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L77JC4 or QL77JC4

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  • L77JC4 or QL77JC4

    I'm currently running my '76 85hp on L77JC4s as specified in the factory service manual. It runs great with them. However, I've read quite a few posts where the QL77JC4 seems to be the plug of choice for many CD ignition OMC V4s. In addition, I consulted my Champion manual and noticed that it specifically stated the "Q" designation indicates the plug is a resistor type for CD igntion systems. I know from experience electronic igntion modules are much more reliable when run with resistor plugs (and supression wires for that matter - but that's another discussion). Given this information, would I be better using the "Q" plug rather than the L77JC4 as suggested by the original manual?


  • #2
    Re: L77JC4 or QL77JC4

    web page

    And here is an up-to-date application chart site:
    [Edit]: http://continuouswave.com/whaler/ref...gChart2008.pdf

    Last edited by ezeke; June 7th, 2009, 07:28 PM.

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    • #3
      Re: L77JC4 or QL77JC4

      ezeke:Thanks for the link. According to this application guide 85hp motor from 1973 - 1980 can use L77JC4 or QL77JC4. So, I'm still a little perplexed, is one preferable over the other??

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      • #4
        Re: L77JC4 or QL77JC4

        Use the QL77JC4 plugs ...
        Rick

        "Boating is Life...All the rest is just Details"

        2007 Bentley 200 Cruise
        2007 Merc. 90 4 stroke

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        • #5
          Re: L77JC4 or QL77JC4

          www.sparkplugs.com

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          • #6
            Re: L77JC4 or QL77JC4

            I'm with Rick - use the "Q" plugs

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            • #7
              Re: L77JC4 or QL77JC4

              The Q plugs add a bit more resistance into the CCT. to suppress excess noice.

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              • #8
                Re: L77JC4 or QL77JC4

                Save the $$$, use the L77s. BTW, "Q" plugs are a suppressor type plug. They "suppress" RF noise, not to be confused with "resistor" plugs that provide "resistance" to RF noise. OMC went to Q plugs for two reasons. 1) an outboard running along (using non Q or R plugs) may cause interuption of, for example. actual radio transmissions from CBs, ship-to-shore, or single side band radios. Hense, the need to not interfer with crucial communications,ie; medical, police, etc.... small viliges in Alaska or Canada can appreciate not having your communications affected by some darm outboard running by! 2). OMC outboards in the mid 80's had a big-time problem with the VRO alarms going "off" when their was no apparent reason. Nuthing like zoom'n down the waterway and having horns, beeps and such making you and your favorite mechanic crazy trying to find out why!!! OMC must of spent billions on replacement VROs due to this problem. A method of reducing RF noise was needed. "Let's "suppress" that stuff!!" And 3) 60 degree OMC motors with OIS (Optical Ignition System) MUST run Q plugs!!!! That system does not like any more "resistance" in the system!! So, again, let's "suppress" RF with Q plugs. I've seen starter motors and blocks break due to uneven ignition and a motor miss-fire. Many motors are not affected by RF,and as such there may not be a big advantage to running them. A 1976 85 hp dosn't need Q plugs but they won't hurt if you do run them!

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                • #9
                  Re: L77JC4 or QL77JC4

                  This is what Champion has to say about their plugs and I'd go with it...
                  ResistorAt the moment the spark jumps the gap it causes a high frequency burst of energy, this is known as RFI (radio frequency interference). This is why Champion introduced resistor spark plugs in the mid 1960's. Placing a resistor within the spark plug suppresses the RFI . Without resistor plugs in your car you can experience static on your radio as well as interfere with other sensitive electronic equipment. Some later model vehicles as well as newer Powersport engines must use resistor plugs for a proper "talkback" to the electronic ignition. Outboard marine Capacitive Discharge Ignition (CDI) such as used on some Johnson and Evinrude marine engines require a special inductive type resistor ( such as a Champion Q-type resistor ). Use of non-inductive resistor type plugs on these motors can cause misfire and poor performance.For automotive CDI high output ignition systems systems (such as Mallory, MSD, Crane and Accel), refer to Resistor plugs for race engines for information relative to modified motors.
                  Rick

                  "Boating is Life...All the rest is just Details"

                  2007 Bentley 200 Cruise
                  2007 Merc. 90 4 stroke

                  Comment



                  • #10
                    Re: L77JC4 or QL77JC4

                    For what it's worth, my dealer told me there was no reason to pay the extra $2 bucks a plug for the Q on my '79 v4 115hp. He said all it did was suppress radio interference. I took his advice.

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                    • #11
                      Re: L77JC4 or QL77JC4

                      Geez, I only pay $2.00 or so at Walmart for the "Q" plugs anyway. $6.00 a year ain't bad...
                      Rick

                      "Boating is Life...All the rest is just Details"

                      2007 Bentley 200 Cruise
                      2007 Merc. 90 4 stroke

                      Comment



                      • #12
                        Re: L77JC4 or QL77JC4

                        I've got what it appears to be a mid 70's 70hp Evinrude. Before oil injection or fuel injection. Im not sure which to use, L77JC4 or QL77JC4.

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                        • #13
                          Re: L77JC4 or QL77JC4

                          Go with the Q. I remember back when automotive engines became controlled by computers and it was (and is) a requirement to suppress the interference. Drove me batty figuring out the early "check engine" lights.

                          But then I wised up, left the trade and got married (yes, that WAS an oxymoron)

                          24 years later, I'm happier than ever before. The only thing I have in tow is my BOAT!!!!

                          Comment



                          • #14
                            Re: L77JC4 or QL77JC4

                            The difference between "L" series plugs and "QL" series plugs is that QL ones have a low resistance, inductive suppressor The "L" ones are not suppressed at all.

                            You must not use ordinary resistor suppressed plugs with the OMC CDI system ie those beginning with an "R"

                            ( the equivalent in NGK plugs are denoted by a "Z" in the number .... Do not use plugs with an "R" in the number)

                            For a good detailed, technical explanation, better than the explanation on Champions own site see

                            http://members.iinet.net.au/~pauldaw...park-plugs.PDF

                            "QL" plugs are recommended for all engines with VRO/OMS systems for the reasons already given

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