I have an 82' 50 hp, 4 cyl 2 stroke. I've always had low rpm random misfires while cruising slowly in gear. It's kind of annoying. The plugs usually look fine aside from one black spot on the ceramic of each plug. But they don't ever foul out. It's been having a little less power the last few years even though compression is all in the 130-135 range.
My question is regarding what the exact proper spark plugs should be that Mercury intended to have in there. The mercury book says L78V Champion. Champion claims that's a non-resistor plug. Last time I changed them, they weren't available so I bought NGK BUHW-2 (which are definitely non-resistor). It seems like it's always run a little rougher now at low rpm. NGK tech support says I have to run their BUZHW-2 plugs which are resistor type- and they claim that the original Champion plugs were also resistor type. Their tech support guy said using non-resistor plugs on my engine will cause problems in the ignition coils and cause random misfires, because they're very sensitive to the line noise caused by the non-resistor plugs.
So, besides stories about who uses brand X plugs and how good they supposedly worked, does anyone really know the stock ignition system on my engine and what kind of plugs (AND WIRES) I really should be using?
Also- last year I changed the wires with a brand new set costing about $45 at we$$$ Marine... and it ran horrible. I ran it at night with the cover off and saw every wire was throwing huge crazy sparks everywhere to the case of the engine, right through the wire shielding. I saw that the original 1982 dated wires that were on it, were solid core, and the we$ ma$ine wires were resistor core. So for $8 worth of wire and caps, and ends, I made my own set from Napa. Those new home made solid core wires don't throw any sparks to the crank case, and it was a major difference in low rpm quality.
So what does this mean as far as using the correct resistor or non-resistor plugs??
JOE
My question is regarding what the exact proper spark plugs should be that Mercury intended to have in there. The mercury book says L78V Champion. Champion claims that's a non-resistor plug. Last time I changed them, they weren't available so I bought NGK BUHW-2 (which are definitely non-resistor). It seems like it's always run a little rougher now at low rpm. NGK tech support says I have to run their BUZHW-2 plugs which are resistor type- and they claim that the original Champion plugs were also resistor type. Their tech support guy said using non-resistor plugs on my engine will cause problems in the ignition coils and cause random misfires, because they're very sensitive to the line noise caused by the non-resistor plugs.
So, besides stories about who uses brand X plugs and how good they supposedly worked, does anyone really know the stock ignition system on my engine and what kind of plugs (AND WIRES) I really should be using?
Also- last year I changed the wires with a brand new set costing about $45 at we$$$ Marine... and it ran horrible. I ran it at night with the cover off and saw every wire was throwing huge crazy sparks everywhere to the case of the engine, right through the wire shielding. I saw that the original 1982 dated wires that were on it, were solid core, and the we$ ma$ine wires were resistor core. So for $8 worth of wire and caps, and ends, I made my own set from Napa. Those new home made solid core wires don't throw any sparks to the crank case, and it was a major difference in low rpm quality.
So what does this mean as far as using the correct resistor or non-resistor plugs??
JOE
