Question about 2003 Yamaha YZ 125

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Pilot screw setting.

Ive fitted a new pilot screw (or air screw) on the carb of a yz85 2005 what is the correct setting for it starting from being screwed right in as far as it will go.i do understand all bikes are set up differantly and i can play with it once its running but i would like to no what is the correct starting point.

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Stock it would be around 2 turns out.

These bikes shipped with only one jet needle (unlike other Yamaha's) the bike's factory jetting is 45 pilot, NBKF needle on the 2nd clip from the top, and 138 main. This bike tends to run a little rich off the bottom, so I'd recommend running a 42 pilot instead. When it's really hot out (over 90) you can run the 135 main jet.

Screwwing with carbs is fact of life with these bikes - you will have to do some tweaking no matter what. pilot screw setting. - smile.gif

Posted on May 13, 2010

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It sound like the choke is stuck on or the pilot air screw is crudded up. Before removing pilot air screw make sure you know how many turns out it has to be adjusted to. Remove and clean the screw make sure the small hole this screw works with in the carb is not clogged. A thin brush fibre can be used to check this (do not use any thing metal). If necessary use a carb cleaner to remove any debris. Replace the pilot air screw very gently screw/turn into the carb until it becomes firm do not tighten any further. You now need to turn it back the number of turns the manufacturer states in the service manual.

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The screw I think you are adjusting is the idle mixture screw, and will only make a differnce at idle
You set at the smoothest idle
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If power in 1 and 2 is the problem, then there is something else, make sure the carb is clean, the exhaust is not blocked , the air filter is clean and relatively new,valve clearances? are ok, new spark plug , new oil, and then start looking at the jetting.
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By your description, it sounds like the pilot jet is plugged in the carb. Remove carb and clean thoroghly with carb cleaner and air, making sure that all jet passages are clear. Make sure that washer and "o" ring are present on fuel mixture screw, if so equipped. Make sure float level is correct.

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My name is justin i am 19 i have a 1991 yamaha fzr 600 and it kepps popping through first the first part of second my dad use to own a bike shop he said it was my piolit screws so he adjusted them it runs...


There isn't really a "correct" setting for the pilot screws. They're all set differently from the factory, based on the individual carb settings. You'll basically need to start at a baseline of 1.5-2 turns from seated (lightly seated) and work them in/out from there.

The first thing you should do before you go bothering to mess with settings, though, is clean your carbs thoroughly. Blow carb cleaner and compressed air through any of the passages in the carb body you can find, except the ones that lead up to the diaphragms, if you have CV carbs. You only need about 30 PSI if you can regulate your line pressure. Even a can of compressed air from Kmart will do, the stuff they use to blow out keyboards and such.

If you're really into time consuming stuff, you can buy a couple cans of compressed butane lighter fluid, and blow that through the pilot holes and such... you'll need a straw that fits on it, though. You'll be amazed what a good carb cleaning can do for a bike, as well as carb synchronizing. You can find specific directions for your fuzzer's carbs on just about any bike forum.

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Jun 22, 2009 | 2003 Yamaha YZ 125

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