25hp mercury losses power after running 30 minutes

[hunt4life69]

i have a 25 mercury 92 model that will run fine at first , but after about 20 to 30 minutes the motor will bog down still idols fine but it seems to load up it starts out getting slower and slower till all you have is a idol.

 

[ONERCBOATER]

Re: 25hp mercury losses power after running 30 minutes

gas can vent open???? should be.
how hot is engine getting? could by just no quite enough cooling water,
fuel filter?????

my guess is fuel delivery issue....but...... just to be safe... test spark when it does this behavior and see if you lost spark on one cyl.... smaller engines run ridiculously well with one cylinder down. coils can get stupid as they warm up and be faulty hot but not cold.

also what do your plugs look like right after it quits like this?



Sean

 

[hunt4life69]

Re: 25hp mercury losses power after running 30 minutes

i guess i should have mentioned i have replaced the fuel tank ,hose,bulb,and cleaned carb, checked coils,swaped the ignition out with one off a working motor and still the same problem, i been thinking fuel pump but it just doesnt seem posible , looks like it would do this from first start up not after running the motor and the problem gets worse the more you run it it sarts out from full throttle down to 3/4ths down to 1/2 , to only a idol and will idol all day long .