Can you read my piston? Pics!

Ok, So I bought this bike from a guy who lived at around 8000ft. I am at 5500 ft. I rode it twice at local motocross tracks, then decided to tear it down to baseline all the maintenance. I have no idea when this was ever done, and am beginning to wonder if this was the 1st top end done on this 2005 bike? I think this looks bad??

The jetting is 172 main, and a 45 pilot. I would think that would be a little rich for 5500 feet, any opinions by looking at the head?

Spark-plug is black, but the center deep electrode is brown.

The cylinder looked fine, with crosshatching still very visible. No scores or anything that would catch my fingernail.

Any opinions? Facts? Laughs?

Thanks in advance!

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holy richness batman

What premix?

Piston looks too lean...but I bet the bike was run with a Spark Arrestor in the trails a lot.

Looks good to me...no wash or major carbon build up. Very little blow by too...

The bike is set up for the trails, rekluse, fmf turbine core, etc. I am currently going to use it as a track bike, with an occasional trail day if a friend wants to use it. I use maxima super M, but I have no idea what the previous owner ran.

Looks good to me...no wash or major carbon build up. Very little blow by too...

Don't you want just a little piston wash around the outside diameter of piston?

The bike is set up for the trails, rekluse, fmf turbine core, etc. I am currently going to use it as a track bike, with an occasional trail day if a friend wants to use it. I use maxima super M, but I have no idea what the previous owner ran.

It should look a lot better with Super-m @32:1 and no sparky.....Looks like he ran Golden Spectro.

I would say a touch lean for mx track work or a fast rider , but other than that it looks good

Don't you want just a little piston wash around the outside diameter of piston?

It should look a lot better with Super-m @32:1 and no sparky.....Looks like he ran Golden Spectro.

If your running on the track I would fatten the main up by 1 or 2 numbers but if your just sticking to trails I would leave it as your elevation drop will cause it to run richer anyways

That is a huge hot spot under the crown. Either needs a bigger main, or the ignition is too advanced and or it was detonating. Otherwise it doesnt look kike there's much time on it

so richen the main and maybe lean the pilot? Where is all the black on the sparkplug and spooge in the powervalve coming from?

I'd ride with the jetting it has now before making changes. No telling whats been in it before. Some one could have experimented with way smaller main jet at one time

Edited by adam728

so richen the main and maybe lean the pilot? Where is all the black on the sparkplug and spooge in the powervalve coming from?

I wouldnt lean the pilot, just go up one or two on the main. If anything, I would go richer on the pilot if need be....

Powervalves could be as simple as the oil used....

If your running on the track I would fatten the main up by 1 or 2 numbers but if your just sticking to trails I would leave it as your elevation drop will cause it to run richer anyways

Elevation drop will cause it to run leaner not richer because air density increases.

Elevation drop will cause it to run leaner not richer because air density increases.

You sure? I thought it was the other way around....

so richen the main and maybe lean the pilot? Where is all the black on the sparkplug and spooge in the powervalve coming from?

175 main and leave all else alone.

All the black is from a combination of trail riding, spark arrestor, and dirty premix oil.

You sure? I thought it was the other way around....

Lower elevation has greater air density and requires more fuel - bigger jets.

YZ250VJetting.jpg

I will try riding it with the current jetting. I put the top end back together with a new wiseco piston, new boyeson power reeds, new plug, new dep pipe, hour meter etc.

Would it be worth it to use a stock silencer in lieu of the fmf turbine core I have now? How much would that affect jetting? Will the DEP affect it? (there was a dented / crushed at the header "Bills" pipe on there before.)

Dropping the SA and riding MX and you are hesitant to go richer on the main.....What do you think will happen? The bike will be faster with a richer main. (If you are too lean now)

I thought it was running rich now? is a clean head indicative of rich or lean jetting? I also have a mostly black spark plug with only the very inside (deep on the electrode) area brownish colored.

Do some research on piston wash. You want small clean areas on the top of your piston where the transfer ports are. Your piston looks slightly lean.

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