Good evening!
I've got a Mercury Classic 50 that came on a 17' Corson Fiberglass runabout that I picked up earlier this summer. When I got it, the motor wasn't running. Previous owner replaced the plugs, wires, and switchbox, and rebuilt the carbs. I replaced the Stator and Trigger, and it worked fine after that. I used it for about a month, probably with a total of 15 hours of run time. Gradually I noticed that my WOT RPMS were dropping, from around 5500 at WOT originally to a new max of around 4800 RPM's. Around the same time it developed an intermittent skip at WOTaround , and a consistent skip at mid-throttle. I did some research online and thought it may need a decarb, so I did that and swapped out the plugs for a fresh set afterwards. No difference.
In the last month while trying to diagnose this issue, I have done the following:
ELECTRICAL:
*ohm'd the coils and replaced two that read very slightly on the low (but still within spec) side. No change
*played switcharoo with every combination of all 6 of the coils on hand when that didn't make a difference. No change
*swapped the spark plugs around, with every combination of the 8 plugs on hand. No change
FUEL (after some repair threads suggested the possibility of fuel starvation):
*Rebuilt fuel pump. No change
*Replaced fuel filter (also tried deleting it altogether) No change.
*Replaced fuel bulb. No change
*Replaced all fuel lines. No change
*Cleaned and rebuilt carbs with new needles. No change.
*Tried running straight from a 5 gallon can to rule out a problem with my tank. No change
I also have messed with the fuel mix, the throttle linkage settings, retarded and advanced the timing, and thrown a temper tantrum.
Compression is good, all 4 cylinders read between 140-150. Spark is strong at idle (where I have been able to test it, since I'm working alone) and will jump a 1/2 gap without any problems.
I'm stumped. Can anybody point me in the right direction before I cave and take it to the local marina? I REALLY don't want to pay their labor rates.
I've got a Mercury Classic 50 that came on a 17' Corson Fiberglass runabout that I picked up earlier this summer. When I got it, the motor wasn't running. Previous owner replaced the plugs, wires, and switchbox, and rebuilt the carbs. I replaced the Stator and Trigger, and it worked fine after that. I used it for about a month, probably with a total of 15 hours of run time. Gradually I noticed that my WOT RPMS were dropping, from around 5500 at WOT originally to a new max of around 4800 RPM's. Around the same time it developed an intermittent skip at WOTaround , and a consistent skip at mid-throttle. I did some research online and thought it may need a decarb, so I did that and swapped out the plugs for a fresh set afterwards. No difference.
In the last month while trying to diagnose this issue, I have done the following:
ELECTRICAL:
*ohm'd the coils and replaced two that read very slightly on the low (but still within spec) side. No change
*played switcharoo with every combination of all 6 of the coils on hand when that didn't make a difference. No change
*swapped the spark plugs around, with every combination of the 8 plugs on hand. No change
FUEL (after some repair threads suggested the possibility of fuel starvation):
*Rebuilt fuel pump. No change
*Replaced fuel filter (also tried deleting it altogether) No change.
*Replaced fuel bulb. No change
*Replaced all fuel lines. No change
*Cleaned and rebuilt carbs with new needles. No change.
*Tried running straight from a 5 gallon can to rule out a problem with my tank. No change
I also have messed with the fuel mix, the throttle linkage settings, retarded and advanced the timing, and thrown a temper tantrum.
Compression is good, all 4 cylinders read between 140-150. Spark is strong at idle (where I have been able to test it, since I'm working alone) and will jump a 1/2 gap without any problems.
I'm stumped. Can anybody point me in the right direction before I cave and take it to the local marina? I REALLY don't want to pay their labor rates.
