb the slide should be held up too.
How does an engine start at all if the cylinder(s) won't fill with air/fuel?There shouldn't be more than a 10% difference between cylinders but the compression numbers is what determined the internal condition of the cylinder rings/valves etc.. With the carb butterfly closed the numbers aren't true compression numbers and will always be lower than the actual compression which is being done to ascertain the actual condition.