Why different spark plugs?

[buzzcutt]

I have just acquired a 17 mako with a 1989 88hp Johnson. After a few trips i decided to pick up some new spark plugs (QL77JC4). When I removed the Plugs from the motor I found Champion RL82C plugs in the motor.

Why would those be there? Do they run hotter to reduce fouling? Cooler for better high speed operation?
Would they be used to make the engine run better should there be a problem with the motor?

If anyone has an idea, I would like to hear it.

Thanks,
BuzzCutt

 

[DJ]

Re: Why different spark plugs?

The plugs you bought are the right ones. Gap them at .040" and it will idle better.

 

[Rudy Brown]

Re: Why different spark plugs?

My 84 90hp rude uses either L77JC4 or L82C. It came new with QL82C. I havent noticed much difference in performance between the two. The Q and R are resistors in the plugs that need to run so it dosent interfere with the VRO. If you premix(like I do) you wont need the resistor.

 

[DJ]

Re: Why different spark plugs?

I do not see the connection with resistor plugs and the oil injection. The oil injection is mechanical.

 

[jtexas]

Re: Why different spark plugs?

Q designates champion's radio frequency interference suppression plug. Plug noise on your stereo or fishfinder is caused by RFI. Sometimes RF interferes with capacity discharge ignitions.

 

[imported_lorin]

Re: Why different spark plugs?

Yeah, what jtexas said. Also, the Q type plug is really an inductive resistor plug. Its use is very critical on motors with the optical iginition system. Without them the engine will be misfiring.

 

[Dhadley]

Re: Why different spark plugs?

On the oil injection, the theory is that the non-Q type plugs may, or could, interfere with the electronic part of the pump that has to do with the alarms etc.

 

[Texasmark]

Re: Why different spark plugs?

Boy, I tell you what. You just keep learning on here. Every day is a different amazement.

Since we are on plugs, I asked the question yesterday, maybe it's answered and I haven't gotten there yet, about surface gap vs normal plugs.

I presumed the surf gap was supposed to last longer. I run em and have run em, but I never liked the carbon track across the porcelain that you get that you don't have with normal plugs.......but with microsecond firiing of the ignition coil, maybe it doesn't matter like it would with coils, condensers, and points. Course it doesn't seem to bother them as I ran my last set about 7 years (when I sold the boat) with stellar engine performance (Merc I6).

Mark

 

[Dhadley]

Re: Why different spark plugs?

There are several theorys about why any given plug style is better than the rest. One of the claims made about the surface gap plugs is that if any "path" gets fouled (from electrode to ground) there is an almost unlimited number of other "paths" for the spark to take.

I've run both styles in many different motors on many different boats (recreational) and to be honest, the only difference I saw was on the bill.

 

[Dhadley]

Re: Why different spark plugs?

Something worth mentioning -- all my dealings with motors have been at sea level. Walleyehed has a lot of experience with motors at altitude which may have some bearing on the discussion.

 

[buzzcutt]

Re: Why different spark plugs?

Thank you, one and all for your input on this issue. There is quite a broad knowledge base here. I am thinking I will be asking more questions as time marches on.

I have decided to go with the recommended QL77JC4 plugs and gap them at the djohns 19 recommended .040". I will run the boat Saturday and note any performance differences and spark plug condition. I will revise spark gap if required.

Again, thank you all,

BuzzCutt

 

[cougar1985]

Re: Why different spark plugs?

.040 is a good gap for trolling for sure,ive had mine gapped at that for 2 years now and find that for lots of trolling its good as my 90 hasnt even hiccuped in all that time and i troll alot.maybe i should have a trolling motor but it trolls so good i dont see the point.last week every body was still fishing for walleye and i decided to troll with the 90 and slayed them while everybody eles got nada. lucky i guess but ill take it anyway i can.lol.

 

[jtexas]

Re: Why different spark plugs?

Mark,
I thought surface gap plugs were invented for hi-compression racing engines with very little piston clearance. Or to get the plug back out of the chamber to raise the temp. It takes a very hot burn to keep 'em clean, as close to the wall as they are.

 

[Dhadley]

Re: Why different spark plugs?

That's another one of the theorys about the surface gap plug. If you pull the flame front away from the piston dome the combustion temps will be lower. That's OK but what about a complete burn? And the higher the rpm the closer a gap needs to be, to a point. We've seen some motors hit the "wall" at a given rpm, whether it's 7000 or 8000, with the surface gap plugs. Throw in a set of air gap plugs at .035 or .030 and gain rpm. We've had no problems with the air gap plugs at well over 8000.

 

[jtexas]

Re: Why different spark plugs?

I thought temp was more related to heatsinking...great, another one of those "things you thought you knew!"

But now I have a powerful new knowlege: Reduced Gap = More Power...let's start with .020 and work our way down form there...

8)

 

[Dhadley]

Re: Why different spark plugs?

Yeah, we ran into that with the race boats. It seems like you get to a certain rpm and it's like you hit a wall. Nothing like the "stock" rpm range. Sometimes it's the stator that just kinda gives up. Then we get a CDI race stator and away we go. Sometimes it's just the spark plug gap. It's really the whole combination that has to work together.

I was trying to remember at what rpm we found the gap deal on the V4. Somewhere in the low 7000 range I think. Eventually we got it to turn 8200 in the 1/4 mile.

 

[Texasmark]

Re: Why different spark plugs?

Hey D, Dan I think, Hadley.

Let's talk about Port Charlotte.

I know you guys really got whacked by a hurricane and can't remember which one since so many blow by there.

It may have been Katrina. Anyway, what's the "status of the apparatus"? You'all going to get things back together? Heart bleads for you man. I grew up on the Texas coast and served my country on the eastern coast, been down there and loved it....unless molly bell was blowing down your stove pipe.

Mark
Mark