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06 YZ 250 questions

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Recently my brother picked up an 06 250, great bike so far.  It runs good, starts easy, but SMOKES A LOT!


This weekend was the second ride, we had the chance to clean and jet the carb, repack the silencer, and change the trans oil.  The carb was rich imo, 50pj, 180 main with the stock needle (NE3J? 2nd pos down from top) in the stock position.  We threw in a 45 pilot, AS 1.5 out, 175 main and left the needle alone.  My brother is a lugger, so we figured that was a good starting point.


I expected a lot less splooge and smoke, and intially it was better, but after about 20 minutes it started to get bad again.  When we dumped the trans oil we got about 550cc's out, but since it was the original owner who had put it in who knows how much he had in there?  Splooge all over the swingarm, leaking out of the exhaust flange too.  The plan is to dump the oil again soon and measure what we get out.

Just like my last Yamaha (02), it drips splooge from the PV breather after every ride too.  I've never done a leak down test, but is that my best option?  Seems like jetting should be close enough for a baseline, or am I way off?  Any ideas??  The bike was "recently rebuilt", but does have good compression, runs great, and starts easy, just smokes, and loads up after 15 minutes of lugging.  Haven't fouled a plug yet.


Is the chassis the same, in respect to bolt patterns etc., from 02 on?  Or do all the mounting point change in 05 when they went to the aluminum frame?  Looking at sparky's, would like to buy used and expand the search if those years bolt up?


Thanks for any advice you have. 

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You can't really fine tune the jetting until you've confirmed that the crank seals are in good condition (leakdown test)

you must also confirm that the float / fuel level is set correctly in the carburetor.

plus, if you lug this MX race bike around, make sure you use a low flash point premix like Interceptor or Lucas (not some high temps 'racing' oil)


Moderate leaking from the YPVS breather hose is considered normal.

When the top end is due for a refresh, have the compression squish height corrected, that will make it run cleaner & crisper at lower rpms.

Edited by mlatour
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Running Amsoil Interceptor 32-1, he ran 1 gallon of 110 with 4 gallons of 93 pump at 32-1 in his 96 cr 250, was using that fuel up this weekend.  


I will do a search about the leak down test, will need to build a tester.  Thanks for the info.


In respect to squish, what is the desired dimension?  Does Yamaha offer different base gaskets like KTM, or does it involve machining the head?

Edited by poldies4

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