Which spark plugs

[Scott Sutphen]

I'm getting confussing information about which plugs I should be using. I have a 120 Johnson, model J120TLAEM, serial#02306410. Can anyone tell me exactly what year it is and what the other letters mean. The local dealer gave me Champion QL82YC plugs. Clymers manual gives two different choices. The motor runs good and strong, but I have to clean plugs every other trip or it misses out for the first 10-15 minutes. Most of my running is WOT or 3/4 throttle pulling skiers or running to a fishing hole. Very little time trolling or slow speed. Whats the best plug for my motor and what gap!

 

[G DANE]

Re: Which spark plugs

I cant make your model nr. match a year, but OMC Plug chart advises pre 1993 120 HP V4 loopers to use QL77JC4 or QL16V surface gap plugs. All later than 93, QL78YC. Only information I have.

 

[OBJ]

Re: Which spark plugs

Either the "A" or the "M" is wrong in the model number tightline....could ya' take another look?

 

[Mettaree]

Re: Which spark plugs

1989 model year<br /><br />

 

[Dhadley]

Re: Which spark plugs

In 1989 the A replaced the C and means Alternate color. Most likely yours is charcoal instead of white.<br /><br />The water routing was changed in 93 so you could (with a 93 & newer) run a warmer plug. I still would opt for the cooler 77 in mine.<br /><br />Good luck!

 

[Joe Reeves]

Re: Which spark plugs

You've mentioned nothing about the compression and spark. Compression should be approx 100+ psi and even on all cyls. With the plugs removed, spark should jump a 7/16" gap with a strong blue lightning like flame.... really a strong wide blue snap!<br /><br />If the above checks out okay, personally I would revert to the original spark plugs recommended for that engine which would be the Champion QL77JC4 plugs, gapped at .040 (Not .030).

 

[Scott Sutphen]

Re: Which spark plugs

I double checked the model #,J120TLAEM is right from the sticker on the transome mount. The motor is charcoal. The engine wiring is the same diagram that shows in the Clymers manual for a 1988-1990 120hp. I have 125-130psi compression on all cylinders. I'll go with the recommended plugs and gap. Thanks for sharing your knowledge.

 

[seahorse5]

Re: Which spark plugs

Originally the motor came with QL77JC4 plugs, then about '96 it was changed to QL82YC, then within a year, OMC changed all plugs for loop charged motors 40hp and above to QL78YC for consistancy. The annual factory parts and accessories manual has the only up to date approved chart for plugs.<br /><br />The Y in the plug number means and extended nose and it give a better idle and midrange for looper motors. Gap them to .030".

 

[walleye052974]

Re: Which spark plugs

I would try the surface gap plug since you run top end alot. It also sounds like you are running very rich.

 

[alumistar]

Re: Which spark plugs

Just for fun, look at conversion charts. Find conversions into NGK(V-Power), Bosch(Iridium), SpliFire, or something of the sort that manipulates the size,shape and heat of the spark kernal. I heard stories both ways about these types of plugs. I'll tell you this, in all of the 2-cycle dirt-bikes, snowmobiles, and jet-skis that I have seen. The best performing ones WERE using those types of plugs. Granted there are more performance "named" plugs, then there are "real" performance plugs, I know the ones I named did what they clamed with the exception of SplitFire, the engineers were what you would call "a bit more optimistic with their media department than they should have been!

 

[ReelDrag]

Re: Which spark plugs

I have a 92 Johnson 115 crossflow. Went to my local dealer for plugs. He gave me QL82YC. He said these motors run better with them. Haven't tried them yet. Should I take them back?

 

[seahorse5]

Re: Which spark plugs

Hey ReelDrag,<br /><br />A crossflow V4 takes the QL82C plug. The ones you have, QL82YC have a long nose on them and could possibly hit a piston. Take them back and exchange them for the right ones.

 

[Dhadley]

Re: Which spark plugs

If you run a QL82YC in a crossflow V4, no matter what you gap them at, after you run it they will be gapped at .009".<br /><br />Trust me.

 

[ReelDrag]

Re: Which spark plugs

Thanks for the info. I've been using the QL77JC4 plugs. Motor loads up after trolling for awhile but clears up after giving it some rpms. Is it ok to go with the hotter plug? This powerhead only has 58hrs on it. Don't want to fry a piston. I premix with Pennzoil synthetic blend and Chevron 93 octane.

 

[ReelDrag]

Re: Which spark plugs

Thanks for the info. I've been using the QL77JC4 plugs. Motor loads up after trolling for awhile but clears up after giving it some rpms. Is it ok to go with the hotter plug? This powerhead only has 58hrs on it. Don't want to fry a piston. I premix with Pennzoil synthetic blend and Chevron 93 octane.

 

[Dhadley]

Re: Which spark plugs

The oil is a great choice but I would switch to the recommended 87 octane. Unless you are running higher than stock compression.

 

[ReelDrag]

Re: Which spark plugs

I've tried the lower octane, but it seems to start better when cold with the higher octane.

 

[Dhadley]

Re: Which spark plugs

If youre going to stick with high test fuel, definately stick with a cooler plug. It wouldnt hurt to richen up the mid range jet a couple of numbers too.

 

[rickdb1boat]

Re: Which spark plugs

reeldrag,<br /><br />What are you gapping the QL77JC4's plugs at? Gap at .040 for trolling. It will fire better under low speed conditions and foul out the plugs less. I use .040 all the time no matter the speed on my QL77JC4's with no problem at all, in a different sized motor, of course. But the wider gap does help...

 

[ReelDrag]

Re: Which spark plugs

I gap my plugs at .035. Why would I need to use lower octane fuel with a hotter plug? Please explain.