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Old 09-28-2020, 01:28 PM
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Gas engines make about 10-12hp for every gph they burn. Two strokes a bit worse, four strokes a bit better. This only applies to mid-upper power settings. At low power or near idle the burn rate per hp is much worse. Diesels are 16-20hp per gph.

To the OP's question, with a 15hp at cruise power (not full power) expect 1-1.5 gph.