Super Jet Help with piston wash

[Yami-Rider]

I have about 1 season on these pistons, the plugs look ok to me, but i dont seem to have any carbon build-up on the pistons, Does it take many hours of run time to get piston wash or ?... I know this has been covered before, but i couldn't find a piston that looked like mine do.

They are very clean, very little color




Left - Rear (little rich?) Right - Front (Just right?)




728cc 61x/62t, Mild port/polish, Stock 38s, B-pipe, X-metal box, Fiber Reeds, 35cc 185psi head, BR8ES plugs, Adjustable RPM CDI.

Stock Dual SBN 38's
135 Main
75 Pilot
44 PSI Pop-off
Rear Carb - 48 PSI Pop-Off - already lowered it to 44psi to match front carb.
Almost 1 turn out - Low speed
1 1/4 turns - High Speed

I also noticed my center linkage between the carbs was a little out of adjustment, rear carb wasnt opening as far as the front carb.

 

[Tyrant1919]

My 850 pistons look as clean as a whistle too... I'd like to know too. Hell my first 850 motor with 550~ gallons of gas through it was awesomely clean like that. But having a slight carbon buildup on my pistons is at the very bottom of my list of things to worry about.

 

[hink320]

The pistons are most likely so clean due to water ingestion, it basically steam cleans the pistons.

 

[restosud]

or running rich.

 

[Yami-Rider]

The pistons are most likely so clean due to water ingestion, it basically steam cleans the pistons.

Didnt know that, my engine drink about as much water as it does gas lol.

or running rich.

That's what i was thinkin at first, but the front plug looks so good.

 

[sxipro02]

Plugs (mainly the one on the right) looks perfect. I agree, the pistons look like they are seeing some water.

 

[IS0LD0UT]

I thought I read in another post about some of the synthetic oils not leaving carbon.

 

[Tyrant1919]

<<< Red-line ???

 

[Jakobi86]

It's from being rich. Raw fuel washes top of pistons off to the point of being clean. Plugs look good because the richness has the same effect. Water ingestion won't mix with gas/oil ratio and def won't clean a thing. I bore scope my engine in my snowmobile and come up with a piston wash on the clean side, meaning rich. Motors last when they get fed their fuel, Make more power on less fuel and cost way more money on even less fuel... My .02, leave it alone if your happy with the way it runs


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[kevbo]

It is common to see dark plugs and clean pistons in standups that arent getting much full throttle use.

 

[Jakobi86]

Ideal jetting and piston wash would be black top pistons with knife edged tear drop shape clean (shinny) areas by the transfer ports that extend about 3/8 in towards the middle of the piston with plugs that are dry and cardboard to chocolate colored brown


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[ajmps1]

Looks like water intrusion or too rich. Hows it run? Do you have another ski to compare to?

 

[Yami-Rider]

Looks like water intrusion or too rich. Hows it run? Do you have another ski to compare to?

Runs pretty good, towards the end of the season I could tell my tuning was getting a little off. Compare it to? I have about 16 ski's sitting at my shop right now, I personally own two SJ. I have seen ski piston's that had color before, if that's what you meant?


There's a lot of good points that have been brought up. I just rebuilt my carb's, Ill tune a little and run it.

 

[High Speed Industries]

 

[myusername2013]

Useful chart.

Sent from my Galaxy s4

 

[Yami-Rider]

It's from being rich. Raw fuel washes top of pistons off to the point of being clean. Plugs look good because the richness has the same effect.

Forgot to comment on this... Your logic makes since on the pistons, but doesn't on the plug comment IMO. I put new plugs in and they turn coco brown that should mean im close to the correct tuning, too rich turns them black/oily wet.

 

[Jakobi86]

Black/oily wet is usually from oil fouling, not fuel. The reason there are shiny areas on the piston in the above pictures is because the fuel cleans the carbon off, hence the reason why the one that is said to be jetted too rich, is the cleanest. If you look at the plug end, the metal ring portion at the bottom ( the threaded part) you can see it's shiny and clean. The porcelain however is able to take a "stain" from the additives in the fuel along with oil. No matter how much you try, the metal won't stain, but the porcelain will and that's the color you get. Plug reading is an art and I am in no way a genius at it, but being that I must know at all times what's going on in my two strokes, I've put a great deal of time and research into learning what does what and why it looks the way it does.


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[Jakobi86]

Also as stated above your condition could be from not a whole lot of full throttle use and the fact that these float-less carbs are tuned for a compromise at best across the enitre fuel circuit, couple that with generally warm weather riding and the fact that I tend to believe these carbs are overjetted to begin with, leads me to think tha majority of the time these engines are running on the rich side... This is not to say burndowns don't happen, lean conditions aren't ever present or etc... If you get what I'm saying, I know it's a lot lol. Like I said, if your happy with the way it performs, run it. Better that way than the other extreme


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[Jyzmbe]

My builder told me when everything is clean like that your engine is being over cooled and not reaching operating tempature


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[kevbo]

My builder told me when everything is clean like that your engine is being over cooled and not reaching operating tempature


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Spotless pistons are mostly a standup thing. They spend a lot of time at part power and must be tuned very rich in this range for good response. A peaked out sitdown will have clean plugs and dirty pistons.