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300exc 1998 seized for 2nd time in a year

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hi evreyone. concerned for this bike now because in jan this year the bike seized and basically there was light scoring down one side of piston which had broke the rings but the piston didint look bad actually. afeter a top end rebuild, re plate and wossner piston, ive had bike out a few times this year about 45 hours on a wossner piston.

when i went out last week the bike was pinking badly. ive moved the clip to the middle as it was on the leanest setting. pinking had now gone and was running very well although it would not rev right out but it had that much torque it wasnt an issue.

yesterday i went up a little muddy hill in 2nd gear on about half throttle and it cut out and you couldnt move kick start.. ive stripped it and the top of piston round the edge as just broke up causing major scoring into barrel. i mix at 50-1 . is there something ive done wrong or has piston done to many hours or did the pinking cause the damage.?

ps i did notice the engine was very noisy but i was told on here by lots of people they are quite noisy anyway. i only had engine out bout 3 months ago to do crank bearings and everything looked ok.

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Pinging is usually caused by to low of grade of fuel. What grade were you running? Has anything been done to the engine that would raise the compression a lot?

You mention the needle but didn't say what main jet it has. Why don't you list the main and needle, and any other settings so we can help you.

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mix it to 32:! problems sovled....ktms run lean when they are at open throttle places so i run mine rich, i dont get very much spooge but it is very reliable ive never fauled a plug and it runs like new.....with my whole motor just being rebuilt it is happy the way i have it set up/

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mix it to 32:! problems sovled....ktms run lean when they are at open throttle places so i run mine rich, i dont get very much spooge but it is very reliable ive never fauled a plug and it runs like new.....with my whole motor just being rebuilt it is happy the way i have it set up/

This post is just so full of fail.:bonk:

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Sounds like the jetting is too lean so far... and just going from 50/1 to 32 /1 will NOT fix that problem.. I also use 50/1 mix but I do have to re jet each fall and spring

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ive found the bearings in conrod have callapsed. the conrod will move but with alot of force. could this have caused it? the piston as lots of marks on top round the edge as if you dropped about 20 tiny metal ball bearings in and let them bounce around. ill try and get a pic but my iphone as been sent for repair so im using a very old phone with no camera.

also lads ive not got a clue with all this jetting side of things. people talk about it on here and they loose me on the first sentence.as far i can remember its running the standard size jets. its on the middle setting on the needle and screw is 1 and half turns out

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Your pinging noise was obviously the bearings bouncing around in the cylinder.

Did the lower bearing go or the top one?

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lower bearing went. the pinking was happening and i stripped and had a look at piston but no damage so i put back together and it seized after about an hour of running

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I run 100:1 in my 125SX lately and runs like a scalded dog!

I have also used only 100:1 in mt 1100cc Kawi jetski for 10 years

never oner failure.

Quality of oil sure makes a difference in a 2 smoke

Javier

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mix it to 32:! problems sovled....ktms run lean when they are at open throttle places so i run mine rich, i dont get very much spooge but it is very reliable ive never fauled a plug and it runs like new.....with my whole motor just being rebuilt it is happy the way i have it set up/

Better yet run it 16:1.. I too run at 100:1 for the last 5 years..

To the OP I suspect something else is goin on inside your engine.. If the edge of the piston is broke off on the top then somethjing was probly in there that souldn't have been.. Without seeing it it is hard to know. Could be something came out of the lower end from the first failure.

Edited by zilla

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Better yet run it 16:1.. I too run at 100:1 for the last 5 years..

To the OP I suspect something else is goin on inside your engine.. If the edge of the piston is broke off on the top then somethjing was probly in there that souldn't have been.. Without seeing it it is hard to know

Looked to me as if the chamber just overheated and the aluminum started melting, lean jetting or also lean gas to oil mix will do it also like 16:1

More oil in a gallon of gas is less gas in the ratio mix.

Will have pics soon of a KX250 that melted down yesterday right before we got home. Not my bike! The 250 was running gas station 2cycle oil mixed at 40:1

Javier

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