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maintenance Yz85 03 running problems

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Hi, brand new to this forum so excuse me if this is in the wrong section!

We got a 2002/03 (unsure), yz85 a couple of months ago. Very few issues at the start, ran perfect. 

In the past two months the bike has been very temperamental. It was idling very high when it started but alot of the time it wouldnt even start. Was making very throaty, burpy kind of noises, especially with a bit of a throttle twise to try and get it going. So, after pulling the carb to bits, cleaning all of the jets, itd run once well, then do the same thing again. We repeated this process 4/5 times to date. We eventually routed the cause to a frayed intake boot causing a vacuum leak. So we replaced it. Good as new. For the first run.. kicked like a horse the first time we ran it after replacing the boot. 

Then today, she's back to her old self. Started fine earlier, and then just went throaty and started to die. Sounded like the plug wasn't firing. So took it out, checked. Nothing, check if there was power to the coil pack, got a spark, so cleaned the plug with a wire brush (b10eg, btw)

Away she goes again, for 2 minutes, and dies. Back to making throaty sounds again. 

The plug is working as of now.

The bike would start if the throttle was wide open but be very very throaty, burpy and rough. 

Carb was cleaned earlier before this. (Today) 


That's all the detail I can give, any questions feel free to ask me. 

I've given up on it as I'm all out of ideas. 

There was a bit of black oily stuff leaking out of the exhaust as well, only noticed as I was finishing up. 


Any help, ideas, suggestions are welcomed. I have a video of it but can't upload here.

Thanks in advance


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Something to think about in the future:  The spark plug is like a snapshot of what is going on inside your combustion chamber.  The only way most of us can see that in other words.  So when you ask about how to improve the way an engine is running,  including that will help.  Two strokes give off that residue you mention.  If it is excessive,  your engine is running too rich (fuel air mixture in this case is what I am referring to).   A very common way for that to happen on a rig that is higher in hours is that the float,  the float needle and gaskets need some attention.  So clean it and set it would be where I would start,  from the information given.  Jetting changes should only occur after you do that,  as the level determines a lot about how your brass is going to react. 

Edited by ossagp

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Apologies, forgot to include the colour. The plug is probably on the darker side of optimal. Comes out wet every time I check. I understand about plug colours and float heights but what I don't understand is how unpredictable the bike is. As I said, when we changed the intake boot, it kicked like a horse. the bike was flying, and this was before I adjusted the fuel/air mix via the pilot air screw. After that it was still flying, very little smoke coming out of the exhaust when warm. I don't get how it can go from running perfect to not running after a couple of days sitting up? I didn't mess with the float needle at all..

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On 4/11/2017 at 1:45 PM, Dylan Kilbride said:

Was making very throaty, burpy kind of noises, especially with a bit of a throttle twist

I agree with ossagp, sounds like a fuel problem. 

When I read the above quoted statement, the "throaty, burpy sound" that makes me think not enough fuel is getting to the cylinder (even though you say the plug is wet). The way I relate to the sound is when I am running the float bowl dry after a run. When it starts getting empty, you can twist the throttle and it does that throaty, burp sound. Like a bog.

What condition is the tank in? Is the fuel clean? 

If you are getting a good, strong consistent spark, and you don't have any air leaks, I would make sure the tank is clean, as well as the strainer/filter inside the tank. Good fuel lines and I would re-check the carb. If the float bowl is filling up and then sticking somehow, that would explain the "starving" sound.


Beyond that, I would start looking a little closer at electrical. 

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