Idling and spark plugs...

[wjp]

Hi all,
being new to the sport I need some help here.
I've recently purchased a '99 Yam 125 WR. This aparantly is unique to France (where I'm currently working). Anyhow is a modification Yamaha France do - basically is a YZ thats been made road legal (as far as I can gather). Anyhow I digress..

When I brought the bike it won't idle at all without using the throttle. Not really knowing much I found the screw which is on the outside of the carbarater. When I turned it in the bike would then idle.
The problem that I have been experiencing is that if I let the bike idle for a short period (a couple of minuites) it wet fouls the spark plug. Also pretty much everything I try and use the bike after its been standing for a day I always wet foul the plug. I have to clean it at least 2-3 times before I can get the bike to start. Once it going , it runs well.

Have I done the right thing by altering this screw - what is it exactly - is it the air screw? How can I stop the bike from wet fouling the plugs when the biek is idling, or is this just a symptome of this bike? I read lots here about jetting but don't know anything about it.

Any thoughts or help is much appeciated.
Wayne

 

[yam 3]

I have a 00 yz250 us model and I have a plastic looking screw that adjusts the idle and another smaller brass screw that adjusts the air screw. I would turn the metal screw out 1 1/2 turns from fully in, and then adjust the idle. If it still fouls then you might go another 1/2 turn on the air screw, but you probably need a leaner pilot jet.
Before doing any of the above check the air filter to mnake sure it is clean as a dirty on will cause a rich condition.

 

[David Trustrum]

Once a plug fouls it may not recover properly. Out in the open it may spark well but in a combustion chamber may just foul up again.

Bikes are usually set up rich std. Turning the airscrew out will lean the mix a little but yeah try a 1 size smaller pilot jet & play with the airscrew to find the optimal position. If the bike dies when you crack the gas on (pilot controls idle to just open) then you have gone too far & wind the airscrew in a bit.

The idle speed screw has a spring behind it, is on the side of the carb & raises the slide. The air screw is back a bit & not quite flush with the surface.

Um, most performance 2 strokes don’t handle idling for too long as combustion is pretty haphazard at low revs.

 

[wjp]

Thanks for the help guys. I'll have a look this weekend.
Just a question though, when I look at the carb from the outside, on the left is the choke pull, then next to that there is a small screw which is nearly flush to the carb (whats that?) and then after that (going right) is a screw with a bolt holding the position against the carb. This is the screw that I have adjusted which makes it idle/not idle - I presume this is the airscrew? (maybe I shoudl get a digital camera!). I can't see an idle screw (with spring) anywhere. Has anyone got any photo's on the web of a YZ carb, as I think its where its from?

Thanks again.:)

 

[helio]

Maybe the following link will help you to identify your carb and their parts.

http://www.carbparts.com/

 

[JTT]

As I remember the screw with the nut is the idle screw, the smaller one is the air screw.

 

[David Trustrum]

Yeah sorry spring isn’t always visible, actually both have springs to stop them vibrating out. The idle adjuster can often be turned by hand. Either way if it is having a marked effect on the idle speed it is the idle speed adjuster. Some Mikuni flatsides don’t even have an air mixture adjuster.

 

[whyz]

Yup..

The idle screw is the one with the nut on it.in the middle of the carb.. the AS is on the Air boot side of the carb.(the one that is like 1/8 Small)..
So i got a question.. If the idle screw is the one that opens the air passage to let more air in to pull fuel in...It would pull it in faster giving you a faster idle? Right? :think So would that mean you could go lean on the PJ and would your idle go dow If you did? What im trying to get at is my PJ stock is 25..
AS=1 1/2 out. Now that its cold (kinda) 40 deg. i went to a 27.5 and 1 turn out..when i put the 25 back i have to go all the way in..
Would this mean that i might need an even richer PJ? Im back at 27.5 again to 1 turn out.. I was just trying to figure out how to get the AS to be set at 1 1/2 turns out.. have bad response with the 25 at 1/2 turn out but good with the 27.5 at 1 turn out.. but when i change it to a 30 it still at one turn out, with good response too but i can feel its alittle rich.
i just want to see if i can get good response with the AS at 1 1/2 turns out but only seem to get one out or 3/4..What gives.?:whiner: http://www.all-offroad.com/DirtBikes/Beginners/BGNov98.html
Thanks. Whoops i meant Air pulling fuel thru the PJ From the idle screw:think is that right?.. Great,,,,,,, Now I confused myself..

 

[JTT]

Ok, now I'm confused :silly: If it seems a little rich with the 30 and 1 turn out, why not go 1.5 - 2 turns and try to lean it a little? Remember there is going to be overlap in the effect of the screw and PJ. Don't get caught up in 1.5 turns, it can work anywhere within it's effective range (maybe 1-4 turns, dependant on carb). You will also find it beneficial to adjust the AS each time you ride, as it can be quite sensitive to atmospheric conditions, in some cases, and can make a significant difference in performance right off idle.

 

[whyz]

.. sorry.maybe im trying to think too much... :mad: now im all backwards.
I always adjust my AS anytime i ride..finding good response off idle..
Just wanted to know why the 2 diff. size PJ's were at the same amount of turns out to get good response. But the 30 seems alittle rich.. but same amount of turns out with good response off idle. it smokes but the 27.5 doesn't. if i turn any more than 1 turn out on any of these sizes it bogs when i wick it... my head hurts .sorry to make your's hurt too...
Does the idle screw have anything to with the lower circuit jetting?
im going to test what im trying to think of this week although i already did.
But ill play with it alittle more..I know how to jet my bike,i've learned it from here and there... it took me 3 months to finally get it down(testing)etc.
But now there's these off the wall Questions.. I feel so Blank.:confused:
Thanks....