Thanks in advance for any ideas.

Purchased the bike several months back. Previous owner had just replaced the piston some 3 months earlier (or so he said).

I have the old piston and it shows the same signs that this one does. Blowby, carbon buildup, and some abrasions on the exhaust side. Head is loaded with carbon more towards the exhaust side. No movement in the crank

PV is very dirty, head and cylinder did not seem to be torqued to specs, when I bought it the PO had run it with a bad filter. Outer layer had come off or removed but continued to run it that way.

It seemed to run fine. Smoked & bogged while cold but once wamed up ran fine.

Lucas semi-synthetic oil, 40-50:1

Bike is very seldom run wot, mostly mid to lower range.

Live in the dominican republic at sea level with average temps of 80-90.

Jetting is standard, main 160, pilot 35, needle is set in the middle (3) don't know what needle but I assume it is stock.

Getting ready to drop a new piston in and clean up and hone the cylinder.

I would like to avoid this problem in the future. Any suggestions as to what could be the cause and how to resolve it.

Once again, thanks in advance for your help.

Can you catch a fingernail on the exhaust side abrasions?

What quality of gasoline is available there? Carbon buildup on the dome suggests lean jetting. Starnge that there is no carbon on one side of the head, maybe the spark arrestor is plugged up?

Do I see rust spots on the crank?

SkiDaddy,

Thanks for the info. The abrasions on the piston and the cylinder are minor.

I can feel them but it would not stop my nail. I am confident they will come off the cylinder easily.

I use only premium which gives me about 93 octane or so I think.

I had thought about the lean jetting issue but was not sure where in spectrum it would be.

Spark arrestor is not the issue as it does have one. I just repacked the silencer no too long ago. It was definitely trashed. Long overdue. Could that have added to a lean condtion?

In regards to the rust on I am not sure. I saw spots on the crank but did not know if there were rust. The were small dots in a couple of small clusters. What does that indicate? I will check again tomorrow.

Thanks for you help

Hi man, let me write JUST my opinion on this matter.

Well:

1) read this:
http://www.eric-gorr...bleshooting.pdf

2) read this:
http://www.eric-gorr...performance.pdf

3) forget KTM oil mixing recommendation! Just forget it! High-perf 250 2T = 1:33 or more. 1:50 is nonsense, 1:40 also.

4) check all settings related to charge: carb jetting (stock jets?, what is recommendation from pro circuit / FMF tunners ► see their sites / jetting support!), check all critical places along charge route: all around rad valve and carb boot, crankshaft sealing rings (especially under magneto ► dry conditions)... all must be pretty airtight so as to protect to air sucking.

5) btw KTM is european manufacturer... I am from Czech republic nad standard is 95 octane fuel. Better is 98 or 100 octane fuel here. But it should not be you problem.

6) Jesus ....... I have just read semi - synthetic oil ? ... oh...! forget it, full synthetic oil only .. .the reason why is your PW dirty. It must be pretty clean.

7) check spark plug heat range.......

7A) carbon and its amount concerns oil! There are oils which produce no carbon. But type of your carbon is unacceptable (see Gorr).

8) how about bottom of piston (in cavity)? brown colour? ► if so, high temperatur, thermal problem ► lean charge mentioned above

8) .. in my opinion your problem is simple: bad and small amount of oil in mixture. How about intake side of piston? Worn? There is lot of investigation targets for sorting out your problem.

Good luck!

btw in my opinion nicasil is done: need to replate cylinder and new piston assy

3) forget KTM oil mixing recommendation! Just forget it! High-perf 250 2T = 1:33 or more. 1:50 is nonsense, 1:40 also.


Ahhh What? Modern oil...... U shouldn't have to mix like its the 1970's. But I guess thats why its Called YOUR bike and NOT MINE.

... what to say...

1) I do not see your opinion on this problem which would be more usefull

2) I have had the chance of knowing and speaking with people who competed in the past (125 and 250 2T) and they say If you do not want to have the trouble, 1:33 is a start point.

1:50, 1:60 etc (ktm ratios) ... simple way how to meet legislation...

rm_killer, on 17 February 2012 - 09:54 AM, said:

Dude you are rediculous. 32:1 is a fine ratio, but depending on what you're doing with the bike, it can be too much oil. Plain and simple. If you are going to be running wide open most of the time, then yes, run it pig rich @ 32:1.. If you are going to be doing offroad with it, where you are well under half throttle most of the time, 40:1 or 50:1 are great.

I do agree that full-synthetic oil is the way to go- it will keep your powervavles much cleaner.

Don't go spewing your stupid opinions like they are proven fact.. some poor chump might actually listen to you.

thanks guys for the info. Had to get the cylinder and piston from the states.

Also, while I am at it decided to redo the bottom end. Crank and bearings.

Still waiting on everything.

Thanks