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1997 225HP Mercury outboard dies off after 10 min # 4000RPM

Gary Brown

New member
I have two 225 HP 1997 Mercury outboards, carbs. One will run 10 min @ 4000 RPM and then dies off slowly, then after rest for 15 min, will run again. Did that 5 times in a row in short succession. I have done the following: vacuum checked fuel lines including primer bulb back to tank; changed both fuel filters (canister and on top of carb); rebuilt the fuel pump, have 4 PSI @ carb @ idle; replaced the ignition switch; swapped ECM's, heat checked the crank position sensor and ignition coils; changed plugs; ohm checked the throttle position sensor; compression checked all 6 @ 135psi. Have not yet torn down the carbs. Runs in driveway for 1 hr no problems. Out of ideas, help!
 
Driveway running may point to fuel problems not ignition as ignition really doesn't know you are not under load but more fuel is required under load so that could be your smoking gun. Do you have priming squeeze bulbs on both engines? Are they fed from a common tank with Y fuel lines or something of the sort? When the engine dies, is the bulb sucked flat?

If the bulb is sucked flat on the failing engine yet soft and round on the good one it suggests that the failing engine is suffering from fuel starvation from the tank, aka restriction in the fuel line or tank vent not venting.

My 2c,
Mark
 
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