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First time top end help

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Hi,

I picked up a 2011 YZ125 yesterday, this is my first 2 stroke so replacing/checking a top end is entirely new to me so I am not sure if this is normal so I would like some advice.

Just some background on the bike, before fiddling with the engine the bike sat for 6 months+ and was only just started the first time yesterday. The previous owner said he had a mix of 15:1 in the tank when he started it on the day I picked it up. The carb needed a big clean so I did not give it any big squirts but it did pull hard when I gave it a quick ride around my house and was starting on the 1st kick cold.

After taking the head off and moving the piston to the bottom of the stroke, I can see nor feel any scrapes in the cylinder wall however there is slight discolorization(see image pic 3) in certain areas. What is the cause of this?

Now what I am most interested in getting an opinion on is what looks like 2 little indents or areas that have been rounded off/pushed in near each port. (see image pic 2) These little indents as you can see from 'pic 1/2' are basically evenly spread across all the ports. Is this normal?

Additionally, between each of the port holes the finish is pretty rough with one of them pretty sharp, is this something that should be rounded off or just left?

Thanks for your help.
 

pic2.jpg

pic3.jpg

pic5.jpg

Edited by Destero

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Want the bike to be great and last?

Get a manual for it, and read it. 

Pull the entire top end off, and remove all the studs, PV, etc, and send it off for re-plating and new piston. Clean up the head, order a new OEM gasket kit, carb kit, a few air filters, and re-assemble when you get it all back.

Looks like it got pretty hot from lack of oil in the mix. Bet the underside of the piston looks about as cooked as the sides of the jug.

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The Yamaha YZ125 owner's manual recommends 30:1 with a minimum of 95 RON octane (equivalent to pump 91 octane in north america)

It also suggests 15:1 during initial break-in.

Edited by mlatour

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1 minute ago, mlatour said:

The Yamaha YZ125 owner's manual recommends 30:1 with a minimum of 95 RON octane (equivalent to pump 91 octane in north america)

They also suggest 15: 1 for the first tankful / initial break-in.

oh sh*t, my bad I havent looked at it in a while

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