mercury 40hp 1983 wont run under a load? HELP PLEASE???

[lazzlonewolf]

I got a 83 MERCURY 40HP. IV TRIED EVERYTHING TO FIX THIS MOTOR. I REPLACED ALL THE WIRES NEW STATOR NEW STARTER REBUILT CARB NEW SPARK PLUGS. IT RUNS FINE ON LAND CAN PUT IT IN GEAR AND REV IT FULL THROTTLE AND IT DONT MISS A LICK. PUT IT IN THE WATER SHIFT IT IN GEAR AND IT WILL RUN REAL SLOW, GIVE IT SOME GAS AND IT STALLS. WHAT THE HELL IS WRONG WITH IT????? I CANT FIGURE IT OUT???

 

[CharlieB]

Re: mercury 40hp 1983 wont run under a load? HELP PLEASE???

Either one cyl not firing or the carbs are dirty/misadjusted.

Test spark and compression to rule out ignition and mechanical problems.

Clean and adjust carbs to ensure correct fuel flow. A lean carb will rev freely while on the hose and in Neutral once in the water but bog and die once under load.

 

[Jeff Lindquist]

Re: mercury 40hp 1983 wont run under a load? HELP PLEASE???

that is exactly the issues i am having with a 1982 80hp 4 cylinder mariner. i will be testing this weekend after rewiring the 8 wires from the switchbox to the coils (very crumbly from running right alongside block i presume). rebuilt carbs, new plugs, used same sparkplug wires but ENSURED they are making contact in the coils before sliding boots over top (very tight area behind throttle and spark arms). removed mercury switch and ordered new solenoid that went after cranking it over in the water forever. i will test the rectifier last once the solenoid gets here.
my symptoms were a decent idle, bogging out in the midrange unless very warm after a good rip, and full throttle fine.

 

[lazzlonewolf]

Re: mercury 40hp 1983 wont run under a load? HELP PLEASE???

Either one cyl not firing or the carbs are dirty/misadjusted.

Test spark and compression to rule out ignition and mechanical problems.

Clean and adjust carbs to ensure correct fuel flow. A lean carb will rev freely while on the hose and in Neutral once in the water but bog and die once under load.

both cyc firing. good spark i did a compression check and both cyc are reading only 50psi is that to low? and how do i get better compression?

 

[CharlieB]

Re: mercury 40hp 1983 wont run under a load? HELP PLEASE???

If a motor starts and runs and a compression tester shows that the cyls are even, but only 50 psi, I bet money that the gauge reads low. Don't worry about it, as long as they are even and the motor starts the compression is not your issue.

Clean the carbs, test fuel pump flow while cranking, adjust the carb linkage and motor timing per the factory service manual.

 

[82trophybass]

Re: mercury 40hp 1983 wont run under a load? HELP PLEASE???

I'm having a similar problem did you ever figure it out?

 

[Rollercoaster]

Re: mercury 40hp 1983 wont run under a load? HELP PLEASE???

bad reed block!