1975 9.9 Spark Plug Questions

awaschka

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I have a 1975 9.9 which is used as a sailboat auxiliary. It is a long shaft electric start and has the workboat prop (10 x 5) and reverse thrust kit. Since new it has been bad about fouling plugs. The only solution I ever found was to use ONLY Johnson 2 cylinder oil. Recently it doesn't seem to matter what oil or plugs I use, plugs still foul.

Some time I ago I rebuilt the power head including a new reed valve and cylinder head. Looking into the spark plug holes it appears that the head is ported, i.e. the sparkplug opening into the cylinder has a half-dome over the tip that is only open on one side. It would seem to matter where the ground electrode is with respect to that opening, but there is no way to control that. I have read about automotive power engine builders "indexing" plugs with washer shims to get the electrodes aligned.

The original plug was L7J. Then I think UL88C was recommended, but Champion's web site says that Johnson recommends only Q series plugs or misfiring may result. Recently I have seen NGKs recommended.

Questions:
1. Should I be indexing the plugs? Neither the head threads or the NGK plugs are repeatable, i.e. different plugs in the same cylinder don't torque to the same alignment. Neither does the same plug in different cylinders. What is more important, the alignment or the "reach"?

2. What plug should I be using? I haven't found one yet that doesn't foul pretty quickly.

3. Any suggestions on oil to minimize fouling?

Thanks,

Al
 

bktheking

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Re: 1975 9.9 Spark Plug Questions

When you rebuilt it was it low on compression and did you hone the block and install new rings?
 

Elbo

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Re: 1975 9.9 Spark Plug Questions

Sounds more like a flooding problem.Im not sure what ur saying about the plug position torque.It doesn't matter which way the plug is facing while in the cylinder,as long as it is the correct length.Fuel and oil is what is fouling the plugs.That plug after being run should be a brownish color.If it is black and sooty,It is getting to much fuel.The float in the carb may not be shutting the fuel off.My guess would be a carb rebuild.Just put a carb kit in it and go from there.
 

bktheking

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Re: 1975 9.9 Spark Plug Questions

Agreed, plugs fouling have nothing to do with the plug itself, i'd start with the carb rebuild as well. Do you run synthetic at 50:1. Is the motor run wide open or just troll around, it is on a sailboat so I don't know. The reason I ask about rings is blow by, oil could be getting past the rings and you may be getting more oil in the cylinder than you need.
 

Elbo

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Re: 1975 9.9 Spark Plug Questions

No such thing as blowby on a 2stroke.There is no oil in the crankcase.The only lube that motor gets is from the oil you put in the gas. The crankcase is actually a vaccum caused by the pistons going up.Thats what runs the fuel pump.If the rings are worn out you would get a pressurized crank case.
 

bktheking

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Re: 1975 9.9 Spark Plug Questions

2 Stroke BLOW-BY

This piston didn't fail in operation but it does show the most common problem, blow-by. The rings were worn past the maximum ring end gap spec, allowing combustion pressure to seep past the rings and down the piston skirt causing a distinct carbon pattern. Its possible that the cylinder walls cross-hatched honing pattern is partly to blame. If the cylinder walls are glazed or worn too far, even new rings won't seal properly to prevent a blow-by problem. Flex-Hones is a product available at most auto parts stores. They can be used to remove oil glazing and restore cross-hatch honing marks that enable the rings to wear to the cylinder and form a good seal. If you purchase a Flex-Hone for your cylinder, the proper grit is 240 and the size should be 10% smaller than the bore diameter.


blowby.jpg


It does exist, but in this case may not be causing the issue, I think a comp check would show something.
 

Elbo

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Re: 1975 9.9 Spark Plug Questions

It can't blow by because its a piston ported engine The pressure is released at the bottom of the stroke out the exhaust or thru the intake.
 

bktheking

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Re: 1975 9.9 Spark Plug Questions

Right you are! So why is it then that from my research fouling plugs with everything proper (carb, tuneup) can be caused be severely worn rings/cylinders, you're saying there is no possiblity that it can get by the rings?
 

awaschka

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More Data Re: 1975 9.9 Spark Plug Questions

More Data Re: 1975 9.9 Spark Plug Questions

1. I rebuilt the engine due to a compression problem. The actual cause was a blown head gasket due to corrosion on the head. While I was in there, I went ahead and replaced the pistons, rings and reed valve.

2. The engine had very few hours on it, and still does. When I rebuilt it the cross hatch patern looked like it was new.

3. I did surface the new head at the time.

4. Now the compression is fine, maybe even a little high. It is reading about 105-110 on my gauge (calibration unknown) on both cylinders. I've got some seafoam and I'm going to decarbonize it when I get it running.

5. I have the carb out and soaking, but the float valve looks good, as does the float. I'll probably go ahead and replace them anyway. If the float was bad, would that cause the engine to run rough? Isn't that controlled by the jets? Seems like the carb would just leak fuel all over.

6. The plugs are black, oily, and one of them was shorted, no spark. Moved it to the other cylinder and the problem moved with the plug. I media blasted the plugs, cleaned them with solvent, blew them out with air and the spark looks good. I'm not planning on running them as there might still be some media imbedded in them, just wanted to see what happened if I cleaned them up.

7. So nobody seems to think that having the spark shielded from the mixture by the dome on one side and the ground electrode on the other is a problem?

Thanks,

Al
 

bktheking

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Re: More Data Re: 1975 9.9 Spark Plug Questions

Re: More Data Re: 1975 9.9 Spark Plug Questions

According to the spark plug application guide, 74-76 used UL81C. The Q series from what I have researched was for the later ignition systems and if used in a points system would foul almost immediately. Another recommended NGK B7HS as a suitable replacement for the champion plugs. The 81C is a hotter plug than the QL77jc4's, I suspect because the ignition system is weaker on the 74-76 motors. What are you using for a plug now?
 

BoatBuoy

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Re: 1975 9.9 Spark Plug Questions

You might try using the correct plug for that motor, which is Champion UL81C. The L7J is a different plug.

L = 14mm thread size
7 = Heat range
J = Cutback ground electrode

U = Auxillary gap
L = 14mm thread size
81 = heat range
C = Copper plus design

Even if everything else was the same, notice the difference in the heat range of your plug and the recommended plug. Higher number is hotter.
 

kbait

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Re: 1975 9.9 Spark Plug Questions

You have a points ignition system which gives a weaker spark than the '77 and newer CD ignitions. Try the NGK B7HS, or Champion UL81C. Both should work well w/your motor. Also, check the stator plate for lateral play. Move the flywheel clockwise by hand and look for any jumping of the plate. Popping the flywheel to check it is even better, just grab the plate and try to move it laterally. I have a '75 15hp electric, and I played hell with that problem, but I finally got the plate stabilized and all is good. If it can wobble/move laterally, it WILL change the point gap! and when you're wanting .020", any play will cause performance/spark issues. If you do have slop in the stator/armature plate,PM me and I'll tell you what I did to cure it. Common problem w/9.9-15's from '74-76. I guess they had a fix for it back when, but you cannot order the new stator plate, or whatever they did to fix it. Good luck.
 
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Chinewalker

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Re: 1975 9.9 Spark Plug Questions

To add to what kbait said, make sure once the plate is stabilized that the points are set at EXACTLY 180-degrees opposite each other. Check your TDC and set your timing so that a light or buzzer goes on at exact opposites. Those maker point ignitions worked alright when all was right but did have issues with fire if things were off even a little bit...
 

OptsyEagle

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Re: 1975 9.9 Spark Plug Questions

Get rid of your 7s and put in 8s (I'm talking about spark plugs here). You need a hotter plug. Fouling is the result of improperly burnt fuel mixture. The most common cause is a combustion chamber that is running too cold. A hotter plug will help. Now that being said, you do not want to keep going hotter, because too hot of plug will start giving you pre-ignition, which is an even nastier problem.

Now that being said, if your combustion chamber is too cold that can be from the plug but also from the cooling system. If your thermostat is failed open your motor will run cooler and the spark plugs will eventually foul. This situation usually happens over quite a few hours of use. If your plugs are fouling very quickly (a couple hours of use) then it is most likely too cold of plug.

The other issue is carbon. That is the material that is causing the fouling. A decarb can't hurt. Search this site for Seafoam decarb and follow those procedures.

Lastly, I have a 1975 9.9Hp Evinrude and find that it doesn't really like the champion UL81Cs. For some reason, I (and quite a few others) would get an intermittent failure (motor surging, then bogging down, then surging again) with those plugs. I changed to NGK B7HS and I not longer get that problem and I have used the same plugs for 3 years now with no fouling problems. So go for the NGKs would be my recommendation and as long as your T-stat is operational and your motor has been decarbed, you should be good to go.
 

jay mendoza

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Re: 1975 9.9 Spark Plug Questions

Indexing the plugs, yeah, I do it, point the ground electrode tip towards the exhaust port. Mark the plug insulator with a sharpie so you can see where the electrode is pointing, and then find the cylinder that it will go into and align with with about the reccomended torque, you have to make a little compromise sometimes.

The part around the plug tip in the combustion chamber is to deflect the charge from condensing on the plug at idle and fouling it.

I have had no problems at all running NGK B7HS plugs, they never foul. I have a 1975 9.9hp.

No offense, but everyone kind of missed it on blow-by. In 2-strokes, it's when the rings allow combustion gasses to leak past them on the power stroke BEFORE the exhaust port opens. The blow-by is not through the ring gap, no matter how excessive it may be. The blow-by is from the rings being stuck in the grooves with carbon build up, then they cannot expand and put their tension against the cylinder wall so they can seal. We run our racing McCullochs with .090" end gap on the rings and get no blow by, as an example. Blow-by as it relates to a 2-stroke has nothing to do with combustion gasses pressurizing the crankcase, although engines with stuck rings and blow-by will often have the transfer port passageways, and the crankcase sides of the reeds blackened with carbon from blow-by gasses.

If you ever see black on the sides of your piston skirts, below the rings, then you have stuck rings and need to do some sort of de-carb. Beleive it or not, rings are most prone to becoming stuck with carbon during break-in due to excessive oil and the resultant carbon formation from low speed running, which is why a SeaFoam, or OMC Engine Tuner treatment is so critical after break-in for long engine life.

I would be suspiciouse of your cork float, replace it with a plastic one, replace the float valve, and use B7HS plugs. Check I-Boats, they have all the good stuff!
 

awaschka

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Re: 1975 9.9 Spark Plug Questions

Thanks everyone. Here's a few comments about the questions asked.

Since I have the workboat prop (10x5), the engine runs at around 1/2 to 3/4 throttle on the sailboat. With the old prop, I ran it lower, but that was bad for fouling and didn't have the power to buck a headwind.

I've been using Quicksilver dino 2 cycle oil because I had some for my Merc 115. I'm going to get some Johnson/Evinrude next time - that was the only oil that never fouled. Is synthetic better about burning than dino?

L-7J is the plug that was recommended in the original manual and service manual. I think it was discontinued (but still available in the UK) and replaced with the UL81C. I think they changed the heat range scale at the same time so I don't think you can make a comparison between 7 and 81. I ran L-7Js in the engine for a long time with no problems except for one time when a dealer took out the thermostat. Then I ran UL 81Cs. Lately I've been running the NGKs (7s)

I'll recheck the distributor plate and timing. I've been using an ohmmeter but I don't remember checking them for 180 degrees. I'm not sure how I could change it if it is out, however.
 
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