Hi,
For four stroke the piston is at TDC either when the spark is lit and you have the power stroke. Both intake and exhaust valves are closed and you can't blow into the hose.
0r when the piston is returning to TDC again, the last of the exhaust is being pushed out and the exhaust valve is almost closed and for more performance cams, the intake valves are also just cracked open before TDC. When in this position you can blow into the hose.
Quote:
Originally Posted by 40 Deluxe
No, if you can blow in the hose, you are on either intake stroke or exhaust stroke. Both valves are closed on both the compression and power strokes.
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