90 johnson 90HP VRO Spark Plugs

[ralphjg]

I know this has probably been answered 100 times but I had been using Champions L77JC4 gapped at .035 but when I picked up other new parts with a set of plugs dealer told me QL77J4C gapped at .030.Put in new plugs and didn't seem to have as much power.<br />Thanks in advance

 

[Joe Reeves]

Re: 90 johnson 90HP VRO Spark Plugs

Ralph.... The "Q" simply indicates that the plug is a "Suppressor" type plug which helps quiet electrical interference (noise) in electronic and electrical components.<br /><br />That year engine calls for a .040 gap (trust me).

 

[Jack Shellac]

Re: 90 johnson 90HP VRO Spark Plugs

I'm looking at the OMC manual for that motor and it calls for QL77JC4 gapped at .030". I wouldn't dare question Joe Reeves expertise but wonder why you recommend .040", Joe??? Is this also true for the 1990 88 SPCL?

 

[Joe Reeves]

Re: 90 johnson 90HP VRO Spark Plugs

The Magnetor Capacitance Discharge ignition systems which came into being in 1973 have used the .040 gap right up through the years until some point.... apparently 1990 if that's what your manual states, and this .040 has proven to be what what was needed.<br /><br />Why the gap was changed to .030 I have no idea but it has caused some confusion. Boaters with the older engines have used the .030 gap and that has caused ignition intermitent problems, various problems, that when the gap was changed back to .040.... those problems vanished.<br /><br />Many of the newer engines (1990 up) have also met with problems using that .030 gap (not all), but when the gap was enlarged to .040, those problems vanished.<br /><br />Bottom line.... if .030 works for you, fine. If any kind of problem exists (idle, high speed breakup, etc), try the .040.... worth a try.

 

[seahorse5]

Re: 90 johnson 90HP VRO Spark Plugs

The factory recommendation was changed from .040 gap to .030 gap quite a few years ago. On some motors, the VRO would pick up the radio frequency interference (RFI) when the plug gap approached .045 or so. So starting at .030" leaves a lot of room for wear, especially on those motors that went more than 100 hours on plugs. The plug gap grows about .010" in 100 hours of normal use.<br /><br />On the V4's from 1979 on up, the factory plug is also QL82C which gives a better life at low speeds with less fouling than the QL77JC4 plugs. For the past few years, the QL82C is standard equipment on those crossflow motors.

 

[Jack Shellac]

Re: 90 johnson 90HP VRO Spark Plugs

Thanks, Joe. Your knowledge and expertise is always greatly appreciated.