Small Engines (Lawn Mowers, etc.): B&S 20hp / Electrical problem, headlight wiring harness, compression release

Question
Mower: MTD Yard Machine model 675
Engine data: B&S Model 461707 Type 0141 E1    Twin II 20hp

The engine is not getting full power to the starter. Metered it's around 8 volts. When I turn the key the flywheel turns approx one turn and I hear a whine from the solenoid. When I pull the spark plugs the starter motor will turn the engine. It seems when there is compression the starter is not getting enough power to turn the engine. So far I have replaced and done everything except pull the wire harness apart. I have replaced the battery, starter and the solenoid. I have checked the wiring for breaks and continuity. I have checked both deck safety switches. The seat switch only activates when the deck is lowered and engaged so I haven't spent any time tracing it. The key switch meters properly across the terminals when checked. I have disconnected the headlight wiring harness in case it is shorting. I have jumped the starter motor directly to the battery and get the same response from the starter. The battery has 12.4 volts when metered.

This thing has got me pulling my hair out, well, at least what I have left. What could cause no power to the starter, and the same response from the starter when jumped? The starter and solenoid are brand new?

Here is the link to the engine parts schematic: http://shop.briggsandstratton.com/BShopProductPage.asp?CatalogID=56B2B9A7-283C-1...
(click on "view PDF")


Answer
Hi Dan,

Your question would have had me clueless, especially since you have replaced all the major components but a recent question may hold the answer.  There a may be a compression release on your engine that is malfunctioning.  I am not familiar with this, though.  Does it not crank with the plugs installed but the wires disconnected?

Michael