this is a pic of a lean piston

this is a pic of a rich piston

this is a pic of a good piston. with a correct wash in proper state of tune. this is what you want to achieve.

I think you have lean and rich mixed up, double check your pictures and your posts...
I agree, Pic #3 looks right.

negative, pics are correct. the shiny areas are from fuel hittin the piston top.....not enough fuel, no shiny spots.

As the name "wash" implies, too much fuel and the carbon is washed off at the port windows.

I stand corrected..., thank-you Dr. Thumb. How'd ya get that name anyway?...??
I would feel much better if 'Mikadoo' confirmed this, though, he seems to know the most on this site and dootalk.
Cheers!!

I would say those are perfect examples too,other than the one that is good,i would like to see a bit more wash to leave the average person a little more leeway on a cold day,but yes those are perfect examples of jetting conditions

bear in mind that these are perfect text book examples. some engines are inherently more efficient than others. for example it is easier to get complete combustion in a little 125cc motocross bike than it is in the huge jug of an 800 or 1000cc twin. dont be alarmed if the results that you achieve are not exactly as illustrated. other uncontrollable factors like outside tempurature,barometric pressure,elevation,fuel quality,etc can affect your readings,without even touching any settings on the sled. personally for trail riding i would err on the side of caution and like to see a tiny bit more wash around the ports as well.

I stand corrected..., thank-you Dr. Thumb. How'd ya get that name anyway?...??
I would feel much better if 'Mikadoo' confirmed this, though, he seems to know the most on this site and dootalk.
Cheers!![/b]

Redlined I'm sure you meant no disrespect to Thumbdoctor.

Take Thumbdoctors words to the bank. They are good as gold when it comes to advise on snowmobile engines. :rolleyes:

My Yamaha phazer just burned a piston. Here it is. Jetting is 145 mains, 95 pilots and Boyesen reeds. It's a Parts Unlimited piston, .020 oversize, not OEM. It also has a single aftermarket pipe. Not sure what brand though. :dazed:

What do you guys think?

it definately is not to lean were you riding in warm weather?

Maybe a little oil lean?

I looks like the mixture is correct. Is there any other damage? Such as broken rings? Cylinder head damage?

Cold seizure.

Piston sized in the cylinder due to not warming it up, under sized bore, or both.

When the piston shows 4 spots of seizure like that, it means the piston swelled faster than the cylinder did. Common in a iron sleaved engine (like yours)

I just got it back together with a new piston. I hope it is not a bad crank seal. Have to split the cases to change them. I hope it's cold seizure. How long should you let a sled warm up before full throttle? Esp an air cooled one. Undersized bore sounds good. The guy who bored my cylinder seems to have done a lousy job.

I also went down to a 140 main with new Boyesen reeds on both cylinder. The thing it the right cylinder is fine, not burned at all. I hope we get some snow now so I can try it out and see if my rpms come up.

when i first read your post way back when i was in a hurry and didnt have time to post. i was gonna post that i didnt see any melting... the scuffs didnt strike me as real unusual but if they where in four spots it wasnt a burndown but rather a seizure. 145 to 140 isnt alot, and i cant tell by your pics really what the wash looks like and really that to is subject to the conditions and throttle opening/ length of time you were running it. i would getertogetter and progressivly make some longer and longer passes starting at 400' then 700' then 1000 ' each time checking the wash and BURN line on the plugs. i would really, really keep a open mind to the rpm problem lying in the clutching too. call it a gut feeling.

I got it running and just blipped the throttle for about 5 minutes. I'm trying to synch the carbs and now I have a plugged fitting into my right carb. :cussing: I don't know why this is. Can you take the head off and inspect the piston and reuse the gasket to check piston wash? EGT would be the way to go I spose. What are the optimum temps for EG? Air cooled sleds don't have a way to keep from getting TOO cold.

Too damn cold here to ride too and lame snow totals.... :bash:

i use a 15$ flexlite commonly sold at auto parts stores and stick it down the plug hole. with the piston at the bottom of the stroke you can see the whole top...ya have to sqint a little.

Does the injection system on your Yamaha mix the oil with the fuel in the carb float bowls?. I saw an older V max seize because the owner reduced the mains which also reduced the lubrication.

Does the injection system on your Yamaha mix the oil with the fuel in the carb float bowls?. I saw an older V max seize because the owner reduced the mains which also reduced the lubrication.[/b]

Nope. It's injected into the intake boots, center bottom. Looks like it just trickles down into the cylinder/piston. I might have to drill out the sync fitting to get it open. I'd really like to see if my changes will make the ole Phizzer rip, but the snow here is weak.


Nothing worse than subzero temps and little snow. :cussing: :confused: :bash: :(