GAPLESS PLUGS can i switch??

[jim pate]

i have a 72 merc 65 hp it has those wierd no-gap plugs is there a regular plug i can use??any part numbers would be appreciated.thanks in advance jim

[tombrown]

Jim, there are some folks in here who have credentials such that you should dismiss everything I am about to say if they reply. In my own defense, I would suggest that I'm no stranger to outboard engines but I don't do it professionally and I'm not qualified to change some of these guys' spark plugs.

OK, the recommended spark plug for my engine in 1977 was the Champion L76V. Yours is probably the same, but check it out to make sure. Call your Mercury dealer if you don't have a manual. In 1987, Mercury recommended substituting the NGK BU8H in place of the L76V.

I would recommend that you follow Mercury's advice. If your engine was supposed to take an L76V in '72, spin in a set of NGK BU8Hs and be done with it. I would recommend against experimenting with heat ranges or styles if you're running a stock engine. Mercury knows the best plug for their engine. Spin in a fresh set every season.

If you are experiencing fouling, look to see the cause of the fowling, rather than fooling with your plugs. I think the 65 was an L4 in '72. Is that correct? Are you experiencing plug fouling, or do you just want to save a couple of bucks per year on plugs? If it's the later, don't. It isn't worth it. If it's the former: what is your compression on each hole, do you have fuel misting out of your carbs, what exactly do the plugs look like when they foul and can you describe the rest of the symptoms as best you can.

I don't care for the price either, so the next time I place an order with Rickracer (www.rickracers.com), I'm going to throw a couple of sets of plugs onto the order.

Don't overlook fuel problems. First, get the right fuel. Go with 89 octane non-oxygenated fuel if you can find it. If you can't find it, you might try blending some 100LL in with your 87 non-oxygenated. I'd go with 25% AV Gas as a test. The old L4 engines can idle super smooth if everything is right. Start with the right plugs and the right gas and see how it runs.

In defense of these guys (from your response to my other post), the real gear heads here probably weren't running 65s in 1972. There was a 650xs engine and a racing class to go with it, but I think that was later than '72. I'm not sure. I had good luck because lots of these guys used to run the old L6 Mercurys back in the '70s. Those who are not yet stricken with alzheimer have a lot of knowledge to share with me because of their first hand experience. I had an L4 50 horse engine way back in the early '80s. Let me know how it goes and I'll do what I can.


Good luck,

Tom Brown

[tombrown]

One more thing, if you're having idle problems, have a look at the back drag air jets on your carburetors. I think you have two side bowl carbs. The back drag jets are on the top of the bowl. Pull them out and see if you can get it to idle better. If so, look at up-sizing those jets about 2 or 3 sizes. In other words, if you have .035 back drag jets now, step up to .039 or .041. From what I can tell, it isn't possible to make the old engines idle properly with the original back drag air jets in place. Those old carbs were designed for a different generation of fuel.


Good luck,

Tom Brown

I use the Bosch Platinum plugs. The tip cleans itself with every spark, it heats up faster and can withstand higher temps. I find the amount of clearance I have and number of threads in the head then pick an average heat range and start from there going up or down by reading the plugs. Plugs will tell you EVERYTHING. Its a little work but I have more confidence in my Engineering skills than the factory guys. ;) When testing a particular rpm range, don't make a run and idle 2 miles back to the dock and expect a good reading. Make your run and shut the motor off right there and check the plugs. Its a little work but you'll be right on the money.

-bll

[WillyT]

I had excellent luck with the AC gapless plugs that were direct replacements for the Champions on my 1977 Merc 175. I always bought them at NAPA, and the price was pretty good, as I recall. The reason I went to AC was because the Champions, per my Merc mechanic/guru, had a history of developing minute hairline cracks in the insulator (could not see them with the naked eye), and they would stop sparking. All of this was just theory until it actually happened to one of mine (and left me with a dead cylinder). Never had that happen with the AC, and I used that engine for 10-15 years with the AC plugs. To me, a gapped plug was just a piece of metal waiting to break off to destroy my engine.

[jim pate]

TOM, thanks for the reply,yes you are correct it is a l-4 motor i'm and old gearhead with i/o's that's all i've owned for the last ten or so years ,i havent had an o/b in probably 15 years, so i'm trying to get back up to speed so to speak, i dont have any fouling problems and money really is'nt a factor it was just for ease in locating these plugs,i may have jumped the gun a little before researhing but figured these would hard to come by at the local auto parts store pleas correct me if i'm wrong. i've got lots of questions about my set-up and am seeking more performance out of what i've got no, it's not a new or super-high dollar boat in fact i paid 1000.00 for the whole rig and took it to the lake the day i bought it. it's a arrow-glass scorpion a small (14'8) fiberglass shallow v-hull with above motor, it's hole shot is terrible and top-end leaves much to be desired, it wont tach but 3100 on the old airguide tach in the dash (which hardly moved at all on the first two or three outings)so the tach is suspect.i'm getting 26mph out of it now surely i can squeeze a little more than that. more text to come thanks jim

[Raceman]

Some people will disagree with me, but I've never run anything but the surface gap plugs you're speaking of. Especially in a relatively low performance engine like you're speaking of, there's just no reason to change. In the mid 70's I lost the center electrode out of a surface gap Champion, destroying a powerhead, and if the dealer told me the truth at the time, Champion's response was "sorry, we'll give you a new sparkplug". I've never run another champion plug in anything since and never will. I've run AC's every since and so far so good. As far as reading plugs and rejetting a 4 cyl. 650 there's not enough performance difference between engine damagingly lean and way too fat to be worth the trouble. If you're looking for more performance from that engine, you'll have to do it by optimizing the set up with the boat and blade.

[jim pate]

race thanks, i figured this motor was never ment to be a hot-rod and i'm sure i can do some things to improve it's runs the former owner didnt even drain or sta-bil the fuel during winters,so i'm assuming the bowls probably need cleaning,i'm nbot sure if it has points??if so they need checking,as far as the prop it has no marking whatsoever,so i dont know what it is or even what i need to get for it.someone at some point installed a alluminium fuel tank it looks like about 15 gals in the frnot of the boat!!!not all the way to the front but a little ahead of the drivers seat i think going to the rear with the tank(s)would have to help with the set-up also cause with a full tank it sits bow heavy in the water. the motor is really good to listen to, even my wife commented it was real quite and smooth running but i need more speed!!! thanks to all jim

[Glenn]

Hey guys. What's the part number of the AC gap-less plug. I've got the champions in my '78 175.

Glenn

[Dave Estes]

AC-V40FFM