Spark plug compatability/swap, , 1973 7.5 Merc vs 1979 Merc 9.8

Spark plug compatability/swap, , 1973 7.5 Merc vs 1979 Merc 9.8
I have a new set of gapless Champion L78Y from a 1973 Merc 7.5 hp with the phase maker ignition with the red module. I am going to run a Merc 9.8 1979 that has the proper gap plugs in it that the engine calls for, “Champion” L77JC4.
Am I asking for trouble to see how these gapless plugs run in the newer motor.
I read on this forum (when I was searching for answers ) that the gapable plugs seem to cause the engine to idle(troll speed ) more smoothly. I don’t necessarily need these plugs, just checking cause am dissolving a partnership and will give them to the new owner of the Phase Maker.
is 40 thousands the correct gap for the L77jc4. (my manual don go that modern)
THX
B521

The gapless plugs can only be used with the CD ignition (black switch box). The magneto and Phase Maker (when it's working) won't fire them.

Jeff

Hey Jeff how doin thx for reply.
I have been using the gapless plugs in the phase maker since I got it in the late 70's. Probably only like 350 hours on that motor. If it makes any difference it is the phase maker with the red module. (circa 1973 sn 3731914 Merc 7.5 ). Yes it has the points also of which the Merc manual states that the points will become charcoal colored black and pitted etc, but not to worry about them as they may outlast the life of the engine , but the high power/ of the phase maker will overcome the deterioration and still fire on the points signal etc. I realize that is a bit of a stretch, . so now I am confused. What I am going to do now is go borrow that old Merc manual and see what they call for, cause I am not sure if the first set of plugs were gapless. the moter was almost new when me and partner bought it but he may have did a plug change sometime down the road, don't know for sure.
Also i guess your telling me that i can use the gapless plugs in the 1979 9.8
merc as it has the black box

The Merc Manual lists all gapless plugs for the phase makers, what is listed for the 1973 7.5 is L78V, which is what I have. (sorry as in the previous reply I made a typo and typed L78Y. (SO ITS NOT A Y ITS A V).

The Phase Maker ignitions have enough problems without having to fire gap less plugs.

Jeff

Jeff, and kim, Much Thx
I found different opinions on these gapless plugs. I agree with Jeff as in don't muck with the phase maker. Kim, I must have got lucky as this stupid module phase maker did not foul the plugs. these first set of plugs did not foul much at all, say 300 hours with 70 percent trolling speed, all they did was wear down the height of the center electrode a few thousands of an inch. When I took them out i put them in a can with an inch of lacquer thinner to soak and next day took them out and they polished up with a cotton rag, I mean clean as new. I had to run a few tests with the performance of this motor and for the heck of it, I switched the same type gapless plugs with brand new ones and the 30 year old ones and it ran good on both sets of gapless plugs.. Regardless I AM STICKING WITH THE GAPABLE PLUGS ON THE 1979 9.8. (L77jc4) My former partner is buying me out on the 7.5 phase maker and he can use what he wants,
Just for discussion what I find people saying is the standard electrode plug will produce a smoother idle and the gapless plugs are only a slight advantage at WOT.
I was just checking to see if i could use the gapless plugs on the 1979 motor to make sure I would not cause a premature failure of the controll box (because I had an extra set.
What all outboards are out there that just have the old fashioned points condenser and coil an distributor. old sea king, or a old johnson, or old chrysler, I need an old hobbie motor to tinker with, (preferably low horsepower) and I don't want to be handicapped with proprietary complicated electronics in its future. (maybe best to start a thread on that topic.???
Thank you gentlemen
I will be back.

I have read that the gapless plugs work best "for sustained high speed running" (paraphrased from my OMC service manual).

A gapped plug will give you better cold starts, lower rpm running (idle and trolling speed) etc.

My 140 Ev (90 degree V4 looper) can run either the surface gap or gapped plugs - not scientific but I find running the gapped plugs it runs a little smoother and does burn a little less gas (but not a huge gas savings, but when you burn 80 gallons a weekend, even saving half a gallon adds up over time - and that I did track with the fuel flow meter). Now, this motor is on a 25' walk-around cuddy and I rarely run it faster than "cruise speed", which may make the difference on my application.

On a small merc, I would absolutely use a gapped plug and in this case DO use the Champions, not NGK's (even if they cross ref). The older merc ignitions (Phelon and PhaseMakers) lacked the voltage level to properly fire the NGK's which should be used with the (T3/T4 Thunderbolt ignitions)

Graham
First thx
second, sounds like everybody is in a general agreement. Lot of info presented here so as anyone researching/searching threads will get a good basis of experienced knowledge.
A QUESTION FOR CLARIFICATION. yOU ONCE TOLD ME THAT MY 1979 9.8 WAS AN EARLY T4 thunderbolt. going by your previous post , you suggest I use the NGK equivalent and would it be OK to use the champions, (both gapped plugs) Is this correct.
Does anybody have a reference as to mercs years of what is a t3 and a t4 etc etc for these portables say up to mmm 25 horse power .

when they quit making 2 cycles what were they classified as ?? I guess your talking about 1999 or something.

(early t4 as opposed to late t4) ??? maybe it has the same principal operation but uses different parts.

Yes, a 79 7.5 had/has a T4 ignition. The T3 (which was a modular T4 kinda sorta) and the T4 produce considerably higher voltages than earlier ignitions OR OMC and Suzuki ignitions.

I'm not totally up on it but the NGK's plugs resistance is different than Champions even if the heat range is the same etc and they (the NGK's) fire "as designed" with the higher powered ignitions - the Champions are not totally capable of utilizing all the power being produced. So, if you can't get NGK's, Autolites are the "next best thing" if you have a T3/T4 ignition.

And yes, as long as there is "room" at the top of the cylinder, I will run a gapped plug.

Regarding the ignitions, I can give you a (probably almost completely correct) listing here going back to 1965.

1965- 1969 = all models 35 horses and below had a Phelon ignition

1970 - 1972 = 20 horse and under all switched to the "new" Phase Maker and the 40 horse (all by itself got to test the Thunderbolt 3)

1973 - the Thunderbolt 4 was first introduced and used exclusively on the 20 horse model. The T3 was mothballed and the 40 (reverted) to the Phase Maker which was also used (still) on the 4, 7.5 and 9.8 horse models.

1974 - the 4 and 40 horse models kept the Phase Maker, all others (under 40) got the T4 ignitions.

1975 - the 40 horse finally got the T4, leaving the 4.5 horse as the only model, sub-40 horse, that used the Phase Maker. The 4.5 never changed and still had the PhaseMaker in it's last production year (1985).

1976-1979 all models (save the 4.5) continued to use the T4.

1980/81 - a 3.6 horse was introduced and they resurrected the T3 ignition for this model (probably had a bunch in the stock room). In 1983 the 3.6 became the 3.5, the ignition remained. The model bit the dust, along with a bunch at the end of 1985 when they came out with the "totally new line"

1984 - 1989 - the 2.2 horse (single) was introduced with the (ancient) Phelon ignition - used until they scrapped the model.

1986 - the 4.0 replaced the 4.5, but kept it's Phase Maker ignition. In 1988 Merc finally "relented" and put the T4 into the 4.0 horse models.

1986 was the new model line - the 6/8/9.9 all had the T4 as did the 20, 25 and 35 horse models.

From 1986 on, until production totally ceased in 2012, all portable 2 stroke Merc's, that were actually Merc's, of 4 horses or higher, with not more than 2 cylinders, used the T4 ignition.

The Yami/Mariners naturally had a Yamaha ignition and there was some single cylinder (2-5 horse range) plus the 25 horse "saltwater" that was built by Tohatsu and used their ignition system, that were out there when 2 strokes were still being made.

I may have missed an "odd ball" here or there and the above may be a little convoluted, but I think it's pretty well correct.

(later notes - the 15 horse was introduced in 1988 with the T4 - and YES, the 9.9 and 15 horse 2 strokes stayed in production until the 2012 model year "for export only" - up here in Canada I could have bought a "brand new" 2012 9.9 (that was mechanically identical to the the 1994 1/2, 9.9 (which was the year that the 9.9 began sharing the 15 horse power head) and save the displacement was about 99% identical the very first 9.9 models which hit the stores in mid 1985. The T4 ignition may have been the most successful ignition of all time. It changed very little since it's inception (they refined the switchbox and upgraded the coils fairly early on) but basically I could swap parts between a late 70's model and a "brand new" 2012 model.)

One bad thing about gapless plugs is that you can't read them for color (fuel air mixture). Just this morning I ran a triple with CD ignition on regular plugs to see what she was doing.

Jeff

I'm thinkin you are 100 percent correct, and it is a very GOOD point. Imagine a marine rookie backyard mechanic like me, missing that when I would be thinking, hmmm nothing wrong with the plugs, I'm telling you all that this marine outboard stuff is really tricky compared to basic auto mechanics, in this case you think that you are looking at something, but your not. geeeze Its like doing brain surgery on a vulcan (mr. spock)
and that's why the ones with a lot of use on them, cleaned up so well for me, cause there was no ceramic involved to help access what was happening. nor much of an exposed electrode tip.

fastjeff said:

One bad thing about gapless plugs is that you can't read them for color (fuel air mixture). Just this morning I ran a triple with CD ignition on regular plugs to see what she was doing.

Jeff

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Hey Graham your post is getting printed in quadruple., copy going into a fireproof vault , a copy in my workbench, and I am going to bury one with no treasure map, and a copy in my will for my son.

you said you may have missed a fine point here or there, I kinda of doubt it. what this really does is show the scope of the whole playing field so now when someone wants to scope down for some minute area they will have a great general understanding of the big picture. my guess is you are either highly schooled both academic and technical hands on in at the very minimum mERC mARINE AND YOU MAY HAVE BEEN A TECHNICAL TEACHER AFFIALIATED WITH MERC. (sorry 4 the caps) or your Carl K------- ,,, pronounced (Key Ka fer's ) illegatimare son.

galamb said:

Yes, a 79 7.5 had/has a T4 ignition. The T3 (which was a modular T4 kinda sorta) and the T4 produce considerably higher voltages than earlier ignitions OR OMC and Suzuki ignitions.

I'm not totally up on it but the NGK's plugs resistance is different than Champions even if the heat range is the same etc and they (the NGK's) fire "as designed" with the higher powered ignitions - the Champions are not totally capable of utilizing all the power being produced. So, if you can't get NGK's, Autolites are the "next best thing" if you have a T3/T4 ignition.

And yes, as long as there is "room" at the top of the cylinder, I will run a gapped plug.

Regarding the ignitions, I can give you a (probably almost completely correct) listing here going back to 1965.

1965- 1969 = all models 35 horses and below had a Phelon ignition

1970 - 1972 = 20 horse and under all switched to the "new" Phase Maker and the 40 horse (all by itself got to test the Thunderbolt 3)

1973 - the Thunderbolt 4 was first introduced and used exclusively on the 20 horse model. The T3 was mothballed and the 40 (reverted) to the Phase Maker which was also used (still) on the 4, 7.5 and 9.8 horse models.

1974 - the 4 and 40 horse models kept the Phase Maker, all others (under 40) got the T4 ignitions.

1975 - the 40 horse finally got the T4, leaving the 4.5 horse as the only model, sub-40 horse, that used the Phase Maker. The 4.5 never changed and still had the PhaseMaker in it's last production year (1985).

1976-1979 all models (save the 4.5) continued to use the T4.

1980/81 - a 3.6 horse was introduced and they resurrected the T3 ignition for this model (probably had a bunch in the stock room). In 1983 the 3.6 became the 3.5, the ignition remained. The model bit the dust, along with a bunch at the end of 1985 when they came out with the "totally new line"

1984 - 1989 - the 2.2 horse (single) was introduced with the (ancient) Phelon ignition - used until they scrapped the model.

1986 - the 4.0 replaced the 4.5, but kept it's Phase Maker ignition. In 1988 Merc finally "relented" and put the T4 into the 4.0 horse models.

1986 was the new model line - the 6/8/9.9 all had the T4 as did the 20, 25 and 35 horse models.

From 1986 on, until production totally ceased in 2012, all portable 2 stroke Merc's, that were actually Merc's, of 4 horses or higher, with not more than 2 cylinders, used the T4 ignition.

The Yami/Mariners naturally had a Yamaha ignition and there was some single cylinder (2-5 horse range) plus the 25 horse "saltwater" that was built by Tohatsu and used their ignition system, that were out there when 2 strokes were still being made.

I may have missed an "odd ball" here or there and the above may be a little convoluted, but I think it's pretty well correct.

(later notes - the 15 horse was introduced in 1988 with the T4 - and YES, the 9.9 and 15 horse 2 strokes stayed in production until the 2012 model year "for export only" - up here in Canada I could have bought a "brand new" 2012 9.9 (that was mechanically identical to the the 1994 1/2, 9.9 (which was the year that the 9.9 began sharing the 15 horse power head) and save the displacement was about 99% identical the very first 9.9 models which hit the stores in mid 1985. The T4 ignition may have been the most successful ignition of all time. It changed very little since it's inception (they refined the switchbox and upgraded the coils fairly early on) but basically I could swap parts between a late 70's model and a "brand new" 2012 model.)

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Hey Kimcrwbr1, I extend my apologies, as you will see in a post from fast jeff and an answer from me to him thatI would not actually know visually if the gapless were fouling or not so I will consider your statement that they can foul out more than normal .as good advice ..thx

kimcrwbr1 said:

http://store.oldmercs.com/Default.asp
According to these guys the L76V plugs can be used I just never been a fan of surface gap plugs more prone to fouling out.

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Actually I am simply the son of a small engine mechanic (who was also an automotive machinist and diesel mechanic).

Sometime in the late 1970's my Dad was working on a (relatively new) Merc. He got one mother of a shock from the "new fangled" ignition system that "didn't even have points"

Anyhow, from that point on, if I was around to help out, he would throw the manual at me anytime a CD ignition came into his shop (the bulk of his work was lawnmowers/chainsaws etc, outboards was a pretty small percentage for him).

However, he wouldn't let me become a mechanic (his words - a dirty thankless job). I joined the Air force (Canadian that is) but never really got too far away from outboards - particularly Merc portables. When I retired I took on (steady) part time work at home - mostly rebuilding carbs for a local marina since the modern techs can't find the DDT port on a bank of carbs and doing general service on 25 horse and under 2 strokes (easy to handle in the garage).

When Dad turned 70 (almost 10 years back) he finally gave up working but I still get him to set up points for me when I occasionally take on a vintage motor - I try to "only work" on "new fangled ignitions"

My, we sure have a lot in common, Graham.

...."1973 - the Thunderbolt 4 was first introduced and used exclusively on the 20 horse model. The T3 was mothballed and the 40 (reverted) to the Phase Maker which was also used (still) on the 4, 7.5 and 9.8 horse models."

Never knew the 40 hp Mercs used a Phase Maker. (According to my parts book it used the usual pointless stuff.) The 1970 Merc 40 twin had some oddball deal that used a switch box. I'm confused here; please straighten me out (if that's possible!)

Jeff

PS: For some reason--per my experience--the wretched Phase Maker system works fairly well on the single cylinder Mercs. None of them had a kill switch, which may be the reason why. It seems that, opening that normally grounded circuit, tends to mess up the P M system. I permanently ground that wire to the block on all of the P M twins I work on and toss out that assbackwards kill switch.

The high energy spark is needed to avoid fouled plugs--important on 2 strokes!

The system discharges itself when the motor stops. No danger.

Many a "10 and 15 hp" motor is actually a 25 with the, ah, appropriate decals!

Jeff

Jeff - I think you have pointed out an error in my notes (or at least a misinterpretation on my part).

In 1973 the "model 40" had the phasemaker - I mistook this to mean the 40 horse. Upon further reading, the 40 horse, in 1973 was called the model 402 (40 horse) and had the T3 until it got the T4. I will correct that note for future "historical" reference


Now as to the ignition power. I probably have notes on that too somewhere but will go off the top of my head here. I'm thinking that the OMC ignitions produce about 65,000 volts at the coil, portable Merc's are somewhere in the mid 80K range and 30'ish horse and up were either at or just over 100K (I'm probably off here, but that is probably close to the actual spread/difference) - and I'm only talking CD ignitions here - not the newer PCM/computer driven style (that I think Motorola either designed or initially built for Merc).

And agree with Jeff about discharging before work - nothing to worry about. I don't know if the capacitor(s) inside the switchbox stay charged or not (maybe), but unless you cut the box open (it's epoxy sealed), nothing to worry about.

And yes, I am not a 4 stroke fan (except in the tow vehicle) but I had a really good look at the 20 horse when they introduced it a couple years back. It was/is nice and light and the initial tests looked good (was talking with a technical rep at one of the major boat shows about it). It looks like in the last year or so (losing track of time now) they moved the 15 horse 4 stroke to the same powerhead - so I would add the (new) 15 to my "might be able to live with it if" list for 4 strokes.

However, all else being equal, I would opt for the 20 horse since it's the same platform and the 15 is the "detuned" model - the displacement is matched to the 20 and the weight is the same - no reason not to go with the 20 unless you run on HP restricted waters.

Now if you wallet is having trouble containing all it's cash there is the Evinrude ETEC 15 horse HO (DI 2 stroke) or the ETEC 25 are viable options in this horse class. But at 190'ish and 170'ish pounds respectively that's awful heavy compared to the 4S 15/20 Merc that comes in at about 115 lbs.

These little 4S Merc's are 100% Tohatsu's but since Merc buys in "bulk" they tend to be a little cheaper when Merc branded compared to either Tohatsu or Nissan (which is also the exact same motor), and Merc has a better service network (but certainly worth a look - the one Tohatsu dealer in my piece of Ontario gets some wicked "show special" deals from Tohatsu from time to time - so if in the market, do keep your eyes open).

In the used market it's tough to beat, for quality/durability/power the 25 horse Merc 2 stroke. I don't know exactly when Tohatsu started building them, but those were sold as the 25 "Saltwater" edition (and one other model whose name escapes me) were Tohatsu's.

But I'm thinking it was pretty "late", possibly at some point "after" Merc stopped selling most of their 2 strokes (maybe 2005'ish) in the US market (but maybe not quite). I have little to no experience with these Tohatsu built models.

The earlier ones, like most portable Merc's (at least those post 1986) were Merc's assembled from mostly Yamaha built parts - but Yami built the parts for Merc and never used them themselves - unlike the Mariner models which were really Yami's with different stickers. So the 25's I'm talking about were going back to the 25XD models up to (minimally) the 1994 1/2 models and including the Marathon and SeaPro models (Merc and Merc/Mariner "real" Mercs).

A late 80's 25 Merc is probably one of my favourite motors from them (along with the 4 cylinder 40 horse and V6 135, to round out the top 3) - almost impossible to kill, even if you are a little complacent looking after it, still "portable" @ 120'ish pounds and tons of guts.

Looks like Carl's dopey "multiply the hp by ten" model naming nonsense struck again!

I ordered parts for a Merc 40 once and got single cylinder stuff! Oh, the embarrassment.

Jeff

i have to admit that comment is funny.

fastjeff said:

Looks like Carl's dopey "multiply the hp by ten" model naming nonsense struck again!

I ordered parts for a Merc 40 once and got single cylinder stuff! Oh, the embarrassment.

Jeff

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Graham and Jeff pls check your private messages
Bernie