Fouled Crankcase.-

[racerone]

Why would one carbon up more than the other ?

 

[jhande]

An old school automotive trick that works for decarboning engines...
Use a fine mist spray bottle full of water. Raise the RPM's above idle and squirt the water into the carb, repeat multiple times. The water turns to steam and breaks down the deposits. Think of steam cleaning.

Some behind the scenes of oil companies/brands...
There's more brands of oil than refineries. Lot's of oil is branded with different names although it's the same oil. Yes there is different qualities/specs that certain brands require. Sometimes there's not enough of that quality to fulfill there quota. They out source to other brands, a lot of times that other brand sells them there lesser quality of oil. Yes it happens even with the top name brand companies. The lesser known brands usually get the lesser quality oil. Yes lower quality oil can still pass certifications.

Carbon build up in the engine from OP. Could be from...
Oil/gas mix not correct
Spark plugs not hot enough
Carb(s) not adjusted properly
Extended low RPM run time
Just to name a few.

 

[Sea Rider]

This is a 2 stroke motor, old automobile decarboning trick doesn't apply here. the motor was manually decarboned before, a new head gasket with a light coat of Permatex Aviation sealer was applied and soon after evenly torqued to 30 NM in 3-10 NM consecutive torque steps.

Oil/Gas Ratio 50: 1 and probably a tad more.
New Spark Plugs BTHS-10, 1.0 mm gapped to.
Single Carb well idle adjusted. High speed Jets are fixed.
Extended low rpm runs + poor quality cheapo oil surely accounts for that scenario...

Happy Boating​

 

[racerone]

And why would ---" automobile decarboning trick " ---Not work here ??-----Parts and pieces / decarbon fluid have no idea whether they are working in a 2 stroke or 4 stroke engine.-------Yes , refineries will blend / package products for anyone who presents many beer tokens.-----Factories do the same.-----They sell " capacity " to any one with coins.-----Worked in a tire factory for a short career step.------Some tires had a competitor labels molded in.-----Other manufactures just shipped mold and specifications over.

 

[Sea Rider]

Because a 2 stroke motor will carbon up their combustion chamber and exhaust areas a zillion times more compared to an automobile, it's the nature of such filthy beast. Will add that those walls are porous ones and with hundreds of repetitive ON-OFF cycles will start to collect carbon particles as soon the motor is started and there's not a thing you can do about it. If plan spraying mist water thru the carb with motor running a much better and efficient cleaning procedure will be obtained doing same with a bottle of CRC carbon remover or any other brand of your particular choice.

Boaters have the wrong idea that such products will wash and clean the already carbon built up which is a tech fallacy, what carbon remover does is soften and wash what lays over the already carbon crust formations, keep piston rings in good shape, better compression and smooths out any motor not idling or running strong.

Happy Boating​

 

[racerone]

Took a 1983 model 9.9 Evinrude apart for inspection last week.-----No carbon in the ring grooves at all.---Little bit of carbon / black stuff on top of piston.----Just put pistons back in this afternoon.

 

[Faztbullet]

There is no wash on pistons domes....classic sign of low temp. If it was oil quality the plugs would foul from throw off. Motor has other problems

 

[Sea Rider]

Took a 1983 model 9.9 Evinrude apart for inspection last week.-----No carbon in the ring grooves at all.---Little bit of carbon / black stuff on top of piston.----Just put pistons back in this afternoon.

Year of fabrication doesn't say much, clocked run hours is all. That's why it's a must count with an installed hour/tach meter. If using good quality 2 stroke oils and fuel 50:1 mixed, spark plugs well gapped and in excellent shape, motor cooling properly and constantly run at speed won't find carbon build ups in the piston's grooves.

Did you checked the exhaust cover's internal chamber condition ? if the lower piston was found much cleaner, seems that on 2 stroke, 2 cylinder motors the upper piston carbons up way more than the lower one.

Happy Boating​

 

[Sea Rider]

There is no wash on pistons domes....classic sign of low temp. If it was oil quality the plugs would foul from throw off. Motor has other problems

What's no wash on pistons domes/heads ? low temp. That motor had all their water passages cleaned to mint factory conditions along installing a new OEM thermostat. The motor keeps fouling the plugs not inmediately though, as the motor doesn't count with an installed hour meter can't possibly know at how many run hours the plugs are being fouled. Cylinder compression is 180 PSI at both cylinders. Will install a new head gasket with a thin even coat of Permatex Aviation, seal the block and that's it. This is the only 18 HP giving those problems where the rest lubed with a high quality 2 stroke TC-W3 oil and run at constant middle to max wot rpm range are not having that sort of issues whatsoever.

Happy Boating​

 

[Faztbullet]

Below is piston wash... If it was my customer I would richen up the idle circuit a tad and maybe substitute a higher degree t-stat, might not be a Tohatsu one.

 

[Sea Rider]

In previous 2 strokes, 2 cylinder18 HP motors restorations have always found the upper piston to have carboned up more than the lower one and that issue seems to happen in many non Tohatsu motor brands. The posted pic seems corresponds to a 3 cylinder motor, if so, not valid for comparison purposes against a 2 stroke 2 cylinder motor. A 3 cylinder motor will always carbon up one piston than the other 2 whether being the upper, middle or lower one. The motor has 120 PSI even compression on both cylinders, wrongly stated having 180 which it's impossible to achieve.

Why would you richen up the idle when the motor is rarely run at idle rpm, usually passing half throttle which works with a fixed non adjustable speed jet.The installed OEM thermo is working right on, can feel the cold/warm cycling going on when placing your hand at middle leg's back.

Other issue that could affect the motor fouling plugs is that operator doesn't warm up the motor, starts it and revs it up, multiply that scenario by 15-20 times per day per month...

Happy Boating​

 

[Faztbullet]

The pistons/pic are for reference showing wash pattern and are not from a 3 cylinder motor. You stated a beginning of post it is ran at low to medium speeds . This is usually the transition range of crossover in carb which stoichiometric mix is affected. Also your hand is not a good tester for temp.

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[racerone]

Plug fouling ??----Maybe there is something else going on.-----Plugs are well engineered / specified for a motor.------Plugs rarely fouls on modern engines.-----Only the operator who THINKS that plugs are fouled.

 

[Sea Rider]

There's too many issues associated to this notor :
Runs low to medium throttle range - Powers a large medium light boat - Prop has not been maximized, surely revving way under the min lugging wot rpm factory stated when transporting many boaters to their respective anchored boats - The motor is never warmed up by the operator, the manufacturer advises to be warmed up for at least 2 minutes when first cold starts or consecutive cold restarts - Low 84 fuel octane with crappy 2 strokes TC-W3 oil mixed to 50:1 or tad over - NKG Spark plugs were found to be counterfeit ones. When the combustion chamber and exhaust head are finally cleaned up will install a new head gasket and pass on this one. Dislike the use of recreational motors which loves to rev high when are constantly being used for crappy slow operations which were not intended for...

Happy Boating

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