Posts
32
Joined
12/28/2024
Location
Modesto, CA
US
Bought this 2005 YZ250, fires up first kick every time, runs really good. This motor just sounds really loud, the guy did say it might need a top end soon. Also the bike runs really crisp has spooge coming out of the pipe, but when looking at the plug the insulator is white and the surface of the plug is black and covered in carbon. Not sure if it’s from running 91 octane. The bike is all stock other than a Fmf pipe.
Sounds good. I liked to run my idle a touch higher personally - keeps it from having that stumbly sound like it’s loading up
Thanks for the input, what would you say the cause of the white insulator but Black plug surface? It’s weird cause it’s really crisp with a clean transition from 1/4-1/2 throttle into the power band, but I noticed when full throttle the power seems a bit dull is the best way to put it, after just getting in the power band at full throttle is already feels like it wants to go up another gear. It seems like the band is really short and lacking power at high rpm.
What oil are you using and at what ratio? You may be running a little rich in the main. What is the main jet, elevation, and temp around you?
Also, if you're technical enough for it, adjusting the timing on the Yamaha's makes a really big difference. I was about to buy pipes and heads etc for mine but decided to get timing adjusted. I went from the stock -7 degrees to -3 degres and it gave the bike so much more of a steady and usable upper that didnt sign off so quick. I mean it transformed the bike. Single biggest change I ever made to it. Please double check those numbers first and verify your own!
I Don’t have any of the nessasary tools to change the timing. I’m running 32:1 Formula K2 with 180 Main, 50 pilot, and 3 clip stock needle. At sea level, going to mainly be riding in weather from 30-80F.
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Try the 178 potentially. I would also see about some SuperM at 32:1. Obviously one at a time but try that. I would be curious to see how a little leaner jet affects the top.
I have a timing tool setup I would potentially sell. I don't have a price in mind - throw a price out there lol what is it worth to you?
I had just changed it to 180 because 178 had a hesitation getting into the power band. The 180 fixed that hesitation but the powerband seems short now
It’s good, I’ll probably pick up a new one from my local shop.
Interesting. I am going to bow out at this point as I am honestly not competent enough to continue the help bahahaha. I limped through jetting setup in the past and had alot of guys on thumpertalk help me. I'm straight up bad lol. Keep it the same, work the timing. See what that does. Report back too!!
I see your pipe mounts are all broken. That will lead to a LOT of vibration and extra noise.
Good to replace those along with your exhaust springs and o'rings. Otherwise, this bike sounds SOLID.
That upper pipe mount bolt was missing I got a new bolt in it, both mounts are good. It’s just missing an exhaust spring and bad orings, also just found a crack in the pipe that needs to be welded. Only like an inch crack.
My 2015 model that I picked up nearly a year ago ran great and had a little extra noise to it compared to my buddy's brand new '24 and my other friend's '21.
Went to do a top end just because the previous owner didn't know the hours on it. Found the lower half of the piston skirt (intake side) was broken off, with chunks sitting down in the crankcase. This is the reason to check these things.
Ended up splitting the cases just to be safe. Also found the shift stopper ball bearing's outer race had cracked (hadn't come apart yet -- replaced with the updated 2016+ version that doesn't use a ball bearing at all. Definitely check this on yours.). Now I know the engine really well and have the peace of mind that everything's sealed up well and nothing's just hanging on by a thread.
A compression test is usually an easy way to tell of the freshness of the top end. As the rings wear down, and the bore wears down the compression will start to drop. For a fresh 250 over 190 is a healthy engine. You can run them when they get lower than that, but when it drops below 140~ish, it needs some attention. Some guys run those hour meters, but that doesn't tell you how hard the engine has been run.
My 09 was jetted very well and ran great but always on the verge of detonation with 91 octane. I ended up mixing C12 with pump fuel and it cleared that up.
Could be crank seals
The motor was sadly not solid
Post a reply to: First time owning 250 2 stroke, dose this sound normal?