I need help

[Stan9867]

Hello again
Last year I had trouble with a 70 hp 3 cyl mercury outboard. One of the pistons the top one had its rings held in the grooves by what looked to be the raised part of the piston which had gone comepletly to pieces. I rebuilt the motor 3 new pistons,impeller,and new gasket kit. Engine worked fine for about 6 hours. The top cylinder cut out, plug was fouled by bits of alluminum. This looks like a repeat of last year.I have replaced the impeller, used double the amount of oil in breakin period, made oil gas mixture richer, Could not check timing but motor seems right no binding while starting and runs good. Any advice would be greatly appreciated. I am afraid the same thing is happening again.
Thank you
Stan

 

[Fuzzytbay]

Re: I need help

Sounds like pre detination in the cylinder. If not, its running too lean. Wrong oil/gas mixtures, can cause leaning, so don't ritchen up the mixture to much. Second, run 91, or better octane gas. Third, get that timing checked, much cheaper than rebuilding a motor. Fourth, check out the carbs/fuel system, and check for leaning conditions, ie dirty or miss adjusted carbs, air leaks in the fuel lines/fuel pumps. Also make sure the water pump is working, top cylinders are the first to go, on overheating.

 

[Stan9867]

Re: I need help

Thanks for quick reply. I will check timing. What bothers me is why one cylinder and whyb the same one. Could a coil be putting out to much or something that just affects that one cylinder?
Thanks again
Stan

 

[CharlieB]

Re: I need help

Either a weak fuel pump, fuel line restriction, or air leaking into the fuel line, any one or all reduce the volume and fuel pressure enough that the top carb is NOT kept filled at WOT, causing it to lean out #1 cyl and start melting that piston.

Make double sure that ALL fuel lines are good, all fittings tight, rebuild the pump and re-clean all carbs before attempting to run this motor again.