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Piston Analysis

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Hi All,

Please can the experts on here give me thier opinion on how my bike is running from the following piston pics i took while having a quick examine of the head gasket

Piston has 4 hours on it since rebuild with cylinder replate also

ImageUploadedByThumper Talk1398045566.500433.jpgImageUploadedByThumper Talk1398045580.869496.jpg

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I may be wrong but I believe if it was rich the piston would be clean on top not carboned up.

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Did you do the top end or did you buy it like that? That looks like more than 4 hours. Open up the carb and tell us what your jetting is, including the needle.

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Did you do the top end or did you buy it like that? That looks like more than 4 hours. 

:thumbsup:

 

If top end is not done by TS I would take the whole cylinder off for having a better look at the piston... That piston could very well on its retirement days. :devil:

Edited by KTMfinrider

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Did you do the top end or did you buy it like that? That looks like more than 4 hours. Open up the carb and tell us what your jetting is, including the needle.

I had the shop do it and installed an hour meter at the same time, what would cause a piston with only four hours to look worn out already?

I think my jetting is

208 main

45/48 pilot

Nozh/3rd clip

1.5 turns out

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What size, model, and year is your bike? Aftermarket pipe, silencer? Approximate riding elevation? We will need these to determine your jetting.

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There are a lot of factors that determine these things.  Your premix ratio should be chosen in advance, then you jet your bike according to weather conditions and premix ratio. 

 

My piston had 125 hours on it, there wasn't any carbon crusted on top when I changed it out.  I jet my bike to the specs in the manual, run 50:1 mixture of Amsoil Dominator.  That's my baseline, but I've given thought to richening the mixture and richening the jetting too to compensate.  There are a lot of educated posts about the bike running more powerfully with a larger charge of fuel.

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I've never had a 150, but was looking at the jetting forum on KTMTALK. Seems different year bikes ,people used different jetting.I never saw anyone have a main jet that big, and most used smaller pilots too. What year is yours? Do you have the manual? Most say the manual is a pretty good jetting guide.

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Most people don’t open up their top end at 4 hours just for fun. So what was happening/going on that made you take a look at the piston?

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The reason i have used that jetting is the carb table jetting wasnt right for where i live/climate/type of track (leeds,uk) all my local shops told me this is what they advise me to run and my throttle response is just right, still on the rich side but I prefer it a little than a little lean

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I may be wrong but I believe if it was rich the piston would be clean on top not carboned up.

Rich mixtures carry lots of fresh oil to the cylinder head, where it gets burned and leaves carbon residue. Lean mixtures don't allow oil to burn on the head because all of the fuel combusts entirely.

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Rich mixtures carry lots of fresh oil to the cylinder head, where it gets burned and leaves carbon residue. Lean mixtures don't allow oil to burn on the head because all of the fuel combusts entirely.

Rich= piston wash

Piston wash = clean piston crown

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If it's running the way you like it, I say keep going with what you've got. You'll just have to clean the top end more often, but that's no big deal. Since you've found no problems, I would venture to say the milky overflow was condensation,or water from washing or a water hole.

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Interesting . If an excessively rich mixture would cause piston wash and a clean piston top , would this not also not result in either a dark plug and or spooge  ?

The reason why I ask is because I recently installed a 300SX top end in my 250 SX . I've now have 5 hours on the new motor . I am running fairly rich jetting and there is zero smoke , zero spooge and the piston top looks brand new clean . The inside of the silencer is completely dry and the plug is brown . This is with a 170 MJ .

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