I just discovered this last night, and haven't had a chance to troubleshoot yet. Figured some of you might enjoy pondering it too.

I just figured out why my fresh 225 runs like garbage, and I can't get it dialed in. When the engine is not under load, I lose all spark. Give it some throttle, there is spark. Let off the throttle, there is none.

I have a spare ECM, and possibly another coil I hope to try this weekend, as well as tracing some wiring...

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Is the engine well grounded to the chassis?

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Joshua

It could be the wires inside the distributor,going to the pick-up coil.the coil moves to cause changes in vacuum advance.

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V8?? We don't need no stink'n V8!!

Could be the bushings in the distributor are shot causing the air gap on the pickup to change. I had that happen to me on my 84 Ford van. Swapped the guts of the old distributor into a remanned dist housing and everything worked fine.