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QL77JC4L77JC4 Spark plugs

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paulholcomb

Regular Contributor
"I've been researching the

"I've been researching these plugs and behold...... I found a plug that my owner's manual calls for. The UL-77V. According to Champions website its a racing application plug. It has no adjustment....it's missing the electrode at the bottom of the plug. Joe or Graham......or someone that thinks you're in the same league.....what's the pros and cons for switching to the plugs you're telling everyone to use compared to these racing plugs my owner's manual calls for? I have purchased 3 of each...3 (QL77JC4), 3 (L77JC4), and 3 (UL-77V). I'm leaving for Nebraska to Lake McConaguay on Thursday, 12 July, and will be coming home, Thursday, 19 July. I will let everyone know what I see as the difference."
 
"The UL77V is a surface gap pl

"The UL77V is a surface gap plug which hit the scene via OMC in the early 1970's.

Although it's heat range is listed as 77, it is actually a cold running plug as are all of the surface gap plugs. As such, it has always been prone to fouling.

Its main advantage is that they almost last forever.

Some engine even became hard starting when using the surface gap plugs. At some point in time, also in the early 1970's OMC came up with an assortment of electrode type spark plugs, at least three or four different types of which I do not recall their designations BUT I do recall that the final designated spark plug was the Champion L77J4 which proved to be the perfect alternative plug.

The gap of the L77J4 plug was recommended to be set to .030, and this was due to the early electronic ignition systems (Battery Capacitance Discharge) being dependent on battery supplied voltage and the needed components of those days of a distributor cap and rotor that created extra gaps to jump.

When the newer type electronic igniton arrived on the scene (Magneto Capacitance Discharge) in 1973, the recommended gap was changed to .040 but only for the engines from 1973 up.

After a short time, the L77J4 plug became L77JC4 with a improved center electrode being copper, hence the "C", and shortly thereafter the "Q" (suppressor) joined the group to form the QL77JC4.

It seems to be that 98% of the OMC engines with the Battery Capacitance Discharge ignition run better with this QL77JC4 plug set at .040.

There is however that 2% of the OMC engine that for some reason run better with the UL77V surface gap plugs, and this could be two identical engines side by side, one running the surface gap, the other running the electrode plug.

The last time I asked a factory rep how this could possibly be, I believe it was around 1983, he suddenly had to take a phone call and said that he would get back to me. When he gets back to me, I'll relay that informatiuon to you."
 
you never cease to amaze me Jo

you never cease to amaze me Joe!!! I guess since I have all 3 I'll find which ones work the best. Thanks for the info. I would like to know why the UL-77V plugs are listed as racing application if they are a cooler plug? Why not use the conventional electrode plugs?
 
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