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Merc cruiser alpha one 5.0 backfire and won't open up after running 15 min

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searay123

Contributing Member
My engine runs for 15 min then acts up pops wont open up an eventually dies . I replaced dust cap rotor rebuilt carb replaced gas any help ?
 
Ayuh,.... Try runnin' it on a remote fuel tank fulla clean fresh gas, hooked directly to a fresh clean fuel filter, to the fuel pump,...

That'll eliminate the boat's fuel system from the equation,...
 
You'd be best to verify inadequate fuel pressure after the 15 minutes or so....and if the pressure drops when the lack of fuel issue occurs, its the fuel pump...if time is more important than cash, just change the fuel pump.
 
Damn straight! Just went through that with my outboard. You'd be surprised at the hell low fuel pressure can cause. You need at least 5 to 7 pounds pressure AT ALL TIMES for the carb to work properly.

Jeff
 
Seems I can duplicate on land get it up close to 170 temp then starts to fail or sputter open up it backfires . Takes a while to get warm enough to fail Erving and or running fine for a while
 
Ok read thru the posts...
When it happens and dies what is missing when you try to restart.
Spark? Fuel? What?
With out more diagnostics on your part there is no answer.
No easy button to push.

Just because the carb has been rebiult does not mean it is getting the right amount of fuel or good fuel.
Has the motor overheated?
One of the only ignition parts that typically shows heat related issues would be the coil.
Need more info and some additional diagnostics/trouble shooting results.
 
I didn't see a year or ignition type. The coil can act like it is failing on a TB ignition if the optic trigger under the rotor is failing. If the optic trigger is an old style the tiny wires on the bottom of it may be corroded and causing the problem as it heats up. Easy to check it by removing it and looking at it.
 
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