dollar bill trick?

[firechero]

ive seen people put a dollar bill up to the exhaust before to see if the exhaust sucks in, whats the point of this? my uneducated guess is maybe intake leak?

[carrotman]

First you use a twenty. Second you borrow the twenty from somebody in the audience. Third you palm the twenty and say it was sucked up the exhaust.

[Rogue]

checking for burnt valves - not a "true" test but can be a good indicator - only prob is a small misfire can cause same reaction and as you may know a misfire can be caused by fuel, spark, or say a burnt valve