Identifying the jet needle on my 2000 YZ125

minorgod · Oct 11, 2009

Greetings,
I'm new to motorcycle maintenance and recently bought a used YZ125. It runs pretty well with a new spark plug, but is constantly fouling the plugs and it doesn't like to idle for very long without stalling. Also, it was very sputtery in the middle of the power band particularly in 2nd and 3rd gears. The bike will keep starting fine once it's warmed up, but if it sits overnight it won't start again without a fresh plug or a LOT of effort. After reading the maintenance manual, I adjusted my pilot air screw to about 3 turns out and that seemed to smooth out the sputtering problem, the idling problem, and it seems to have helped the plug fouling a tiny bit, but I'm still fouling them after only 30 minutes of riding. I do seem to get more power from my engine after adjusting that pilot air screw, and the bike really seems to run great now other than the plugs fouling every time I ride. So last night I lowered my main jet needle by 1 notch and I'm going to take it for a test this afternoon and see if that helped. I'm also thinking that I might need to go to a hotter spark plug or maybe change the main jet needle to something slightly larger? I called the dealer to see if he could identify my current jet needle by the numbers (6CHY53-75) and he said it sounds like an aftermarket jet needle. Those numbers don't correspond to any of the standard sizes I've seen in the manuals, but it seems like the numbers on the needle suggest that this needle will give me a very rich mix and if changing my current needle position doesn't do the trick then maybe I should step up a size or two? Any suggestions? Anyone know where my current 6CHY53-75 needle might have come from?

mathd · Oct 12, 2009

The needle is probably from a jetting kit since it is supposatly aftermarket.
If it is too rich and flood of fuel when it sit over night then.
I would check the float level, can cause all the jetting to go rich.
Then the needle valve set could throw the jetting off if not sealing properly.

also, make sure the gaz cup close correctly and do not cause the bike to flood when it sit.

Otherwise you will have to jet it.
Before jetting it i also check for the reed valve, this will make a bike hard to start and run more rich, if they are to be replaced. Also make sure the top end is not going.

For the jetting there is great guides on this forum. concerning the needle part of it. If you are at the extent of it's adjustment and still need to go leaner on the needle(or richer depend of case) then yes, you will have to change the needle.

For the aftermarket needle/kit, this is a sector i have a lack of knowledges in so i cannot comment.

minorgod · Oct 12, 2009

mathd said:
The needle is probably from a jetting kit since it is supposatly aftermarket...

Thanks for the reply! It sounds like I'll need to pull the carburetor no matter what. When I lowered my needle I must have done something bad to the throttle cable because now I have no play in my throttle even after adjusting it to be as loose as possible. This seems to cause my engine to idle REALLY fast and sometimes it even revs up to to high rpm and I can only stop it by putting it in gear so it can't race so high. I thought my float was sticking or something, but then realized it was my throttle cable. I made it as loose as possible by the adjustment screw on my handlebars, but still can't get enough slack to keep the engine from idling too high. The idle speed adjustment screw doesn't seem to have much if any effect so I think now I need to fix the throttle cable to give it some more slack. I wonder if this is a common problem when changing the jet needle clip position.

mathd · Oct 12, 2009

minorgod said:
Thanks for the reply! It sounds like I'll need to pull the carburetor no matter what. When I lowered my needle I must have done something bad to the throttle cable because now I have no play in my throttle even after adjusting it to be as loose as possible. This seems to cause my engine to idle REALLY fast and sometimes it even revs up to to high rpm and I can only stop it by putting it in gear so it can't race so high. I thought my float was sticking or something, but then realized it was my throttle cable. I made it as loose as possible by the adjustment screw on my handlebars, but still can't get enough slack to keep the engine from idling too high. The idle speed adjustment screw doesn't seem to have much if any effect so I think now I need to fix the throttle cable to give it some more slack. I wonder if this is a common problem when changing the jet needle clip position.

This happened on my yz125 98 this summer while making needle adjustment change.
Its a little error i did too but really easy to fix.
Make sure the throttle cable end is assembled correctly into it's holder inside the throttle valve. If it is not set correctly in the notch it will hold but also it will remove slack from the throttle cable causing this kind problem. This is what happened on mine.

If it is assembled correctly, you should have the same throttle cabbe adjustment as before(no adjustment needed). Usually it should have some freeplay(see manual for spec)

minorgod · Oct 12, 2009

mathd said:
This happened on my yz125 98 this summer while making needle adjustment change.
Its a little error i did too but really easy to fix.
Make sure the throttle cable end is assembled correctly into it's holder inside the throttle valve. If it is not set correctly in the notch it will hold but also it will remove slack from the throttle cable causing this kind problem. This is what happened on mine.

If it is assembled correctly, you should have the same throttle cabbe adjustment as before(no adjustment needed). Usually it should have some freeplay(see manual for spec)

I was thinking it might be something like that. It's such a pain to get the throttle cable into the notch while compressing the spring. I'll give it another try next weekend when I have time to pull the top off the carburetor again. The good news is that changing the needle position definitely seems to have helped the problem of fouling the spark plug. I rode all day yesterday and then checked my plug and the fouling prob is almost gone..still a tiny bit too rich. Just a little more tweaking should do it, but I'm afraid I may still need a bigger needle when all is said and done.

Thanks again, your comments are very helpful!

motodr9 · Oct 12, 2009

The stock needle for your bike is a 6DHY53-75 part# 275-14116-J1. Be careful when routing the throttle cable and ensure slide and needle assembly is correct. A stuck throttle is bad, and usually happens at the worst possible time.

Also check your bike for a recall on the throttle assembly (throttle cable guide wheel). Call your Yamaha dealer and give them your VIN#.
However, I am a little concerned that your dealer couldn't ID your current needle, those are Yamaha codes.

minorgod · Oct 12, 2009

motodr9 said:
The stock needle for your bike is a 6DHY53-75 part# 275-14116-J1...

More awesome info. Thanks!

Matt90GT · Oct 13, 2009

you already said your problem.

your air screw should be between 1.5-2.5 turns out. You need to go smaller on the pilot.

mathd · Oct 14, 2009

Matt90GT said:
you already said your problem.

your air screw should be between 1.5-2.5 turns out. You need to go smaller on the pilot.

Yeah, he need to go smaller(or jet correctly for the pilot circuit not just follow factory spec for number of turn if this is what he did"and i really recommend to learn to jet correctly, lot of info in this forum") but i dont think that is the high idle problem since he mention that the problem started after making needle setting adjustment + the cable adjustment lost its freeplay after that needle adjustment. He also said that after the air screw adjustment made the bike idle better so i suspect more other thing first thant the pilot circuit.

jayhedrick · Oct 14, 2009

Make sure you run the hell out of it when riding... This happens with a lot of new 2stroke riders... Not running it hard will cause a 2stroke to foul plugs left and right... Also before trying 2 start it you can turn the gas on and lean the bike over and let a little has leak out then try starting it... When it starts up make sure you warm it up 2 prevent another fouled plug.... Just my 2 cents

Identifying the jet needle on my 2000 YZ125

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