Question about Yamaha YZ 250 F Motorcycles

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Proper air fuel mixture screw setting

2004 yz250f. have put a new tusk fuel screw in carb. set it to 2 turns out. But when i screw in in the revs go up and when i screw it out it starts to stumble. From my experience, this seems to be reverse to what i am use to ???

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  • Expert
  • 271 Answers

Yes, because it's not actually a "fuel screw", it's an air mixture.

Posted on Apr 16, 2014

  • 2 more comments 
  • Blair Gardner
    Blair Gardner Apr 19, 2014

    But it is in the fuel side of the carb, bot on the air side of the carb !

  • mj peterson Apr 24, 2014

    Technically, the air side. The pointed end of the screw moves into, or out of the air and atomized fuel path.

  • mj peterson Apr 24, 2014

    The adjustment was provided to accommodate elevation, Denver Colorado vs say, Tampa, Fl or any sea level area. Chances of harming your engine with these grossly out of wack are pretty small. You may also notice when out of adjustment the engine doesn't rev down crisply, it may slowly rev down or "hunt". Beginning in the 70s emission standards took away owner-adjustable jetting or mixture screws of any real impact

  • Blair Gardner
    Blair Gardner Apr 25, 2014

    good info thankyou.! Cheers

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Posted on Jan 02, 2017

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SOURCE: looking for the air fuel mixture screws on carb any help?

[IMG]http://i199.photobucket.com/albums/aa59/88gixxer/100_4177.jpg[/IMG]

Posted on Apr 09, 2009

  • 3 Answers

SOURCE: Fuel Air mixture screw

2 and a half make sure the bike's running when u do it the revs should sit between 1 and 3/ 2 2half

Posted on Jun 05, 2009

  • 3567 Answers

SOURCE: settings needed for mixture screws

Turn both screws inward and seat them GENTLY. Now turn both screws one and one half turns outward. This is the factory setting.

Please rate this solution as a "FixYa" Thanks!

Posted on Mar 19, 2009

emissionwiz
  • 74896 Answers

SOURCE: 1977 750gs carb sync

carb sync is done using only the carb hard stop adjustment u don't touch the air fuel mixture screw, had this exact same bike had the serive manual am dead sure on this

Posted on Aug 04, 2009

  • 302 Answers

SOURCE: piaggio nrg mc3 air carbrutor idle screw and air mixture settings

A service manual is a valuable tool with an aging bike. I suggest the dealer/mfr. or Clymer books. In the meantime, go to the library reference section...646 stacks should have what you need.

Posted on Oct 13, 2009

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1 Answer

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Hi, Anonymous and the usual suspects are:
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When i start the saw up it starts up but shuts off when you hit the gas and also when it starts up it just shuts off. I don't know how to adjust it to make it run so i am asking how to adjust it. I have...


The carb screws are fuel screws, not air screws, gently turn them both in ( clockwise ) onto there seats, now back off the L screw 1 1/2 turns, back the H screw off 1 turn, you will have to fine tune from there, start the saw, increase the idle screw so it will idle if needed, start by screwing the L screw in, the revs will start to increase due to the weakening mixture, it will eventually start to die as it is too weak, so at this point start unscrewing the screw 1/4 turn, rev the saw, it should pick up smoothly, if not increase the L screw another bit turn until it revs smoothly, now set the idle screw so it runs 3000 rpm approx, the H screw is the govenor, the more you screw it in the higher the revs, the max rpm should be set with a taco to 12500rpm, do not exceed this or it may seize, before any adjustment, replace the filter in the fuel tank, use fresh fuel, and clean the air filter.
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My Yamaha yz250F 07 starts first kick but back


I see: you changed the plug because it was backfiring.

Does it back fire when you let OFF the throttle after revving it, or does it back fire while being revved?

If it does it when you let off then Ollie's suggeston might do it. If that doesn't do it then check for dirt in your pilot jet.

If it back fires when revved up high could be dirt in your main jet.

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1 Answer

YZ250F is back firing when let off the throttle. Would hot start sticking cause this problem?


no buddy your mixture is too rich which means to much fuel is going in and not enough being burnt so the access fuel goes in the exhaust and then gets burnt in the exhaust which is a explosion so you get a back fire to cure this problem you need to screw the mixture screw in which is located on the carb a picture below will demonstrate turn this screw 1/4 of a turns in this will decrease the amount of fuel going in and stop backfiring good luck budbe6e0ee.jpg

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1 Answer

2006 1100 v star


Drain the carburetors. There should be a screw on the lower side of each carb float bowl. Remove the screw then replace it after the fuel drains. Remove the water trap bowl at the bottom of the petcock, (gas valve). Is there any water or trash in the bowl? Drain a cup of gas from the tank. Is there any water or trash in the cup? Dump it, clean it and re-mount it, (not all bikes have a water trap bowl). Turn the gas back on and wait a minute for the carbs to fill with gas. Install new stock NGK spark plugs and try to start the engine. If the bike doesn't start and run properly then shut off the gas and remove the carburetors from the engine.

FOR EACH CARB > Remove the float bowl and clean the entire
carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the idle screw and the air screw on the outside throat of the carb and spray into the screw holes as well.
< < READ CLOSELY > >
Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward. Put the rest of the
carb back together, clean the air filter and install the carb. Install an in-line fuel filter. Let the float bowl fill then start the engine. This process should get you back on the road.
Get back to me if the problem is still there.

Please rate this solution. Thanks!

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1 Answer

Wondering what the carb settings are for a 1983 yz250 my plug is fouling, i just put in a new one and it still fouled, its wet when i take it out, too much gas maybe? the bike smokes alot when i start it,...


The header says it is a 2004 YZ250F. That's a four stroke and gets no oil in the gas. Your 83 model is a two stroke. As far as the oil and gas mix, 32/1 is the proper mix. That's 4 ounces of two stroke oil per gallon of gas.
DO NOT USE STANDARD MOTOR OIL IN THE GAS.

Remove the water trap bowl at the bottom of the petcock, (gas valve). Any water or trash in the bowl? Drain a cup of gas from the tank. Any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).

Drain the carburetor. There should be a screw on the lower side of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install a new stock NGK spark plug and try to start the engine. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the two screws on the outside throat of the carb and spray into the screw holes as well.
< < READ CLOSELY > >
Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Be sure the bolts are tight. Let the float bowl fill then start the engine. Set the idle speed with the idle screw. This process should get you back on the road.


Please rate this solution. Thanks macnevind!

Apr 04, 2009 | 2004 Yamaha YZ 250 F

1 Answer

I have a keeway 125 bike new idle prob


Pull the carb off the bike and clean it inside and out. Be sure main jet is clear. Remove the two screws on the outside throat of the carb and spray into the screw holes as well. Be sure to put these two screws back in the same hole they came out of. IMPORTANT > > > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward.

Put the rest of the carb back together and install the carb. Turn the gas on to let the float bowl fill then start the engine. Chances are this will fix the problem. I suggest that you install an in-line fuel filter to prevent this happening again.

Last item> You should have just a little bit of slack in the throttle cable where it goes into the top of the carb. Not more than 1/16". Let me know how things turn out.

Please rate this solution as " FixYa " if all goes well. Thanks

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