Those automatic compression releases can be a real pain! If you aren't familiar with them, they are built into the cam lobe that operates the exhaust valve.
The ACR consist of a spring-loaded arm that, when the engine is turning below a certain RPM, causes a sort of D-shaped "bump" to rotate proud of the exhaust cam lobe surface, but only when the engine is coming up on the compression stroke. So at lower RPM's the "bump" contacts the exhaust cam follower and bumps the exhaust valve open.
When the engine is rotating over that given RPM, such as when the starter motor really gets the engine cranking, the centrifugal force causes the arm to swing outwards, and the "bump" rotates to be flush with the cam. The exhaust valve remains closed on the compression stroke, allowing the engine to start and run.
If your battery is weak, it may not get the engine spinning fast enough to defeat the ACR, so the exhaust valve opens on each compression stroke and the engine never starts.
I put a pretty high cranking amp battery in my Frankentractor (1000 with a 1200 engine), and that baby starts almost immediately when you turn the key! Putting in a higher-than-stock cranking-amp-capacity battery does no harm to the starting circuit, as the starter motor will only draw the amps that it needs. But if the battery can't deliver the amps, then the starter motor is sort of choked off.
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